IM Egdall

Another way to look at it is this: Stay-at-home Steve is on Earth. Arianna takes a rocket trip to a distant star and returns to the Earth. When they compare their watches at the end of the trip. they find Arianna's watch on the rocket has run slower than Steve's on Earth. This assymetry is due to the fact that Steve has stayed in a single inertial reference frame all along. But Arianna in the rocket has actually been in two inertial reference frames -- one going away from Earth, and the other returning to Earth. It is this asymmetry experienced by Arianna which results in her clock runnung slower than Steve's.

Now you may try to argue that to Arianna, Steve had moved away from the rocket, and then he has moved towards the rocket. But this is not so. Steve felt (measured) no change in speed or direction. (A simple accelerometer would verify this.) But Arianna had to change inertial frames, and in doing so, she did feel (and measure) a change in speed and direction.

In the simplest analogy, it is as though Arianna jumped from her outbound uniformly moving ship to an inbound uniformly moving ship. (This is of course a simplification.) Steve did not have to do anything of the sort. He remained in the same reference frame -- the Earth -- the whole time.

You can show the slowing of time occurs for the rocket observer and not for the Earth-bound observer using special relativity (time dilation) and the doppler shift. If you want to see the details, go to marksmodernphysics.com then click on ITs Relative, Archives, and The Twins Paradox

Hypothetical theory allowing for the transmission of information to be passed between two points at greater than the speed of light.

 

Or a theory about string (but not a string theory).

 

 

Imagine a piece of string one au in length being held taught by two opposing spacecraft attempting to fly in opposite directions.

 

If I cut the string in the middle, the two spacecraft will fly apart almost instantaneously, whereas from the middle, it would take four minutes for light to reach either spacecraft.

 

alternatively I could just push down in the middle, both ships should instantaneously feel increased force pulling them backwards, faster than it would take light to travel between the point of depression, and either spacecraft.

 

Take that relativity!

 

Disclaimer!!!

 

I appreciate relativity precludes a number of physical properties because of their contradictory nature (such as a perfect rigid body), and guess that the tension carried in any conceivable substance might be offset over large distances by an element of stretchiness?

It seems to me the disturbance caused by cutting or pushing down on the string will propagate at a speed less than the speed of light. The string is, after all, made up of molecules, and the disturbance to molecules in the center has to be transmitted outward in both directions to adjacent molecules. This takes a finite amount of time which is less than the speed of light. So no contradiction with special relativity.

Ahhh OK.

 

I don't pretend to fully comprehend it but bringing 'energy' (more specifically concentrated energy in the form of mass) into this discussion sort of adds a new 'dimension' of understanding for me.

Per E=mc^2, mass and energy are equivalent. In other words, both mass and energy produce the same physical effects. So both mass and energy produce gravity. And per general relativity, gravity is spacetime curvature (the global warping of space and time by mass/energy).

The mass of the Sun, for example, produces spacetime curvature (gravity) in its vicinity. The energy of the Sun (its photons) also produces spacetime curvature (gravity) in its vicinity.

There are various types of popularizers. There are a few great scientists -- Steven Weinberg, Richard Feynman -- who have given lectures and written books for popular consumption that do a great service and accurately reflect the beauty and wonder of science. There are great scientists, Stephen Hawking, who have written excellent books (A Brief History of Time) but later succumbed to commercialism (The Grand Design) and pursued popularizations apparently for money. There are hacks, Michio Kaku leaps to mind, who peddle all sorts of tripe for personal gain and ego satisfaction.

 

I laud the former and decry the latter. I pick and choose among the works of those in the middle.

 

Hurray for Feynman and Weinberg. A pox on Kaku and (now) Cox.

I agree that Hawking's A Brief History of Time is a very good book, but I found few lay people could follow it. My brother-in-law calls it the best seller that nobody read. I also agree that his book The Grand Design was pretty bad. I use Feynman's classic QED, the Strange Theory of Light and Matter in my quantum course for lay students. It is wonderful.

