Posts posted by DanielC
sorry i am new here, in fact a rookie in astronomy but anyway i tried to understand the 3d time but i couldnt understand how can time have 3 dimensions if it is a dimension itself in the 4d universe ?
Time does not have 3 dimensions. It never does.another thing how can we explain time is an event that is already here in space and we discover through living from past to present to future or is it defined by the speed of light and the distance it is traveling or in other words if we are in a place in the cosmos where there is no light (black holes) does time exist ?
If there is no light, time continues to exist. I don't think I understood your first question.0
then if there is dark energie there is wormholes right?
No. Wormholes are unrelated to "Dark Energy". Dark Energy is just a weird name that astronomers give to something they don't fully understand: Why is the universe expansion accelerating?0
i saw a documentary lately that fascinated me it said that time travel to the future is something very real and achievable proven by einstein theorie of general relativity
If you get on a rocket, travel close to the speed of light, turn around and come back to earth close to the speed of light, you will have aged less than people on earth.then i researched and found that if we go to the quantum level we would find that an idea that occures to us many times in life may be real . there are different dimensions parallele ones . in other words i exist in different dimensions and in each i am different due to what i changed for example : in one i am a business graduate in another i didnt go to college.
This is the many-worlds interpretation of quantum theory. It is not a scientific fact, and it is not something you can prove. It is just an idea that some people have. Btw, it is best to not use the word "dimensions" to mean "parallel universe". Dimensions are just a mathematical concept and it is best not to mix it up with sci-fi ideas, otherwise you can get more confused.0
You have spent the last week or two basically arguing that you can overthrow the last 80 years of astrophysics progress without even bothering to grab a physics book and learn how anything works. Instead of calling you an idiot, I have taken a lot of time out of my astrophysics work to explain to you a lot of elementary physics, like pressure, orbits, electromagnetic force, nuclear burning, and so on. These are all things that I understand very deeply. When I pointed out one area where I am not entirely knowledgeable, you proceeded to insult me, saying that I just take equations on faith, while ignoring the dozen times where you just blindly took a vague physical notion on faith and tried to apply it in an inapplicable context. Btw, I do know the derivation of electron degeneracy pressure, but I can still say that I don't know the subject as deeply as the others. Nobody is an expert on everything.
I am very busy doing astrophysics. I've taken some time to come to this forum to help people who want to ask an astrophysicist how something works. I think that the time I've spent with you was wasted.Do you think I am talking about gravitational lensing occurring somewhere outside the Milky Way galaxy?
No, I never had that impression. You were proposing that the Milky Way somehow caused a really weird type of gravitational lensing that somehow (1) made things look further way, (2) made things look like they are moving, and above all, (4) did all these things in a finely-tuned way that was direction dependent, causing one galaxy appear to move much faster than one standing right next to it in our field of view, and do this billions and billions of times, in a way that is precisely tuned so as to make us believe that the universe expansion follows a pattern of deceleration, followed by constant expansion, followed by deceleration, in a way that just happens to fit the effects of a gravitational constant. Oh, and lets not forget that this magical gravitational field must also be intelligent enough to make the galaxies that are less evolved, an show less metallicity, and greater star formation, also appear to correspond to the galaxies that are further away and receeding faster.
Lastly, let's not forget that seeing galaxies move apart is just ONE piece of evidence that the universe is expanding. There is also the fact that GR (which is well tested) predicts that the universe should be expanding or contracting, and that the cosmic microwave background provides a key piece of evidence for the Big Bang theory. Thus, by proposing that the universe is not actually expanding, you are implying that GR is wrong. Trying to prove that you have a better theory than GR would be a bit of a challenge.Which math?
You don't think astronomers use math?
Let me show you a very simplified data set, and I'd like you to try to explain it using your magical-gravity theory. You don't have to give me the answer. Just think about it and try to explain it mathematically with pencil and paper:
You observe four galaxies, all next to each other. In each one you see a Type Ia supernova with identical light curves. Those supernovae have luminosities of 1.0, 0.25, 0.11 and 0.06, in some appropriate luminosity scale. You use the Doppler shift tof these galaxies to get their speed relative to you. They are 2 km/s, 3.5 km/s, 5 km/s and 6.5 km/s respectively.
I'll show you how you could explain this in simple terms:
The Type Ia supernovae have identical light curves, so we know that their inherent brightness is the same. So we can use the inverse luminosity square law to find the relative distance of these galaxies:
sqrt(1/1.00) = 1.00 D
sqrt(1/0.25) = 2.00 D
sqrt(1/0.11) = 3.01 D
sqrt(1/0.06) = 4.08 D
Where D is some unit of distance. So that's how we estimate their distances. Now we look at the radial speeds we got from the redshifts: 2 km/s, 3.5 km/s, 5 km/s and 6.5 km/s. We notice that galaxies farther away seem to move faster. We make this more precise by estimating the relationship between distance and speed:
v = 1.5 (km/s)/D
This is the equivalent of the Hubble constant in the real universe. Now we combine this with General Relativity, and specifically the Friedmann equations[/b] to determine the expansion of the universe.
This simplified example is the most basic bit of cosmology that your theory needs to explain. I have not introduced complications like dark energy. You need to think about how you would explain these observations quantitatively in a universe that works the way you propose.
I did much more than that. You just happen to ignore stuff you don't want to hear. I said that there were various effects that were far more important than friction from the interstellar medium, and I spent an inordinate amount of time trying to explain this very elementary concept because you don't want to understand how anything works.
See? You don't listen. That is not what they said. I said that the sun losing mass will not cause them to drift away. But there are other things in the universe that might. For example, planet-planet interactions can cause planets to be ejected, and so can close encounters with other stars. I think that your problem is that you want a simplistic explanation that considers only one factor and ignores everything else. The universe rarely works that way. The sun losing mass will cause planet orbits to expand. Chaotic gravitational interactions can cause planets to come closer, or be ejected.
Yes. You can look at the luminosity of a galaxy to figure out how many stars it has, you can look at the colour of stars, which also gives you an indication of how much mass they have. We also have many tests that confirm General relativity: Pulsar timings, gravitational lensing near the sun, and GPS satellites (which wouldn't work if general relativity was wrong). GR has been confirmed to work to extremely accurate levels of precision, and you can derive Newton's inverse square law as a low-gravity approximation to GR.
Don't you realize that all your arguments are based on ignorance? I'm tired of this. I've spent way too much time being polite to you while you try to convince me that you can overthrow astrophysics without knowing the difference between an object in orbit and a light gas floating by waving your hands in the air and saying that it's all just energy that ultimately came from the Big Bang.0
AFAIK, the Heat Death is currently favored by our observations, althought a Big Rip is not entirely ruled out.
From my understanding the cosmological constant is used for when the expansion is accelerating at a constant rate leading to not bound systems to drift apart and eventually reach and pass their cosmic horizons, whereas phantom energy causes the expansion to accelerate at an accelerating rate, leading to bound systems being ripped apart.
I'm sure you are right. The end-state of the universe is not my area of astrophysics. I'm more familiar with things like stars, white dwarfs and neutron stars. I want to go into exoplanet research. I know GR, but the things you normally learn when you study GR are mainly the Big Bang and lack holes. I don't think the terms "Heat Death" or "Big Rip" ever came up in class.
So let's see, in that case the end of the universe will be a bunch of massive objects flying around in big empty space (planets, white dwarfs, neutron stars, BHs). Eventually the BHs evaporate, but other than that I can't think of anything interesting happening in the universe as it slides toward increasing entropy.0
I thought the purpose of longer exposures was to capture more light from very dim objects... I didn't know this had an effect on the actual resolution of the image.
