IM Egdall

Technically you can go backwards in time with math, but that doesn't happen in reality, time always just keeps moving forward, except maybe at the event horizon of a black hole to an outside observer.

And this is a fundamental problem with physics. The equations of physics show no preference for the arrow of time. So it is difficult to explain using physics why in reality time moves forward.

Entropy does imply a forward arrow, but it is a statistical concept and applies only to a large number of particles.

see http://en.wikipedia.org/wiki/Arrow_of_time

Interesting, if the sun was removed, would we continue to spin round nothing for 8 minutes?

Yes.

We would also "see' the Sun for the same 8 minutes or so.

I think time is a dimension simply because it's a coordinate, it's a coordinate you need to describe an object in reality. If you look on a graph, there's length and width and height, but more often than all of those is time.

So you can think of the 3 spacial coordinates, 1cm thick, 1 cm tall, 1cm wide, and occupies the relative time coordinate of say...13.5 billion years after the big bang, and counting, i.e. the time coordinate is changing all the time.

Yes. You are describing the four co-ordinates of an event in spacetime.

I think the fabric of space-time harbors both space and time, but I don't think the math actually shows the gravity actually = time. If I travel at 20 kilometers per hour, what's my gravity?

I did not say gravity = time. I said gravity is the warping of space-time. Per general relativity, both space and time are warped in the presence of mass/energy. The mass and energy of the Earth, for example, warps space and time in its vicinity. (Clocks run slower and radial distances are stretched.)

This warping of time and space causes objects to fall to the Earth, holds me in my seat as I type this, holds the Moon in it orbit around the Earth, etc. In short, all phenomena we attribute to "gravity" are the result of the warping of space and time (spacetime curvature). This is what the mathematics of general relativity shows.

Gravity alone affects DM normally, not weakly. One might say that particles affected by the mechanics of all four fundamental forces strongly clump together forming the objects we know, however DM is only affected by gravity and weakly clumps together, forming diffuse clouds.

http://www.physorg.c...s176457990.html

http://arxiv.org/pdf/0903.0101.pdf

These links describe how in the early universe the density of DM was perhaps enough that "Dark Stars" (stellar objects) did form and that Weakly Interactive Massive Particles (a candidate for DM) can collide and annihilate creating energy that would produce light and heat like more common stars.

So the reason DM does not form stellar objects from gravity alone is due to its density at present.

Fascinating! Thanks for the clarification on "weak" clumping and the dark star links.

Contemporary Science vs. Common Sense

 

The cosmos is both eternal and infinite.

I believe modern cosmology leans toward the "cosmos is infinite" idea. But per Einstein's general relativity, even an infinite cosmos can expand.

As to an eternal cosmos, it may very well be. We just don't know. Since general relativity fails at time zero of the big bang, we cannot project to before the big bang. Did time begin with the big bang or was there time before the big bang? We don't know. So an eternal cosmos remains an open question in our current understanding.

As to your saying it is all a waste of time, I totally disagree. The fact that some brilliant human minds on this tiny planet somewhere in the vast cosmos have developed a scientific theory on the creation and evolution of the universe which is supported by empirical evidence (lots of it) is extraordinary, to say the least. Yes we only observe a tiny portion of the universe (we think) and yes, the big bang theory may be subject to future modification and change (like any scientific theory). But all-in-all, I for one am thankful to be alive in this age of wonder and cosmic discoveries.

Space has always been expanding as long as the universe has been around, also time has always moved forwards as long as the universe has been around.

 

Einstein linked space and time in his view of space-time, maybe the universe expanding and time moving forwards are linked?

 

Gravity causes objects to accelerate, get faster with time, as space-time gets warped.

 

Thoughts?

Gravity is the warping of space-time. They are one and the same.

I believe the use of time as the "fourth" dimension started with the spacetime physics of Poincare and Minkowki in 1907 or so. And it is rooted in the concept of the spacetime interval.

Einstein showed in 1905 that time and space are relative -- the time interval and space interval between two events is different depending on the (uniform) motion of the observer.

Poincare and Minkowski showed that a combination of time and space called the spacetime interval is absolute. It is the same for all observers, no matter what their (uniform) motion. From this a new set of mathematics was developed in four dimensions -- three space and one time. See link:

http://en.wikipedia.org/wiki/Spacetime

It's not the data I dispute it is the interpretation.

First a little logic:

 

Before something can change, before something can act or be acted upon, it must exist.

 

This is a rather simple axiom, logically self-evident since any who might dissent must believe in things that don't exist. Existence in the absence of change is possible, change in the absence of existence is not. The fact that existence is required in order for change to occur explicitly means cause and effect is a function of (derived from) the phenomenon of existence. This is a No Brainer.

 

Existence is not a function of time/change/cause and effect, and since it is not temporal in nature the cosmos didn't "BEGIN". Any version of BigBang would have led to an entrophy death an eternity ago - even the cyclical model. If light is comprised of massless photons which would not be retrieved by the forces of gravity, then unless the Universe is entirely coated with a layer of black holes like a chocolate dipped ice cream cone, each "Big Crunch" would still have been plagued by an energy leak that would lead to a much slower - but ultimately inevitable - entropy death conclusion. And it would have happened an eternity ago.