I also use Brian Greene's The Elegant Universe and The Fabric of the Cosmos in my courses. I would be interested to know what you think of Greene's popularizations.

I like to think about the universe like this:

 

You cannot be at the edge of the matter going away from the center of the big bang at light speed because you can always point a beam of light over that edge. If the laws of physics are the same everywhere and there is no special place in the universe like a place where the big bang happened then this implies that the big bang happened everywhere at the same time. If there is something going away from something at light speed for everything in the universe then the universe is infinite. For every observer in the universe, the space gets progressively distorted the further away from him. Close to the 13.7 billion light years distance everything is going away from the observer at nearly light speed so it is nearly flat. So for every observer, the universe is a sphere with 13.7 billion light years radius where everything near the edges gets infinitely flat and infinitely dense and with infinitely slowed time so you can take this as the limit of the universe although the universe remains infinite nevertheless.

 

Are my thoughts correct?

 

As a speculation: if there is infinite mass and density at the edges of the universe wouldn't that be the cause for the accelerating expansion since the gravity of everything on the edge will pull everything inside the sphere and eventually everything will end up on the edges. But everything is also always in the center of the sphere so the pull is always cancelled out... Thinking about this can make you crazy.

Here is my understanding. Yes, according to the big bang theory, it happened everywhere. The "explosion" was the expansion of space itself. But whether the universe is infinite or finite is still unknown.

The rule that nothing can travel faster than the speed of light through space is from special relativity. But per general relativity, space itself can (and does) expand faster than the speed of light.

Apparently, CERN has identified two possible issues in their faster than light neutrino results. One, a faulty optical fibre, would make the neutrino speeds less than reported. The other, an oscillator used for GPS timing, wouild make the neutrino speeds greater than reported. I guess we have to wait for further analysis to find out the total impact of these anomolies on the measurements. (The devil is in the details.) See link:

http://physicsworld.com/cws/article/news/48763

The error comes from the fact that the equivalence principle applies only locally, whereas Einstein used it in coordination with Newtonian gravity to predict an incorrect value for the deflection of light. If you think the equivalence principle is in error, by all means come up with a explanation for why experiment agrees with it so well.

Well said. I think this agrees with my earlier point. A beam of light across an accelerating elevator will bend. But by half the amount we would see in an equivalent gravitional field. This is because, as you say say, the EP applies only locally. In that sense, the EP is limited (I did not say it was in error). It does not take into account the geometry of space See link:

http://www.einstein-online.info/spotlights/equivalence_deflection

All the time, every day.

 

Maybe this is not your view, but when I read or hear people make flat-out claims like "global warming is a hoax" or statements like that, I ask "how can you be so definite, so sure in your statement -- is there no uncertainty in this?"

What I read (mostly) from the climate scientists are write-ups which include the uncertainties in the conclusions. (Like "with 90% confidence" or "90% likely). This seems to me to sound more like a careful scientific approach.

I think I get it:-

 

Maxwell calculated that the speed of light is invariant.

Michleson Morley proved it.

This meant that if nothing can travel faster than light then we need to use Lorenze transformation formulae for relativistic speed additions.

 

C is constant because of how we add up relative speeds.

Not quite:

Yes, Maxwell's equations say the speed of light is invariant. But physicists had difficulty interpreting the meaning of this. In 1905, Einstein proposed his light postulate - which in effect says no matter what (uniform) speed you are traveling at, no matter what speed the source of the light is going at, you measure the speed of the light beam as the same value (i.e. invariant).

No, Michelson Morley did NOT prove the invariance of the speed of light. MM just found no evidence for the ether. Their experiment said nothing about the invariance of the speed of light. (A number of later experiments, however, did verify the invariance of the speed of light).

C is constant because the speed of light, c is invariant. Einstein's formula on how to combine relative speeds obeys this principle.

No, he used the accelerating elevator though-experiment to demonstrate that light would, in fact, fall due to gravity (something that wasn't known at the time). He made no such calculations.