I am pretty sure that this is the case. I cannot imagine any way that a longer exposure improves resolution, it just gathers more light (allowing you to see fainter objects). To improve the resolution you need a larger aperture (assuming the telescope is in space, or you have adaptive optics).I was under the impression that the further you go to that side of the visible spectrum, the worse the resolution got (with the same size instrument)... I don't know why I have that idea.
Technically, this is correct, but instead of a rocket telescope you can just make your telescope wider and get the same result. Basically, the resolution limit of a telescope is equal to wavelength divided by telescope width. In principle, I guess that a rocket telescope travelling close to the speed of light would get an advantage with the wavelength, but it is much easier to spend your money making the telescope larger instead.0
Even if we can't see more of the universe in this fashion, it still seems to me that we would be able to get a better (clearer) picture, since we have reduced the distance 7 fold?
I don't think it would. The picture quality depends on the size of your telescope. The wave nature of light causes a distortion pattern called an Airy disk, which is the maximum resolution a telescope can have, and it depends on the size of the telescope. Moving the telescope very fast would not change this. It would collect photons faster, but by the time the rocket telescope gets back to earth, all those photons would have arrived here anyway, so we would have gotten the same picture by just leaving the telescope camera on the whole time.
Why such a hesitant answer? It seems to me that, even if our observable universe did not get bigger, the farthest stuff we can see would become much less red-shifted, and therefore easier for us to see.?
Why does red-shifting make things harder to see? It just moves the light to a different part of the spectrum...0
I'm a rookie on these topics so please excuse me if I am out of place here, but as Spyman pointed out in another thread:
The expansion of the universe is accelerating. Over time it becomes significant at smaller distances.
If the magnifying glass was changing density, it could make spatial relations outside the lens appear to be expanding or contracting.
No. And astronomers are not so stupid as to be fooled by something as lame as gravitational lensing. Second, notice that you keep invoking more and more magical forms of "gravitational lensing" without actually knowing how it works, in an attempt to force your hypothesis. Gravitational lensing will not give the appearance of an expanding universe unless the astronomer can't do basic math. For one, gravitational lensing will not cause some galaxies to appear to move at different speeds from others, and it certainly will not cause the complex distance/speed relationship that indicates a universe that initially slowed down and later began to accelerate.
If a galaxy was contracting, gravitation levels could be rising, which could be steadily increasing the optical-density differential between the interior of the galaxy and the more empty space between galaxies.
I'm sorry, but you don't know what you are talking about. You just keep cobbling words together without thinking and I am getting frustrated that you can't be bothered to understand how gravitational lensing actually works, but you continue to insists that for 30 years astronomers have been unable to do math.
The speed of light is the maximum speed possible in any medium. So C changes in material media, such as water, but also due to gravitation, which is the cause of gravitational redshift, I beleive.
You are wrong, of course. You have not the faintest clue how gravitational redshift works. No, gravity does not change the speed of light, (which is a lower-case "c" btw), it makes photons lose energy causing their frequency to shift toward the red (hence the term "red-shift").
Idk, I'm still not convinced that lens-effects couldn't cause some objects to appear to recede faster or slower than others. Remember, I'm not talking about a stable lens but one that is changing shape and density at a variable rate depending on the changing gravitational field relations of the galaxy's constituents.
Try for a second to understand the absurdity of what you are suggesting. You are proposing that gravitational lensing does something that it does not do (make light go slower) while constantly changing, in an incredibly fine-tune way so as to make a further way galaxy appear to be receding 10 times faster than another nearby galaxy sitting right next to it on the sky. With billions and billions of galaxies observed, you propose some weird magical gravitational lens with billions and billions of lumps, just exactly located to match the locations of these galaxies, to give the impression of a universe that in earlier times was slowing down, and in more recent times began speeding up, in a way that just happens to fit into a form compatible with Einsteins theory of relativity, which has been tested to an incredible level of precision. In other words, you are proposing that the universe has an incredibly complex and weird set of physical laws, which are finely tuned with the very specific effect of making humans on earth think that the universe actually has a completely different, very precisely measured, set of physical laws.
With your line of argument you would be better off saying that the universe appeared last week and that it looks the way it does because God made it look that way.
Well, what happens to them then? They continue to be negatively charged while the protons continue to be positively charged, no?
Electrons and protons don't lose their charge. That doesn't mean that electrons have anything to do with nuclear fusion. Again, you have no idea what you are talking about, and in your ignorance you keep repeating things that make no sense because you cannot accept it when someone who actually studied the subject tells you that electrons are not relevant for the process of nuclear fusion... Did I mention that I'm frustrated?
So you're another person who accepts the calculations without having an explanatory mechanism for how the process actually works outside of the math?
Nobody nows everything, and between the two of us, I have gone a lot more deeply into the physical processes than you have, since my field is astrophysics. I bet that I am more familiar with the experimental evidence for particle physics than you are. So don't try to lecture me about understanding physical mechanisms. In this discussion you have shown yourself unwilling to grab a physics textbook to learn anything about how physics works, like how planets stay in orbit, the density of the interstellar medium, the process of nuclear reactions, or the behaviour of gravitational lensing, while I have spent a lot more time than you deserve explaining how all these physical processes work and doing various calculations when appropriate, while you continue to close your mind and insist that whatever half-baked idea just crossed your mind must be correct. It sure must be very easy for you to not feel the burden to prove any of your hypotheses.
I suppose the Earth does have a great deal of momentum considering its mass. I suppose I'll have to concede that your idea that the sun will lose mass due to fusion will cause the planets to expand in their orbits and eventually drift off into interstellar space.
I did not say that when the sun loses mass it will cause planets to drift into interstellar space. Furthermore, fusion on itself does not cause mass loss. The mass loss is caused by stronger stellar winds during the red giant phase, and the result is that the orbits expand, but not that planets drift off into space. It looks like you haven't actually bothered to read much of the explanations I gave. It looks like I've wasted my time trying to explain science to you. I should spend my time with people who actually came to this forum to learn about science.
But then, how else do you measure the mass of a body except by its gravitational effects?
You don't measure the mass of almost anything with gravitational lensing. Gravitational lensing is far too weak for that. The way you measure mass depends on the object in question. For planets in the solar system, and for stars in binary systems, you can measure the size and period of some orbits (e.g. the moons of Jupiter allow you to measure Jupiter's mass). Similarly, the rotational speed of galaxies tells you how much mass they have and how it is distributed. You can also derive equations of state for a ball of gas, which allow you to establish a mass-luminosity relationship for stars. Combined with measurements of the mass of the sun, and stars in binary systems, we can effectively deduce the mass of other stars as well. Etc etc.0
How do you know this? Obviously there are competing interests and symbiotes. What makes you so sure humans have more competitors than symbiotes?
A simple plot of earth's biodiversity against time will show a steady drop ever since the earliest hunters began killing all the mega-fauna in almost every continent thousands of years ago, and continuing through the modern era through massive deforestation, pollution, over-fishing, and so on.
We need to take all of the predictions of water and goldilock's zone with a massive pinch of salt
No one has predicted water as far as I know. I read the paper and they found a good signal for a planet smack in the middle of the Goldilocks zone. We don't know what the planet is made off, except that its mass is consistent with a rocky planet. The Goldilocks zone is defined as the region around the star where it is possible for liquid water to exist. That is all that I've said. Nothing more, nothing less.0
If two balloons were next to each other and shrinking, an observer inside one of the balloons could conclude that they were moving away from each other.
No, he wouldn't, unless he was not a very smart observer. Incidentally, we do not measure the expansion of the universe by seeing stuff shrink. We use various techniques such as Type Ia supernovae, Cepheid variables and Doppler shift to measure distances and speed.
Second, galaxies are not shrinking, and gravitational lensing would not make it look like they are. The best analogy I can think of is: If you put a magnifying lens in front of an object, it might make the object look bigger and brighter, but it will not make the object look like it's moving.This, I would expect, would increase the apparent expansion because relative to the speed of light as measured within the galaxy, the speed of light outside it would be (lower? . . . this is where I get mixed up whether higher gravity slows or accelerates light).