So what interpretation do you propose which matches all the observations?

If anything you do allows you, in principle, to tell which slit an individual electron went through, then there will be no interference.

What's the difference between "combine" and "act separately" in this context, anyways?

The satellite clocks show a net (or combined) effect of both time dilation and gravitational time dilation.

Four fundamental forces are present in the universe, gravity, electromagnetism and the strong and weak nuclear forces. Traditional matter is governed by all of these forces. The strong force binds quarks into atoms. The weak force causes certain atoms to decay. The electromagnetic force binds atoms into molecules. Gravity causes atoms and molecules to form larger structures like pebbles and super galaxy clusters. Dark matter particles are not bound by the strong force into atoms, do not decay radioactively by the weak force and do not have an electromagnetic charge. These particles only clump together weakly through gravity.

Ya, I am aware of all this. My question was not about dark matter and strong force, weak force, or EM force. It was about dark matter and gravity. I was asking for a good link which explains the "weak" clumping of dark matter due to gravity.

Does the combination of Time dilation and Gravitational time dilation create an combined effect or do they act separately?

They combine. For example, clocks on GPS satellites must be corrected for both effects:

Time dilation: Atomic clocks on board GPS satellites run slower than clocks on Earth by about 7 thousand nanoseconds per day -- due to their motion relative to the Earth.

Gravitational time dilation: The satellite clocks run faster than Earth surface clocks by about 45 thousand nanoseconds per day -- due to their higher altitude.

Taken together, there is a net gain of about 45 -7 or 38 thousand nanoseconds per day. Since GPS needs an accuracy of 20-30 nanoseconds to work, the combined effect must be taken into account.

See link: http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html

<br clear="all"> http://www-astronomy.mps.ohio-state.edu/~pogge/Ast162/Unit5/gps.html

I have done some reading. 40 years worth and it depends on whose version you wish to quote - there are all flavors.

Cite me ANY BB model that envisions an INfinite amount of material or an INfinite volume in the Universe.

They cite the expansion model as proof of the expansion model.

It reeks of self serving reverse engineering.

Do YOUR homework. And think for yourself instead of parroting the conventional lore.

It wasn't that long ago that scholars of your caliber were debating over how many angels could dance on the head of a pin.

Obviously you have no specifics to discuss, so I guess a general denegration is the best you could do.

If the known universe - no, lets say a volume of the known universe taken to a power of septemdecillion - were to expand by only a billionth of a micron each billion eons, the universe would have suffered entrophy death an eternity ago. Existence didn't begin. It is not a function of cause and effect.

The big bang model is the best theory we currently have on the creation and evolution of the universe. Why? Because of all the evidence from a number of independent observations which agree with its predictions. See link: http://en.wikipedia.org/wiki/Big_Bang#Observational_evidence

If you challenge the theory, then please give us an alternative theory which also fits with observations and offers new predictions which can be verified.

the clumping via gravity also needs a way to dissipate the energy of the in-falling matter - normal matter generates heat; dark matter does not have the necessary interactions to do this and thus no overall concentration of matter occurs. that said dark matter does seem to occur in filaments and strands on a very large scale

Hmmm. Very interesting! Thanks. Do you know of a link where I could get more info on this effect where dark matter does not tend to form into stellar objects?

Although there is a lot more dark matter than ordinary matter, the dark matter is much more spread out, so that within the solar system it has a much lower density.

 

http://www.universet...e-solar-system/

 

The above may help.

Ya I thought it was something like that. There is so much space between stellar objects. The link you provided is very helpful . Thanks.

I still have a question though. Why is it dark matter doesn't clump due to gravity like ordinary matter into dark matter stellar objects?

So, based on the motion of stars in galaxies and galaxy cluster motion etc., there is roughly 5 times more "dark matter" than ordinary matter in the universe. No one knows what this dark matter is. But, presumedly, it is in our solar system. So how does it affect the orbits of our planets around the Sun and moons around the planets, not to mention comets etc. ?

How is it that we can explain these orbits and motions to such great accuracy using general relativity and only the masses of the Sun, planets, moons, etc? These do not include the effects of dark matter. If there is 5 times as much dark matter as the ordinary matter which makes up our stellar objects, why does it not affect these motions more?

Edited to fix my dumb typos.

I am pretty inept at this, but I still don't know how to put web links into my blog. I put in the URL address in my text, highlight it, and then press the blue LINK button. It does some code thing to the address, but when I do a Preview, there is no link. And how do I fill out the form that comes up? Any help is most appreciated.

Here's how I think it goes. I know this explanation is not rigorous, but I think it gives the gist of what is going on.

Per general relativity, spacetime curvature is the warping or change in spacetime due to the presence of mass/energy. The mass and energy of the Sun, for example, warps both time and space in its vicinity. This warping is what makes planets orbit the Sun. So so-called spacetime curvature is gravity itself.