From Hans Ohanian's book, Einstein's Mistakes - The Human Failings of Genius, p. 226:

"(Einstein's) 1911 calculation of the bending of rays of light, which was based on the Principle of Equivalence, yielded a result half as large as the new calculation (in 1915) based on his new theory of gravitation. Einstein understood that the reason for this discrepancy was the warping of space, whereas the 1911 calculation had effectively included only the warping of time . . . (Thus) the bending of a ray of light in an accelerated box is half as large as the bending in a box at rest in a gravitational field.

" . . . in 1913, Einstein's friend and colleague Ehrenfest . . . had published a short paper presenting a general proof about the failure of the Equivalence Principle for the propagation of light."

As I understand it, Einstein deduced gravitational time dilation from the EP. From this, in 1911 he calculated the wrong-by-half value for the bending of light. By considering only the warping of time, Einstein's mathematics gave identical predictions as Newton's. (I do not believe he realized this at the time.)

This is patently false. A spaceship with the appropriate amount of acceleration is indistinguishable from a local gravitational field.

 

I'm guessing this is coming from the factor of 2 difference between the Newtonian and GR predictions about the deflection of light around the sun. I assure you this has nothing to do with a failure of the equivalence principle. In fact, it gives more credence to it.

Sorry, but I do not think you are right here.

Einstein came up with the EP in 1907. Based on the EP and his free-falling elevator thought-experiment, he calculated the bending of starlight as is passes very close to the Sun's surface. He got a value of 0.875 arcseconds. This is the same (incorrect) value predicted by Newtonian gravity. And it takes into account only the warping of time.

Then in 1915, with his new field equations of general relativity, Einstein revised his prediction to twice the amount: 1.75 arseconds. Experiments since have confirmed this value to extreme accuracy. (This takes into account the warping of both time and space).

MM showed that there was no variation in the speed of light detected relative to changes in direction/drift speed of the postulated ether wind. As the whole apparatus was on the earth moving at high speed through the ether and turned at the same time ; it is easily shown that each reading must be at different angle to the drift of the ether wind - at some points it must be parallel at others perpendicular. the speed of light SHOULD have described a sinusoidal variation as the angle with the ether wind varied as the apparatus turned - it did not have the variation. Variations would also be seen on a daily basis, and yearly - these were also missing. The simplest explanation was that the light did not require an ether to travel through. Basically MM showed that the absence of ether theory was a better fit to experimental data

Yes, MM failed to detect the ether. But it said nothing about the absolute speed of light.

This is from one of the articles that you provided in the link. This is what the IPCC states as uncertain.

 

Do so-called climate-change deniers talk about uncertainty in their conclusions? Please let me know.

The Equivalence Principle (EP) has its limits. The beam going across the spaceship will bend only half the amount of a beam in a equivalent graviational field. The EP takes into account only the warping of time, and in fact gives identical predictions as Newtonian gravity. General relativity gives the full effect due to both time and space warp -- which agrees with actual measurements of starlight passing the Sun.

Enter light. Maxwell's equations show that light meets the requirement of propagating at the same speed in all inertial frames. So do many experiments, starting with the well-known historical Michelson-Morley experiment.

As I understand it, the Michelson-Morley experiments said nothing about light propagating at the same speed in all inertial frames. The MM experiments were done in a single reference frame -- the light source, the interferometric apparatus the light went through, and the detector (film?) were all at rest with respect to each other. So the experiments didn't prove or disprove Einstein's light postulate.

If we are in a rocket flying to the sun at 0.75C, why would we measure light from the sun AND light from earth to be C. It can't be because "moving clocks tick slower" for both cases, can it?

Maxwell's theory says light is a continuously moving electromagnetic wave. The continuously changing electric part of the wave produces a continuously changing magnetic part. This in turn produces the electrical part. They produce each other.

The key here is continuously changing. Einstein imagined moving at the same speed as a beam of light (at age 16!). Buit if he did, the beam would appear at rest with respect to him. So then the electric and magnetic fields would be static -- not changing. So they would not generate each other, and the EM wave would not exist from his poiint of view. As someone said, a light beam must move to exist.