It does neither. The speed of light is a universal constant. Light is not accelerated or decelerated by gravitational fields. Gravitational fields can bend light, but they do not change the speed of light.Still, you get my point: objects may be more distant than they appear and this effect may be steadily increasing causing the appearance of expansion.
This is wrong for a few reasons: (1) We do not (and cannot) use the angular size of galaxies to determine their distance or speed. (2) Even if we did, and even if the galaxy's gravitational field changed their apparent size the way you suggest (it doesn't), that would not make us get the speed wrong, unless this strange gravitational lensing that you propose was also changing in time. (3) And even if we did have this magical, time-changing, gravitational field you propose, it would not make objects further away look like they are moving faster than those nearby. (4) And even if we did have this super-magical gravitational lensing that somehow could discriminate distance to make further-away objects look like they are moving faster, that still would not fit observations because the expansion rate that we measure is not a simple acceleration curve. What we observe is that the very young universe was decelerating, as you would expect in a matter-dominated universe, while the older, more recent universe is accelerating away, and the shift between the two matches that of a universe that is initially matter dominated, and as it expands, the cosmological constant becomes more significant.
The protons and electrons may not be bound, but that doesn't mean their flows relative to each other and themselves are not influenced by their interactive tendencies. They are, after all attracted to each other by opposite charge. So the ability for protons to come into contact and be compressed beyond their repulsion would still be mitigated by the force required to displace electrons, which probably also has something to do with whether fusion results in helium or a heavier element. I.e. it probably takes more energy to get 3 or more protons next to each other and compressed to the point of fusion than it does for 2.
I'm sorry, but you have no idea what you are talking about. Electrons are not at all involved in the process of fusion, and they have no effect whatsoever on the ability of protons inside a stellar core to come close enough for the strong force to work.But how would this alter the overall compression of the particles?
I should mention that I am not an expert in quantum mechanics. The Heisenberg principle does not compress particles. It says that when you compress particles, their momentum becomes less certain. And through some calculations that I only more-or-less follow, you can show that this gives you a source of pressure that is independent of temperature.
And both its slowness and thinness may become fastness and thickness as it descends into the gravity well of a dying/deceased star, no?
I was thinking more that the heliopause was the edge of an energy-bubble resulting from solar wind but also radiation and heat. Lighter gases tend to rise in a gravity-well, no, especially when heated?
No. Lighter gases do not rise in a gravity well when heated. This is the sort of thinking that is based on your experience here on earth, sounds intuitive, but has no reality in the near vacuum of space. On earth, and on the sun, lighter gases float. But this cannot be extended to orbiting objects in a solar system.
But to make you feel better, lets suppose that if you turned off the solar wind, the interstellar gas would condense around the sun the way you suggest. The pressure from this gas would not be greater than the pressure that earth already feels from the solar wind, right? (otherwise, the solar wind would not be pushing it). So let's take the entire pressure from the solar wind, and instead of being random, lets assume that you put all that energy into slowing down the earth, with perfect 100% efficiency. How long would it take for this pressure to make the earth fall onto the sun? I did a calculation, and the answer was 222,000 times the present age of the universe.
Do you now believe me that the friction from the interstellar medium is negligible compared to other factors?
I know this is based on Newton's equation which considers only mass and distance. However, don't you think that matter whose mass is spread out less densely has the tendency to cancel out a certain amount of its gravitation.
This is not true. This is not simply a supposition that we just make for simplicity, it is something that you can prove by integrating the gravitational force of every infinitesimal mass from a spherically symmetric volume.
Look, if there is one thing astronomers should understand, it's gravity, because that is the force that dominates everything in the universe. Astronomers don't just hypothesize about how gravity might work. We have very precise theories of gravity that have been experimentally verified to incredible levels of accuracy.The center of the Earth, for example, is weightless because the gravity from the outer layers of the sphere cancels itself out completely in the center.
You can derive this fact from what I said in my previous post. I told you that if you are inside the earth, the gravitational attraction corresponds to the mass in the sphere below you. So as you go down, the gravity you feel drops.
Nevertheless, the gravity from the North pole is less by the time it reaches the South pole than it would be if the two poles were compressed into the same point, no? So I would actually think that gravitational fields extend farther from denser bodies than more voluminous ones with the same mass.
Gravity does not extend further from denser bodies. If it did, astronomical observations would have revealed that long ago. We have a wide range of both very light and very dense bodies with which to test our theories of gravity, and all tests match our existing theories.But are there equations and experiments for predicting the effect on light if we were located inside a gravitational lens?
Einstein's equations are perfectly general. They work just fine for observers inside the galaxy. They can also tell you what an observer entering a black hole would see, or what an observer in an accelerating rocket would see, etc.0
So we seem to be in agreement, but why then are you quoting me instead of Almehdi, who is the one asking about "accelerating expansion speed versus mass gain of the universe" ?
I was agreeing with your post.1
Interesting. And what do they do after being ejected into "empty space?" Do they not coalesce into new galaxies eventually?
They don't. Remember that the universe is expanding. If the universe was static, we could conclude that sooner or later they would hit something. But as the universe expands, space just gets emptier and emptier. If you imagine a lone white dwarf that has been ejected from the Milky Way, in theory there is some galaxy "in front", some huge distance ahead. But that galaxy is moving away too, as the universe expands. So as time goes by, the Milky Way is further and further behind, and the galaxy in front is further and further away too, and the white dwarf just gets more and more isolated. It would just be a few white dwarfs that just happen to be flung in the direction of a nearby galaxy that is not receding away.
I think we're talking about opposite sides of the same coin, but maybe I misunderstand. The strong force is attractive, but it can only bond the two protons once they are sufficiently close, right?
To get this close, they have to get beyond their electron clouds/shells/whatever.
Incorrect. We are talking about protons getting close to each other. Electrons are not involved. The sun's core is a ball of ionized gas where basically the electrons and protons are not bound to each other. What we have to overcome is the repulsive force of two protons, because they both have a positive charge and they repel.
Fine, apology accepted. Either of us may have insights that the other one lacks, but if we make this into a pissing contest it will only detract from the productivity of the discussion, right?
Keep in mind that I am a graduate student in astrophysics. I try to explain things clearly and politely. I am in this forum in the hope that I can help people understand astrophysics better. I am not here in order to insult people, but if you say something that is wrong in this forum, I imagine that it is acceptable for me to say so. I try to say it politely, but I also try to give enough details that you understand why the universe works the way it does. I hope that you will not take my explanations as an insult. Would you really be happier if I simply said that you are wrong and didn't try to give more details?
A (core collapse) supernova explosion is a hugely energetic process where atoms nuclei can be banged together with enough force to make them fuse, even if that reaction consumes energy. In a (core-collapse) supernova, a lot of things happen that actually consume energy. For example, at the high energies of the explosion, photons have enough energy that they can actually break apart iron nuclei into smaller pieces, essentially running fusion backward, even though this reaction consumes a lot of energy.
The energy source of a core collapse supernova is gravitational potential, which is about 100 times greater than the nuclear energy, so there is plenty of energy to go around to force matter to things that actually consume nuclear energy.
As one point of clarity: A core-collapse supernova is one type of supernova. Basically, a "type Ia" supernova is something else, and every other type is ultimately a core-collapse.
Then I don't get how you're saying that Heisenberg uncertainty relates to particle momentum. Do the particles themselves have volume or are they points? If they are pure zero-dimensional points, can they be compressed limitlessly?
Quantum mechanics models particles as points or waves, not as objects with a definite volume.