The word "curvature" is a mathematical term. I don't think it should be taken literally as something curving. In gr, it refers to the generalized spacetime interval (the metric) changing globally in a gravitational field.

Space warp (distance change): Imagine two points in empty space with a certain distance between them. Now place the Sun between the two points. Now, as seen from far away, the distance between the same two points is greater! One can think of this as space having been stretched by the mass/energy of the Sun.

Time warp (time interval change): Imagine a clock in empty space. It runs at a certain rate. Now place the same clock near the Sun. It now runs slower. Time is slowed by the mass/energy of the Sun.

Taken together and represented mathematically by the generalized spacetime interval, this slowing of time and stretching of space in the Sun's presence, this warping of spacetime is spacetime curvature is gravity.

I hope this helps.I welcome comments and corrections.

Are you thinking of the amplitude? They can be positive or negative. You add the amplitudes then square the result. This is the probability of finding the particle in a certain location. And since you square, it is always positive.

You can't conclude that mass increases and time slows from this factor of two. Time dilation completely explains the slower oscillations in this example and the frequency varies as [math]\omega = \sqrt{\frac{k}{m}}[/math], so it wouldn't change by a factor of two anyway, if the mass changed it would slow by the square root.

 

As D H already mentioned, the "mass increases" concept comes from not separately accounting for translational KE. It's from using m=E/c^2, where E is the total energy and m is the relativistic mass, rather than [math]E^2=m^2c^4 + p^2c^2[/math], where m is now the rest mass, which is invariant. Or in terms of momentum, you have [math]p=\gamma mv[/math] and you are redefining mass as [math]\gamma m[/math] , making it velocity-dependent.

 

In the oscillating astronaut-on-a-spring example, if you use relativistic mass you have the curious circumstance of mass varying with time, and being dependent on the orientation of the oscillator.

Thank you for the enlightenment.

Are the tidal forces of a black hole that cause spaghettification strong enough to rip apart the bonds holding the atoms of the the spaghettified matter together? If so, what about the bonds of the nuclei? Can any non-elementary matter make it to the event horizon of a Black Hole?

 

I'm thinking that it might be strong enough to cause fission, but not strong enough to break down all matter into elementary constituents since the amount of energy it takes to pull out a quark from a bound system is enough to create a partner for it to bind with.

I believe the spacetime curvature (gravity) of a black hole is so strong it overcomes all forces, including atomic bonds and nuclear bonds. But i am not sure about your quark question.

For just the basics of the strong force, take a look at the Particle Adventure http://particleadventure.org/strong.html

Okay so my theory on time travel is; when approaching the event horizon of a black hole( if you can even make it that far without whatever space craft your traveling in being stretched to it's absolute limit then being torn apart and swallowed) time seems to slow down untill it eventually almost seems to stop, but in reality, in the event horizon times seems to move at normal speed inside of it.But, on the outside looking in it looks as if your not moving at all. The laws of space time break down at the event horizon breaks down becuase there virtually is none. So, when you got back to earth you'd be in the future because you were basically in a place where time stopped or just didn't really exist, but on Earth, everything was still moving and time did work. I'd really like to hear opinions on this topic!

A similar kind of time travel happens whenever you change altitude here on Earth. Per general relativity, time runs slower on the surface of the Earth than it does on the top of a mountain (by a very small amount). So if you live at sea-level, when you go to the top of that mountain you arrive there a little bit into the future.

Okay, so energy is equal to mass times the speed of light squared. The problem with reaching the speed of light in a spaceship is that the more energy you gain, the more mass you will gain and you will slow down. http://zidbits.com/2...speed-of-light/

So why does the mass affect the spaceship in space if you are weightless?

I found this example helped me understand how mass increases with speed per special relativity. Hope it helps you.

Astronauts in space are effectively weightless, but they still have mass. They use a contraption called an Inertial Balance Spring Scale to determine if their mass is changing during their time in space. This is a seat set on springs. An astronaut sits on the seat, grabs onto the rails, and pulls him or herself down --compressing the springs. Then the astronaut lets go. The spring scale chair then oscillates up and down as the springs release and compress. The more massive he/she is, the slower the spring scale oscillates.

Now imagine a rocket in outer space with a spring scale and astronaut inside. Say the rocket flies by you at 87% the speed of light. Per special relativity, from your point-of-view time inside the rocket goes at half the rate as your time (time dilation). So you see the astronaut on the spring scale oscillating at half the rate than if the rocket were at rest. Since the spring scale oscillates slower by a factor of two, you conclude the astronaut has twice the mass than at rest.

This is a relative effect. From the astronaut's point-of-view (reference frame), the uniformly moving rocket is at rest. So his/her mass is unchanged. But to you, the rocket is moving. So you see time on the rocket running at a slower rate and the astronaut's mass as greater.

And the greater the rocket's velocity with respect to you, the more you see its time running slower, and the greater the astronaut's mass. The effect is not linear. It goes as the square root (1 - v ^2) where v is the velocity as a percentage of the speed of light. As the rocket's velocity, v approaches the speed of light, its mass approaches infinity.