So, Einstein concluded, you can never catch up to a light beam. It always goes at the same speed no matter what your (uniform) motion.

Several different views were offered in this other thread linked below. You might find what you're after there. If not, just let me know and I'll try to help you find what you're looking for to help eliminate the uncertainty in your understanding.

 

http://www.sciencefo...30-year-trends/

 

In the meantime, this graphic gets to the heart of swansont's point:

 

 

Thank you iNow. The evidence in the graphic is clear and compelling. As I said, the more I learn about this issue, the more I am convinced on human-induced global warming and the urgent need for action now.

No, the MSU data does not show that. If you plot the data, you can fit a line to it, within the error bars, that shows warming. You cannot claim there is no warming if you can do that. It is a lie. You can also fit a line to it that is flat, which means you cannot claim that there was warming, either. Over such a short time scale, the data are too noisy to make either claim. But if you look at a longer data set, which averages down the noise, the warming is clear. One makes the "no warming" claim either by being incompetent or deceitful.

John B shows the data from 2000 to 2011 in post #209. Where may we find the longer data set chart you refer to. I apologize if you have already posted this chart.

May I please "kibitz" for clarification ? I understand, that "mass tells space-time how to curve; and curved space-time tells mass how to move" (Wheeler. Journey into Gravity & Spacetime). Er go, different mass distributions, generate different space-time curvatures. So, I understand, that in "gravitationally bound" structures, e.g. galaxies, space-time is non-expanding; whereas, in deep space between the galaxies, space-time is expanding. From this understanding, I would say, not that "gravity inside galaxies 'offsets' expansion"; but rather that bound objects have fundamentally different space-time curvatures, where-with-in the fabric of space-time is non-expanding.

 

Your use of the word "offsets" suggests some sort of "internal struggle", between a vaguely "Schwarzschild-like" space-time, attributable to local galaxy masses; and a Hubble-expanding "Friedmann" space-time, attributable to the global cosmological mass distribution. Is there such a "struggle" of competing factors, within the fabric of space-time, within galaxies ? The vaguely "Schwarzschild-like" space-time, inside a galaxy, as numerically calculated, in isolation, would presumably be vaguely "static" (on galactic scales). But, in real life, galaxies are embedded into the expanding space-time fabric of our universe. So, is your use of the word "offsets" an accurate description ? E.g. does the Hubble expansion "tug at the edges" of galaxies ??

My understanding is the expansion does "tug" throughout galaxies. It is pushing space apart within our galaxy right now. But gravity (spacetime curvature) is pulling it together within our galaxy. Gravity within our galaxy is much more powerful, so it dominates -- thus stopping the expansion of space within our galaxy.

See linkfor calculations on expansion within galaxies: http://answers.yahoo.com/question/index?qid=20110605063620AAapPXk

So

The source of the data explains this plainly. Instead of assuming malicious intent, go read the source.

 

Just because non-experts think that the term "adjusted" should be equated with the term "nefarious" or equivalent to "false, flawed, fudged, untrustworthy, etc.," does not mean the data is any of those things.

 

 

Here's the source. if you click this link there is a detailed explanation of all adjustment processes and why they are used. I've only summarized one final comment in my quote. The link is worth the look if you find yourself with questions about the adjustment process.

 

 

http://www.ncdc.noaa...ushcn.html#QUAL

 

 

 

I do not assume malicious intent. Far from it.

Thanks for the link, iNow. It shows the science behind the adjustments, which seem to me to be both reasonable and necessary.

Urgent why?

Because the potential impact of global climate change on human life (and other life forms) is potentially devastating. And the longer we wait to do something significant on a global scale, the harder it is to stop the consequences. And the more likely thousand or even millions of people will die due to our lack of action. And there may be some point of no return - when climate change is no longer correctable by human action.

Yes, here.

 

 

Frankly, I prefer the curvature factor in the form (1-2M/r), because it shows the influence of the Mass on the metric. The angle term is zero in case of a radial fall.