Heisenberg's uncertainty principle says that a particle's position and its momentum are not definitive quantities that can be known exactly. Let "dx" be the uncertainty in the position of a particle. Let "dp" be the uncertainty in a particle's momentum. Heisenberg's uncertainty principle says that "dx * dp > h" where h is Planck's constant, which is a very small number. For most things in life this relation doesn't say anything interesting. In a white dwarf, electrons are confined within a very small space, of a size comparable to "h", and as they are more compressed, their momentum must be more uncertain, which means that it spans a greater range of values.
Nice quantification of the issues involved. So the stuff beyond the heliopause is moving very slowly.
The main point is not that it moves slowly, but that it is very thin. The interstellar medium is practically empty. The scale of the interstellar medium having any effect on planets is many magnitudes longer than other effects such as planet-planet interactions or a close encounter with another star causing planets to move out.What do you expect at such a high altitude in a gravity-well? Once that stuff starts to descend into the gravity-well, though, don't you think it will accelerate? By the time it gets to the planets it may have quite some momentum, no?
Here is a persistent problem with your thinking: You keep imagining stuff just has a natural tendency to fall toward the sun and that stuff is held "up" by some form of pressure. This is not the case. The galaxy is full of forces, with multiple stellar winds, as well as everything orbiting the galaxy in their own orbits. The heliopause is the point where the solar wind becomes comparable with these other forces. It is wrong to think of the heliopause as some cloud of gas that is stuck with the sun and is just waiting to come down when the sun turns off. The heliopause is where the sun's influence becomes no greater than the other normal effects that you get from other stars, or from each particle having its own orbit around the galaxy.
A distant observer, maybe, but what about the dynamics of the system internally?
As a way of example: You are sitting on earth. You are not very far from earth. The gravity that you feel is basically indistinguishable from the gravity that you would feel if all of earth's mass was concentrated at a single point at the centre of the earth. Now imagine that you are 3,000 km down into the earth. Now the gravity that you feel is different. Basically you only feel the gravity of the mass that is below you, but as long as you have spherical symmetry, the gravity that you feel is indistinguishable from what you'd feel if all the mass below you was concentrated at a single point at the centre of the sphere. In a similar way, it is not the same thing being in the middle of a globular cluster with 1 million stars, versus being next to a 1 million solar mass black hole. A black hole would give you things like an event horizon. But notice that most of what you have been talking about in your posts have been references to distant observers. For example, look at the following:
Light will change directions much more traveling through a cloud of dents in spacetime than through a single large gravity-well, no?
This is a reference to what distant observers will see. You are an observing some distant object, and its light could pass through a gravity well formed by either a single huge black hole, or by large number of small stars. To the best of my knowledge, the bending of light would be the same in either case.
I don't know. Personally, I think that gravitational lensing is treated as too isolated a phenomenon. After all, if you look at the variety of optical effects that exist terrestrially, why would you expect in less variety extra-terrestrially? Imo, we're just not able to explore the universe as thoroughly as terrestrial space, so we're somewhat alienated from being able to recognize all the optical variations.
We can see a heck of a lot of universe. Gravitational lensing has been observed many times, always in accordance to Einstein's field equations. Gravitational lensing is a fairly well understood phenomenon. It is worth highlighting that our understanding of gravitational lensing comes from Einstein's field equations, which have been tested very throughly. Some people have this image of physicists looking up at the sky and assuming that whatever they haven't seen yet must not exist. This isn't how we work. We form a model of the universe, and we test it throughly. It is worth noting that gravitational lensing was predicted by Einstein's field equations, and once physicists saw the prediction, they went to look for it (and they saw it).1
There are a lot of calculations and competing models but to my understandig there has not been any observations of the slightest mass gain of the whole Universe.
Cosmology is not my field, but I certainly haven't hear anything about mass gain in the universe, other than the Steady State theory, which suggested that there was no Big Bang, but instead as the universe expands new matter is constantly create to fill up the empty space, so the universe always looks more or less the same. But that theory was debunked a very long time ago with the discovery of the Cosmic Microwave Background Radiation, which is predicted by the Big Bang, and cannot be explained by the steady state.0
We are only able to see so much of the universe. Can we alter this?...
Say we built a rocket telescope and fired it directly toward a specific area of space... say the hubble deep field area. We get this rocket going about .99c and then let it coast for a day or a week... however long it takes to get a good exposure. Then we turn the rocket around and have a look at the photo... what would we see?
Would we see farther than the observable universe we experience on Earth? (since distance has contracted in the direction of travel)
No, we wouldn't see any further. Any picture that the rocket telescope could bring us would be a picture that we ourselves produced years before. Because the rocket travels slower than the speed of light, the light that it captures is travelling faster than the rocket, and that light would get to earth sooner than the rocket can. Let's make up some numbers to make the point clear:
Imagine that 13 billion years ago there is a supernova explosion in some distant galaxy. The rocket is 1000 light years closer to that galaxy than the earth is, so it sees the explosion 1000 years before we do. Then that rocket travels at 0.99c toward earth, and so it takes 1010 years to get to earth. By the time the rocket gets back, our astronomers would have seen that explosion 10 years prior.Would red-shifting be (to some degree) reversed by our velocity toward the light we are collecting?
In principle, I guess the image would be less red-shifted.0
hi group!! in responce to Gliese 581g being Earth-like,as many of you pointed out,it is not Earth-like at all,most certainly a toxic hell where no life can exist.
At best, this is an argument about scemantics. As an astronomer, I consider a planet "Earth-like" if it is a rocky planet with a surface gravity similar to the Earth and it is located in the region where liquid water can exist. Incidentally, you have no basis on which to claim that it is "most certainly a toxic hell". How do you know that?
the so called ''goldilocks zones'' probably dont exist either,
The "Goldilocks zone" certainly exists. The term comes from the children's story "Goldilocks and the Three Bears" where Goldilocks eats the little bear's soup because it was neither too warm nor too col. Every star has a region around it where liquid water can exist. This is what is referred to as the Goldilocks zone.Earth acts as a huge organism,where all life is interconnected,and dependent on all the others,for instance,if you wiped out all the plankton,the entire food chain would fall apart,rendering the Earth almost devoid of ambulatory creatures.
Not entirely true. If you wiped out all humans, the rest of the earth would be better off.it is plain that Gliese 581g doesnt have this ability.
Why not? Nobody can make that assertion.0
Eventually, I could see how if everything has already fallen into black holes, the black holes themselves will slowly radiate into masslessness, but they have to capture all the other matter-energy first, no?
No. And in fact, they won't.
This is the key point of our discussion, so it is worth making it clear. I know that you want to hear that at some point everything will end up inside black holes, but I'm pretty sure that that isn't true. This is how the long term future of the galaxy is likely to play out:
Long after all the stars have died, you have a galaxy full of white dwarfs, with a small number of neutron stars and fewer black holes. Once in a while two white dwarfs come close to each other and exchange momentum, with one being sent outward and the other inward, and some times being ejected. As time goes by, white dwarfs are steadily ejected out of the galaxy while at the same time the smaller, remaining galaxy becomes denser. As the galaxy becomes denser, these close encounters happen more frequently and the process accelerates. At the end of the process you find that the great majority of the white dwarfs in the galaxy have been ejected, while a small fraction have coalesced into the central galactic black hole. In this way, the vast majority of the white dwarfs never end up inside a black hole and they just travel alone through
Put it this way: if it was possible to pull the two protons of a helium atom apart and stabilize them as hydrogen atoms, the process would be endothermic, correct? In fact, wouldn't the amount of energy invested in separating them be equal to the amount that would be released by re-fusing them? Isn't this similar to investing energy in pumping water uphill and then releasing that (potential) energy by allowing the water to flow back down hill and drive a turbine?
You said that "the potential energy in their separation/repulsion is expended". This is not true. The energy from fusion doesn't come from the proton-proton repulsion, it comes from the strong nuclear force which is attractive. You can say that before fusion, hydrogen atoms have a form of potential energy, but you cannot say that their repulsion is expended, or that their repulsion is the source of the energy. Quite the opposite, the repulsion serves to decrease how much energy you can get out fusion.
I'm sure it is quite important for your self-esteem to establish an asymmetrical relationship between us in this discussion but my interest here is physics, not the social relations of the discussion.
This is not about my self-esteem. I prefer to clarify and give detailed explanations rather than say "you are wrong, trust me" because if I do that I am not doing my job as a scientist. Sorry if some of that came across badly.
And when lead is reached, does fusion continue only now endothermically? I assume this is how uranium and other unstable elements get formed. But you are clearly the expert.
Fusion stops at iron. AFAIK heavier elements are produced in supernova explosions.
Why isn't the average momentum the same thing as heat? Are you saying that due to very high compression, momentum becomes intermittent instead of consistent?
Heat is average kinetic energy per particle, and while it is not the same as momentum, it is correct that they go together. No, momentum does not become intermittent at high compressions. All I tried to say is that the source of pressure is grounded on quantum mechanics and the Heisenberg uncertainty principle rather than the usual ideal gas law. Among other things, it means that no matter how long you wait, the white dwarf will never compress further on its own (unlike a star, which can radiate heat and shrink).
Have you thought about what I said about the sun's radiation and the maintenance of the heliopause? It may be that stars create a frictionless bubble using their radiation which permits planets to form stable frictionless orbits while they are radiating sufficient energy to maintain the relative vacuum. In this sense, interstellar space may be much less vacuum-like and chaotic enough to result in very different gravity-space relations as within the heliospheres formed by stars.
Let's do a calculation: The heliopause is about 153 AU away from the sun. At that distance, the solar wind is about 153^2 = 23409 times weaker than it is here on earth. Actually, it's weaker than that because the particles slow down, but let's use 23400 as our estimate. That means that the force / momentum from the interstellar medium is more than 23 thousand times weaker than the force that the earth already receives from the solar wind. But you don't hear anything about earth spiraling outward due to the solar wind. Earth has been going around the sun for 1/3 the age of the age of the universe and over that scale the effect of the solar wind is not even measurable. That means that if you wait (1/3) x 23400 = 7,700 times the age of the current age of the universe, the effect of the interstellar medium will still be not measurable. There are other effects that will become significant long before you've waited 8,000 times the present age of the universe.
So you think there is no difference in the spacetime fabric topology of numerous small gravity-wells verses on very large unified gravity well?
You can prove that the gravitational force felt by a distant observer is the same, regardless of whether the gravity comes from numerous small gravity wells or one very large one.
Because gravity dilates/contracts spacetime. Theoretically, shouldn't each galaxy have a certain gravitational lensing effect due to its gravitational web? As such, isn't observing from inside a galaxy somewhat like observing the outside of a lens from inside of it?
Gravitational lensing is a real, but well understood phenomenon. We do not experience gravitational lensing just because we are inside a galaxy. The gravitational lensing we observe is from massive objects lying between us an whatever we are observing. Gravitational lensing will not give the appearance of expansing. It will make objects look deformed, and it can make some galaxies look brighter. But none of that has to do with how we measure the expansion of the universe, which is by taking the Doppler shift of many galaxies and comparing it with luminosity data from Type Ia supernovae.
I'm sorry DanielC, but I am going to have to call you on this one. The link you provided does not support your statement. The 'Big Freeze' is based on stars using up all their fuel, and proton decay. What you are describing is called the 'Big Rip' and is based on the possibility that the cosmological constant is not a constant at all, but is increasing over time.
I am used to being humbled, so I won't feel too bad if you prove me wrong on this.
I am not an expert on cosmology, so I might have used some terms wrong, and I might have some timescales wrong. But I'm fairly confident that you don't need a variable cosmological constant to have galaxies tear apart. The cosmological constant means that the expansion of the universe is accelerating. That tells me that the expansion will become significant at the galactic scale sooner or later. But perhaps I'm wrong...
To maintain the conservation of energy, relativistic mass needs to be absolute, independent of reference. That means that at some level of observation, space and time also need to be absolute and not relative.
This is not correct. In special relativity, the laws of conservation of mass, energy and momentum are simply replaced by a single law of conservation of the four-momentum tensor, whose magnitude is (E^2 - |pc|^2). This is a quantity that all observers will agree on, and it does not necessitate an absolute space or time. This is akin to conservation of momentum in classical physics. The momentum components in the x, y and z directions need not be conserved, but the total momentum is conserve.0
You just perfectly avoided getting my point, why?
Perhaps your point was poorly stated. You make several leaps of logic and you use unusual terminology.
The point was that the kinetic energy, i.e. momentum, of the objects/particles results in volume of the system. Pressure is basically a function of gravity.
Pressure depends on many things, and gravity is but one of them. For example, the solar system and the galaxy are not held up by pressure in any way, manner or form. This is an important point because you are trying to equate the behaviour of a star (which you understand poorly) with the behaviour of the solar system and the galaxy (which is incorrect).
When orbiting objects slow down, they fall into the gravity well. If they gain more velocity in a non-downward direction, they gain altitude.
The second statement is incorrect. Consider a thrust in the direction opposite to their motion for example.
Good description. Now consider that the solar system is de-frictioned by the heliotrope remaining at a far distance from the sun. If the sun would stop radiating energy and solar wind, would the heliotrope not collapse and result in much friction for the planets?
You overestimate the density of the interstellar medium. Furthermore, notice that none of this is related to the claims you have been trying to support:
1) Friction from the interstellar medium has nothing to do with the gas pressure that is responsible for how stars work.
2) Friction from the interstellar medium does not justify you making a connection with how stars work and how a galaxy is held up, and it certainly doesn't justify you using fuzzy terms like "expansionary energy" that have no clear meaning.
Why? Doesn't gravity cause pressure, pressure cause heat, and pressure and heat cause fusion?
Under some conditions. And if you don't stop to think about when that is true and why, you will reach strange conclusions like thinking that what holds stars up and what holds a galaxy up are somehow the same thing.
I know that. I was referring to light weight gasses coagulating into stars.
Note that it is difficult to know how much you know because you've made some strange connections between the pressure that holds a star in place
Because without any momentum being added to it, it is in line to. It's just a question of time until the friction it encounters decelerates it to a degenerative orbit.
Try to do a calculation comparing friction from the interstellar medium against Jupiter versus the expansion of the universe. Even without the expansion of the universe, can you even show that friction from the interstellar medium will cause Jupiter to spiral inward? After all, you could just as well imagine that the in-falling material would add kinetic energy to Jupiter and raise it to a higher orbit.
You are stuck in a mental model where everything naturally tends to "fall to the ground". This may be valid in the limited range of conditions you see on Earth, but you have to be careful extrapolating from that. Material calling from the interstellar medium could just as well push outward as inward. I don't immediately see a fundamental reason why it has to be inward.
So just as an object's altitude in a gravitational field exists as potential energy, two protons distance from each other exist as potential energy of fusion. To the extent that protons are separated/repelled from each other as hydrogen, they have the potential to fuse into heavier particles. So when the fusion process merges them and releases energy, the potential energy in their separation/repulsion is expended, no?
No. The energy from fusion does not come from potential energy due to their repulsion. If you think about that, you'll see it doesn't make sense. We talk about potential energy for gravity, but gravity is attractive, not repulsive. It is fair to say that two hydrogen atoms before fusing have some sort of "potential energy", but this would be driven by the attractive strong force, and not the repulsive electromagnetic force.
Ok, thanks. Does this present an argument or are you just clarifying the details of how it works?
Just clarifying how it works. Important so we can apply the lessons properly.
So fusion just slowly shifts outward due to increasing volume of helium at the core?