 

The point is that for r > 2M the sign of dt² is positiv and that of dr² negativ. Beyond the event horizon its just vice versa.

So, dt² and dr² change role at r = 2M. Its a consequence of the coordinate singularity at r = 2M.

 

It might be of interest that the mentioned coordinate singularity vanishes, if the Schwarzschild coordinates are transformed into Kruskal-Szekeres coordinates. Then the t- and r-coordinates remain timelike and spacelike.

Got it. Thanks guenter.What are the physical implications?

Time is not what you think, in my last week I have been posting on the naked scientist under artpiecemalpsso, on the topic of time and how the future and past are non existent as actual realm of time. As I envisioned the time realm of the past I envisioned that what the past was was nothing more then present moments played out with other present moments, a book that was writen one hundred years ago was in the present moment of existence, and every present moment of everyone who ever came in contact with it, how is it now that that book is right here in ever present moment and not back there in the past. The past is Ideas of the present moments it defines, how we saw what happened, how we told what happend, but all of that was done in present moment of time. The future is a projection of what we hope it to be, but the truth is that everything we do right here right now is in the present which defines everything that happens in the present moments that seem to matterialize from one to the other. We as humans have conditioned ourselves to believe that time is out there, in some other realm of existence, when in fact it all lies here right in this realm of reality. I call it the sphere of reality realm of constant non constact reactive time in the present moment. Although it changes it never advances past the point of present reality, what we do now is what we do now, and now and now. It seems as though my theory is bases deep in the imagination of man, a web of deception of time. I was caught up in it with my relevant time travel theory, all of which is published at artpiecemalpasso/worpress.com under Space, time, matter. Ultimatly I had to drop my theory of some ten years. Although I welcome comments I will only choose a few to respond to, I have been going non stop on the Naked scientist with this, and Im tired. When my will exceeds my malaise, I will respond. Thank you everyone for your time, Artpiecemalpsso

Suggest you read Brian Greene's book, The Fabric of the Cosmos. He presents an excellent physics discussion in lay terms on the nature of "time". It touches on some of the issues you raise. For example, per spacetime physics, an analogy for time is not a flowing river from past to future, but a block of ice with all of spacetime frozen and existing. He says we must think of all of time as "out there" just like space. Fascinating stuff!

P.S. Please divide your writing into paragraphs. It would make it easier to read.

a naive question probably,

 

obviously the expansion of the universe now in proportional terms is very very slow (would be interested to know how slow, how much further would an object exactly a billion light years away be after a year), but presumably even objects much closer together are moving away from each other and we could in principle observe the expansion of space? if the theoretical expansion between two points is below a planck unit how would it occur exactly?

Within galaxy clusters, gravity offsets the expansion. So the expansion is evident between galaxy clusters but not inside them. Thus the stars and planets etc. inside our Milky Way galaxy are not expanding.

See link for how fast the universe is expanding:

http://helios.gsfc.nasa.gov/qa_sp_ex.html#fastexp

I try to keep an open mind. I am not a climate expert, so I have to make judgements based on what others are saying. So far it seems to me human-caused climate change is real and doing something about it is urgent. This is based on reading Scientific American articles as well as those in Physics Today, this forum, and other places on the web, etc.

But I am still curious. How about John B's chart from NOAA on difference between raw and final USHCN data set? Does anyone have an answer for his statement that the raw data shows only a tiny increase in warming? How and why does NOAA "adjust" the data?

One can find this wording in some popular literature, but it is not correct to say so. The wristwatch of the freefaller shows still the flow of the time after he has crossed the event horizon. What happens in Schwarzschild coordinates is that the curvature factor is < 0 for r < 2M, which makes the t-coordinate spacelike and vice versa the r-coordinate timelike. So, these radial coordinates do interchange, not space and time.

Can you elaborate or give us a link on this please.

If there is a black hole in the centre of our galaxy, what effect would that have to our time on Earth?

There is a black hole at the center of our galaxy. But it is so far away that its effects on Earth are negligible.