For the red giant phase, yes. When stars leave the red giant phase, things get more complicated. Stars can go on to burn helium, so you can have a helium-burning core with a hydrogen-burning shell, and for massive stars, they can go on to fuse heavier elements, so you end up with a sort of onion layer with heavier elements being fused further down, and lighter elements being fused in shells.
I was thinking along these lines, but I don't know enough about how the internal structure of particles is defined except for that various levels of sub-atomic particles are defined, like quarks and leptons. I don't understand those, though.
I can explain degeneracy pressure if you are familiar with the Heisenberg uncertainty principle. Heisenberg said that the more certain the position of a particle is, the less certain its momentum. If you squeeze a ball of matter enough, the space available for every particle decreases. If you do it enough, you can reach the point where Heisenberg's uncertainty principle is dominant and the small confined space for each particle means that there is a very large uncertainty in their momentum. If momentum covers a wide range of values, that means that the average momentum must be high, which translates into high pressure. This is the sort of pressure that keeps a neutron star and a white dwarf from collapsing. Notice that the argument has nothing to do with temperature, so when they cool down they don't shrink.
Interesting. Is there an assumption of minimum volume of particles?
I'm not 100% sure I understand your question. But perhaps some of what I wrote in the previous paragraph is related to what you asked.
I know, but if the contents were not gas but heavy elements, they wouldn't fuse, would they?
If they were higher than iron, they wouldn't fuse. Iron is the limit (the most stable element).
How so fast?
As I understand it, the origin of super massive black holes is a bit of a mystery because they happen so early. The answer probably requires that we understand dark matter, which is responsible for most of the gravity, and which we don't understand well at all.
If all orbits were non-decaying, how would stars ever congeal in the first place? Friction? Why would friction ever completely disappear in a galaxy/solar-system?
Yes, friction. If it weren't for friction, all orbits would be non-decaying. Friction in a proto-solar nebula is hugely higher than in the solar system today, or the typical interstellar medium. Technically it is not zero, but the time scale for it to have any effect is probably thousands of times the present age of the universe. It is at a point where you have to begin to wonder if other factors like gravitational waves, or disruptions from other stars, or planet-planet interactions, or the expansion of the universe might be more important.
Ok, no matter. Then they will fall into another gravity well eventually, no?
Not necessarily. I don't see an obvious reason why planets necessarily have to collapse into a larger object at some point.
But will the galaxies not coalesce into black holes prior to their heat death?
I doubt it very much. Especially for galaxies. In the case of galaxies you can't even invoke friction from the interstellar medium because that medium is part of the galaxy too and it is in orbit around the center of mass, just like the rest of the galaxy. Why should the galaxy coalesce into a black hole?
Likewise, as they coalesce doesn't their average level of gravitation increase? If it does, couldn't that cause the appearance of expansion as the OP suggested?
No. The gravitational force you see does not change when things coalesce. At a distance you cannot tell the difference between the gravity from a 1-million solar mass black hole and a globular cluster with 1 million sun-like stars. Finally, I don't understand how gravity can give the appearance of expansion. That really doesn't make sense to me at all.
I was under the impression that this is a pretty far-fetched possibility. Clusters of galaxies will probably separate... but our solar system, our galaxy, and even our galactic cluster should hold together regardless of the expansion or 'dark energy'. Is there evidence that the cosmological constant is actually increasing over time?
You don't need an increasing cosmological constant for this, and I am not aware of anyone suggesting that the cosmological constant is changing in any way.
You can roughly think of the cosmological constant as an acceleration term. If space expands with a constant acceleration, then the rate of expansion will increase quadratically without any bound, and at some point the expansion will become significant at the scale of a galaxy, and then at the scale of a solar system.0
Your point is ... ?
I think he's trying to argue that we do not exist. ;-)
However, Time did not begin as there was no event prior to Time that would announce, or could present, a start.
2. It is physically possible to reach the beginning of the universe - at ANY time whatsoever. By travelling at the speed of light - and some objects can do that - we become one with the conditions present at the beginning of the world.
Huh? What are you talking about? Travelling at the speed of light will not take you backwards in time.0
Gas pressure is the result of kinetic energy of the gas particles colliding with one another correct? Likewise, the distances of planets and other satellites orbiting a star, or stars orbiting the center of a galaxy are also due to the kinetic energy working against gravity, correct? So is it really such a stretch to view orbital distance/velocity as being similar to gas-pressure in creating the volume of a solar system or galaxy?
Yes, it is a very big stretch, and it is wrong. Let's go over this slowly: (1) Yes, gas pressure is the result of particles colliding with each other. (2) An orbiting body has nothing to do with anything colliding with anything. An orbiting body is basically on a free-fall trajectory that takes it around the star. It is not hitting anything. At the same time, the particles inside a gas are not in orbit.
Ok, the planets are stars are not exchanging momentum due to collisions the way you would expect particles in a gas to do, but their velocity nevertheless produces an expansive effect, no?
Saying "an expansive effect" is a very vague term. It has no clear meaning. This is the sort of thing that can make your physical thinking go in weird directions. The kinetic energy of a planet does not "expand" anything. An orbiting body is basically on a free-fall trajectory, with a centripetal acceleration corresponding to the gravitational force.
If it helps, imagine a toy universe where all the particles are point particles, and there are no electromagnetic forces. In this universe, nothing ever "touches" anything else, matter just passes through (point particles never collide) and there is no friction. Imagine that you magically transport the sun to this universe. What would it look like? Well, in this universe there would be no gas pressure, and no friction, so all the particles would simply be in orbit around their common center of mass. There would be no friction to make matter spiral toward the sun. In this universe, the sun's particles would stay in orbit forever and it would never coalesce into a white dwarf. What makes stars work like stars is particles hitting each other. This is the friction that can make things spiral inward, and it is what makes the gas in stars not behave like planets in orbit. The friction between the gas particles makes the gas coalesce, but the kinetic energy imparted by particle collisions makes the gas expand.
Does this help at all?
I don't know the conditions that caused the big bang to eventually form matter, but the fact that hydrogen fuses into heavier elements makes it possible to view gravitational coagulation as a catalyst for fusion.
I have no idea what you mean by "gravitational coagulation", but you are making a very fuzzy connection between gravity and fusion without stopping to think about how it actually works. If you do that, you should expect to reach wrong conclusions.
Thus, the fact that the big bang dispersed energy/matter broadly and with relatively even consistency amounts to a type of energy-potential. In other words, gravity only has the ability to induce fusion because matter was spread evenly so the spreading itself was the fuel for fusion to occur in a slow-crescendo as gasses coagulate and eventually reach a level of compression to "ignite."
We do have a concept of gravitational potential energy, which you probably remember from school. Gravitational potential energy is indeed the source of the kinetic energy that eventually allows protons to be stripped of electrons, and later, to overcome the electromagnetic repulsion between protons, which is a necessary step for fusion to occur. But again, it is better to think about what the mechanism is, rather than just making a fuzzy jump from gravity to fusion, because not everything that has gravity will have fusion. Planets don't do fusion for example.
I knew that, but thanks. Eventually they will become black holes, though, to the extent that they will eventually be pulled into another black hole, correct?
No. There is no reason why this should be the case. There is nothing special about a black hole that makes things necessarily fall into it. Just like you wouldn't say that Jupiter will necessarily, one day fall into the sun... Why should it?... Makes sense?
Stars consume dispersion of protons. Protons separated into hydrogen atoms are more widely dispersed than protons that fuse into helium and larger nuclei. So stars literally consume inter-proton repulsion (however they are repelled).
I cannot think of any sense in which "stars consume inter-proton repulsion". The electromagnetic force doesn't go away, and it is not the source of energy for stars. Fusion provides energy thanks to the strong force. The strong force is attractive, but short range. For very short ranges, it is more powerful than the electromagnetic repulsion. If the protons have high enough kinetic energy, they will be able to get close enough for the strong force to take over. This is what powers fusion (in simplified terms).
The energy that sustains a star at a relatively large volume keeps a good deal of its contents at pressure-levels that slow down the fusion reaction (an assumption, admittedly, am I wrong?).
Fusion only happens in the stellar core, which is about 1/6th of the star. The interplay between fusion rate and pressure is a bit different from what you suggested. If the fusion rate increases, the pressure increases causing the core to expand. When it expands, it cools down (remember the ideal gas law saying that pressure is proportional to temperature). This means that the particles have less average kinetic energy, and thus fewer of them are able to tunnel through the Coulomb barrier. This is (in simplified terms) how fusion is kept stable.
So, as they consume their fuel, they eventually collapse and sometimes supernova or red-giant as a result of the sudden condensation (this is something I haven't read about for a while so I could be mixing some things up).
All stars become red giants, and this has nothing to do with core collapse. Neither red giants nor supernovae have to do with condensation. A red giant happens when a star starts to run out of hydrogen fuel at the core. It builds a core of helium that is not doing any fusion, and it has a shell of fusing hydrogen. To continue burning, it needs to have a very high pressure + temperature at the core, which makes the core generate a lot of energy, which causes radiation pressure, which makes the star expand.
When they finally consume what's left of their fusion potential, they collapse into either white dwarves, neutron stars, or black holes if they have sufficient mass.
To be precise, the term collapse is only really appropriate for neutron stars and black holes. The process of becoming a white dwarf is more gradual, non-violent, more like a slow contraction than a sudden collapse.
So apparently there is something collapse-resistant in matter to prevent the cooled stellar matter from collapsing smaller than the Schwarzschild radius in some cases.
Electron degeneracy pressure keeps a white dwarf from collapse, and a neutron degeneracy pressure keep a neutron star from collapse. In 99.9% of the cases, the star does not collapse into a black hole. Degeneracy pressure has to do with quantum mechanics, and is not related to the temperature of the object.
However, there seems to be something about the gravitation-levels of a certain amount of matter that does causes the matter to collapse/compress beyond that radius, at which point you get a black hole.
For all degenerate stars (white dwarfs and neutron stars), when you increase the mass, the star actually shrinks, increasing both density, gravitational attraction, and the degeneracy pressure. You can show that, as you add mass, you reach a point where the contraction causes the gravitational attraction to increase faster than the degeneracy pressure. This is the point where you get a collapse.
Can any of this be applied to something that isn't a star?
Anything that has enough mass and density for the above processes to take place, WOULD be a star. After all, at the most basic level a star is just a really big ball of gas with enough mass that fusion can take place.You mean like if elements too heavy to fuse coagulated into a massive, dense lump?
The only elements that cannot fuse are those heavier than iron. If you somehow managed to get a big enough ball of lead and compress it down enough, it would form a white dwarf. But keep in mind that the elements bigger than Helium make up less than 1% of the universe, and the elements bigger than iron are a very small fraction of that, how exactly would you expect to pile and compress a ball of lead? In practice, the only way to make something degenerate like a white dwarf is through the usual star-based process that we are all familiar with.
Are there any galaxies without black holes at the center? I would guess that very young galaxies would have yet to develop black holes in the center.
No one knows for sure, but it is believed that most galaxies have super massive black holes at the center, even fairly young ones. The super massive black holes appear to form surprisingly early.
However, it makes sense that galaxies are slowly coagulating into smaller areas with denser centers. Could you have a galaxy where the contents reached a point of non-decaying orbit around the center?
Why does that make sense? What do you mean by coagulating into smaller areas? A galaxy is not spiraling inward if that is what you mean. ALL orbits are non-decaying unless you have some sort of friction (for the pedantic reader: please ignore gravitational waves).
In that case, could the stars run out of fuel, collapse, and continue to orbit without falling into the center?
This is the default behaviour. Except that most stars don't collapse, they just gradually form a white dwarf.
My impression is that gravity always continues to drive coagulation of matter dispersed by the big-bang in one way or another.
This would be wrong. Ignoring some details with gravity waves that really don't matter, once something is in orbit it just stays in orbit unless friction makes it spiral inward. Earth is not spiraling toward the sun.
Why wouldn't the solar system shrink once the sun goes out? Won't the planets slowly decelerate as they encounter occasional friction from various sources? Doesn't solar wind produce a certain amount of thrust for everything orbiting the sun?
The solar wind would push things outward. If you are going argue solar wind, you would be arguing that orbits should expand. Btw, when the sun enters its giant phase, it will lose significant amounts of mass and this should make the planet orbits expand gradually.I know this isn't much, but what could prevent the planets from encountering friction for the rest of eternity? If they are slowing down due to friction, what would prevent their orbits from decaying if there was no thrust to counteract the friction-deceleration?
I want to be very careful replying to this... If you look at the really long term (as in, several times the age of the universe), you can consider the tiny friction in the solar system as a factor that could make the planets or a whole galaxy spiral inward, but if you are going to look at that long term, you have to consider whether the expansion of the universe might not take the same solar system or galaxy and spread it apart before it has a chance to coalesce. If you wait long enough, the expansion of the universe should eventually tear everything apart (except maybe black holes). But if you wait long enough, even black holes will evaporate away by Hawking radiation, so in the really really absurdly long term you should have a universe that is nothing more than a very thinly dispersed sea of elementary particles. This is known as the "Heat Death" of the universe.0
This is a general comment for the whole thread: You need to realize that there is no "down" in space. You are imagining that gravity accelerates things "down". In space, gravity as you know it would accelerate things toward each other, meaning that either the expansion is slowing down or the universe is contracting at increasing speed.
Dark energy is the name we give to the phenomenon that the universe is not only expanding, but accelerating away from each other, opposite to our regular notion of gravity. Dark energy is just a name we give to something we do not understand. One possible explanation is simply that gravity is repulsive at large distances. This is the famous cosmological constant. But that is not the only possible explanation.
Next, I must point out that dark energy and dark matter are not the same thing. You have confused the two terms in your post. Dark matter refers to the phenomenon that the rotation speed of galaxies is higher than what can be accounted by the matter that we can see in them. Thus the idea that there is a very large amount of matter that we cannot see which is responsible for the increased gravitational attraction in galaxies. This has nothing to do with dark energy.2
Maybe not in the sense that gravity fields dissipate at the same rate from their center, regardless of what is emitting the gravitation. But what about the fact that black holes result from stars depleting their energy-generating capacity?
Do you understand in which sense black holes relate to stars running out of fuel? What could that possibly have to do with the expanding universe?
In other words, stellar matter maintains volume due to the energy that is being emitted from them. When their energy-output decreases, they collapse into a smaller volume. If you extend this effect to their surrounding space, you could look at entire solar systems and galaxies as having volume resulting from expansionary energy, the big bang being the original prominent one from which all space-time was set into motion.
That doesn't make any sense at all. You are seeing the universe as magic. You need to ask yourself, "WHY is there a connection between energy generation in a star and its volume?" The reason is that a star is a big ball of gas held up against gravity by gas pressure. Nuclear fusion increases the temperature inside the star, which by the ideal gas law will give you an increase in pressure, which is what holds the ball of gas that we call a star. Next to ask yourself if any of this applies to a solar system or a galaxy, and quickly you'll realize that neither one is a ball of gas being held up by gas pressure. Solar systems and galaxies have the shapes they do because the planets/stars are in orbit.
So as stars die and coagulate into increasingly gravitous black holes, they are consuming the energy and motion the big bang set in motion, no?
No. Stars work by nuclear fusion, not kinetic energy from the big bang.
And btw, the vast majority of stars never make black holes. The vast majority (like 95%) will make white dwarfs, and most of the rest will make neutron stars. Only the tiniest fraction of stars (those with masses above about 20 solar masses) will become black holes.I know I'm assuming a lot in this post, so please correct those assumptions that are misconstrued. Otherwise, I think the OP has a good point, no?
No, he doesn't. You and the OP need to think about what is actually happening physically. Don't just say "stars consume energy and become black holes". Ask yourself, what exactly do you mean by that?What energy do stars consume? Do most stars become black holes? Why are stars held up in the first place? Can any of this be applied to something that is not a star?
There is nothing about the physics that you don't know already. I'm sure you already know that stars are powered by fusion, and you already know the relationship between temperature and pressure. If you reasoned through I don't think you should come up with ideas like the solar system shrinking when the sun goes out.0
Why wouldn't it be the case that galaxy clusters are themselves galaxy-like formations with black-holes in their centers? I don't think the universe has a single center, but it would make sense that all black holes would be centers/drains of matter-energy swirling in, since they could theoretically have enormously large gravitational fields surrounding a volumeless point.
1. The universe has no centre.
2. There is nothing special about a black hole that turns it into some sort of vacuum cleaner sucking up a galaxy. From far away, there is absolutely no difference between orbiting a black hole with 1 million solar masses, or orbiting a stellar cluster with 1 million sun-like stars. Things only look different if you are very near the black hole, where you get an event horizon and probably an ergosphere, but these distances are insignificant compared to the size of the galaxy (a galaxy is about a trillion times larger in diameter than an event horizon or black hole).1
Yes giant cock roaches are improbable at best, but if arthropods were free of competition by mammals we might see giant arthropods but they wouldn't resemble what we think of as insects. Even the really big arthropods we have now do not resemble insects much.
This is correct. There is nothing wrong with having a large arthropod, but its physical proportions would be nothing like an insect with its tiny legs. The pictures you showed are a good example.
They would have to evolve a better breathing system for sure and have their legs under them like mammals. The exoskeleton would have to evolve some strength for them to get even a fraction of vertebrate size. The cube square law is hard to get around, lol
.....in a 1g environment. What if the alien cockroaches come from a 0.1g environment?
Then there is no atmosphere and any life is probably busy worrying about not being able to breathe. Mars has 0.4g and its atmosphere is 0.6% that of Earth, in spite of having half the solar wind flux.
But let's ignore the atmosphere issue. If you lowered gravity to 0.1g you would not get giant cockroaches. The cubic law catches up with you very quickly. How big could you make insects in a 0.1g gravity? about 10 times bigger (cubic / quadratic = linear with gravity). Imagine a cockroach that is 10 times bigger than ours. Yes, it's big, but I can still kill it with my foot. It is not a giant cockroach.1
Expanding Universe Illusion Theory
in Astronomy and Cosmology
Posted · Edited by DanielC
You started insulting me after I took a lot of time from my work to help you.
But you are, and you don't even seem to realize it. And if you are going to basically claim that modern astrophysics is wrong, you should at least know enough to realize that planets are not held up in space by pressure, and a few other elementary facts about physics. Read a textbook. Then make a coherent argument.
But you are not exploring anything critically. You are taking vague concepts that you heard somewhere on faith, without wanting to know how they work, and using that to develop your hypotheses. Instead of calling you an idiot, I very patiently explained a lot of elementary physics concepts like the fact that pressure is not the reason planets are in orbit. And then you accused me of taking formulas on faith. Don't you realize what you did? I have gone through the derivation of just about every key formula in astrophysics, because I want to understand at a deep level. On the other hand, you have a vague notion of things like pressure, which you take on faith, without knowing how they work. I did not insult you for that, but tried to explain, and in turn you accused me of taking things on faith. Between the two of us, you are the one who takes things on faith. You think you are thinking critically, while you just take vague physical notions on faith as if they were magic. How did you expect me to react? I think I deserve an apology.
(1) As I've said before, you don't measure distance in astronomy by looking at sizes. (2) Being underwater does not make it look like objects in the air are moving radially away from you at various velocities following a power law.
But water does *not* finely-tune its distortions to make it look like they follow some other set of physical laws. For example, it does not cause rocks that are geologically younger to look further away, or to look like they are moving faster than rocks that are geologically older. The distortion that water makes looks exactly the way you would expect from refraction. The bending of light that water causes does not discriminate between different types of rock on the sea floor.
Think about all the other things we use to tell the age of a galaxy: Young galaxies are bluer because they have more star formation. Young galaxies have a lower portion of heavy elements than old galaxies. Quasars are the brightest objects in the universe, and they only occur at extremely high redshifts. At the earliest universe, the youngest galaxies don't have definitive shapes like the Milky Way, you can see that they are just forming. Now try to imagine how the Milky Way could generate some sort of lensing effect that could discriminate these things to fool us. And then you have to explain why these independent measures of age are correlated (e.g. why stars with the highest star formation also have fewer heavy elements).
You'll need to define the words "similar" and "galactic scale". Being inside the Milky Way will not make supernovae look like they follow a power law.
I do not rely on faith, and I don't take GR as the be-all and the end-all. But to claim that it is wrong, you has to provide supporting evidence that is commensurate with the nature of the claim. For example, saying that GR is incomplete because it conflicts with quantum mechanics and it gives infinities inside a black hole is entirely reasonable. But if you were to claim (for example) that gravity doesn't make time dilate, you'd have to explain the results of many experiments that show that it does. And if you are going to claim that the expansion of the universe is not real, you will really have to explain all the experimental data that we have that tells us that it is, from the distance-dependent speed of galaxies, to the cosmic microwave background.
No response?!!! You asked if we had other ways to measure mass (you didn't say "star or planet") and I told you about the mass-luminosity relationship that we can derive from basic physics, the mass-colour (i.e. effective temperature) relationship, and about using light to count the number of stars in the galaxy. I also told you about tests of GR that do not involve the inverse square law, like tests based on time dilation, and how you can derive Newton's inverse square law from GR.
Also, Newton's inverse square law was never an article of faith, even before GR. Astronomical observations taken by Tycho Brahe, later studied by Johannes Kepler, indicated that planets move in elliptical orbits, following Kepler's laws. Then Newtonian gravity was able to explain these observations. Newton showed how you could derive all of Kepler's laws from an inverse square law. Then came GR, which made a whole set of new predictions, such as the precession of the periphelion of Mercury, the bending of light, the existence of white dwarfs, the existence of neutron stars, the expansion of the universe, the cosmic microwave background, and time dilation by gravitational fields. Please listen, this is an important point: These were all predictions. None of these things had been observed before Einstein. The GR equations predicted these things, and when physicists went to look for them, they found them, in exactly the way that GR predicted, to a very high accuracy. This gives us a great deal of confidence that GR is an apt description of gravity.
Doppler shift makes light look redder or bluer. The light curve of a Type Ia supernova has nothing to do with colour. A Type Ia SN gets very bright very quickly, and then gradually decays in intensity over a period of about 100 days or so. If you plot the intensity of the light against time, you get a curve with a particular shape. All Type Ia supernovae already have more or less the same luminosity, but by looking at the shape of this curve, you can figure out, within something like 2% error, what the luminosity of the supernova was.
Another way to measure distance is using Cepheid variables. This is a type of star that pulsates, so its luminosity goes up and down. The period of pulsation tells you its luminosity. Again, since Doppler shift only makes things bluer or redder, it cannot make the pulsation period look different. Cepheid variables and Type Ia supernovae are known as "standard candles". These are the things we use to measure the distance to far-away galaxies.
Doppler shift happens to every wavelength. We focus on visible light and radio because those frequencies are easier to observe. Gamma rays and x-rays don't penetrate Earth's atmosphere, so you need space telescopes for those. So you only use those frequencies for things that you really cannot investigate otherwise.