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claycravens
2005-Jan-29, 05:37 AM
Does the Equivalence Principle apply to the acceleration in expansion of the universe?

antoniseb
2005-Jan-29, 05:58 AM
Originally posted by claycravens@Jan 29 2005, 05:37 AM
Does the Equivalence Principle apply to the acceleration in expansion of the universe?
That's a good question. I'd start by assuming no. What would you measure it against. No one part of the universe would feel the acceleration. If it is yes, allow for other effects to need to be accounted for on that scale. Also, for any one place, the acceleration of expansion is *very* slow, and relativity may not be an important consideration.

claycravens
2005-Feb-18, 02:49 AM
I love a theory that the expansion is part of large-scale spacetime curvature, where relativity plays the central role in not only the acceleration of the universe but also the expansion itself. Thus the reason for the question about the equivalence principle. I believe the theory may be consistent with evolution equations and would have predictions that could be measured, including that the acceleration of the universe increases substantially at far distances.

What do you think?

piersdad
2005-Feb-18, 03:12 AM
a foot note here
I read that when some scientists were reviewing all the measurements of the speed of light from a 100 years ago their methoids were accurate enough to stand up to present day measurements.
and they noticed that the average measurement then was slightly faster then than it is now.
the assumption then is the perhaps time itself is slowing down as the universe expands

Matthew
2005-Feb-18, 05:41 AM
I don't think methodology of 100 years ago would stand up against our methods today. Measuring distance independant of light hasn't improved much, but measuring time has improved considerably. Time is now measured with atomic clocks, 100 years ago I think the most accurate was a quartz watch (though that is only a guess).

piersdad
2005-Feb-18, 11:17 AM
agree that 100 years ago their methods would not stand up to our modern ones.

from what i vaguely remember their method was to send the light beam back a forth over a measured distance .
so timing and distance measurements could vary a lot

but just a thought
If the speed of light changes so does the speed of an atomic clock?

food for thought there

Shoemoodoshaloo
2005-Feb-22, 02:56 AM
but just a thought
If the speed of light changes so does the speed of an atomic clock?

Yes indeed. Atomic clocks in satellites that move faster than the rotaional speed of Earth have to be reset every few years.

400poundgorilla
2005-Mar-11, 03:41 AM
Piersdad,


I read that when some scientists were reviewing all the measurements of the speed of light from a 100 years ago their methoids were accurate enough to stand up to present day measurements.
and they noticed that the average measurement then was slightly faster then than it is now.
the assumption then is the perhaps time itself is slowing down as the universe expands

Do you think there is a proportional relationship between time and expansion?

Mild mannered
2005-Mar-15, 11:21 AM
Originally posted by 400poundgorilla@Mar 11 2005, 03:41 AM
Do you think there is a proportional relationship between time and expansion?
Though I am not a scientist I asked just this question a long time ago. It seemed obvious (to me) that if the Universe is expanding by stretching then light speed and time must change proportionally with that expansion (the Universe is getting thinner, less dense)

If the Universe is truly expanding and remaining roughly the same density then this would not occur.

Lastly maybe I'm wrong but if the fabric of the Universe is getting overall less dense then Time is speedding up! (Near Black Holes it is slow because of extreme density)

What ya all think is happening up (out) there?

Nereid
2005-Mar-15, 11:35 PM
But how could you ever tell?

SR has been so successful that length are now defined in terms of c (SI definition (http://www.simetric.co.uk/sibasis.htm)), and measurements of time are now (or soon will be) so accurate that comparisons between different locations will be all but impossible.

Several sets of observations have been made into whether the fine structure constant has changed over cosmological time (e.g. the last several billion years on Earth; the last 10 billions years or so in the universe) ... the best work is consistent with alpha being constant (to parts per million or billion per annum) ... which implies many fundamental constants are just that (at least since the era of the CMBR).

Mild mannered
2005-Mar-16, 10:45 AM
Originally posted by Nereid@Mar 15 2005, 11:35 PM
But how could you ever tell?

I have to agree - you probably couldn't.


which implies many fundamental constants are just that (at least since the era of the CMBR

Understand please I am not debating anything here - just wondering aloud.

If BB theory is correct and the universe was very compact at some point in the past then time them must have been incredibly dilated. It is unravelling with the expansion of the Universe. You might not feel it but I disagree that it is constant - relative maybe - even if the changes are are miniscule I think that the "speed" of time and light are relative to the square of the expansion of the Universe.

That is just my (lightweight) opinion - am I missing something?

Mild :D

Nereid
2005-Mar-16, 01:25 PM
Understand please I am not debating anything here - just wondering aloud.
Wondering aloud is good :D

If BB theory is correct and the universe was very compact at some point in the pastOK
then time them must have been incredibly dilated.Why? I mean, other than an intuitive feeling, why should 'the rate of time' vary according to the size, density (of the universe), or any other parameter?

am I missing something?
Probably; as I think I said earlier, most (all?) of the concepts we are discussing only have a meaning that is amenable to scientific analysis (cf philosophical waffling) within the framework of a (scientific) theory, or class of theories. I know it's hard to grasp the idea that everything we discuss wrt the universe, the Milky Way, the solar system, ... is 'theory dependant' (unless, as I said, we are merely speculating, or are waxing philosophical), especially as most of us (no doubt) are quite unaware that the concepts we use are so deeply soaked in theory.

Perhaps some history might help. Take atoms; we've all learned about the intellectual origin of the idea with the Greeks, and the scientific foundation laid merely a few centuries ago. We all happily talk about atoms (molecules, nuclei, electrons, ...) and rarely pause to think about theory and reality. Yet 'the atom' is a theoretical concept! For practical purposes we act as if they are 'real', we build computers and make hairspray as if they are 'real', etc ... and why? Because 'atomic theory' is good - it is internally consistent, consistent with other good theories in its domain of applicability, and consistent with good experimental and observational results, and so on. However, to an intelligent, educated person living in China in the 10th century, there were no 'atoms'.

It gets trickier to do the same thing with something that's both a technical term and an ordinary word with a long (linguistic) history (e.g. 'energy', 'heat', 'time'); the conclusion is the same though.

I hope this helps.

Mild mannered
2005-Mar-16, 04:50 PM
If BB theory is correct and the universe was very compact at some point in the past then time them must have been incredibly dilated.


Why? I mean, other than an intuitive feeling, why should 'the rate of time' vary according to the size, density (of the universe), or any other parameter?

When we discuss a black hole we assume that time dilation takes place close to the event horizon - in fact near any massive gravitational body - so why not near a dense early universe?

I do not understand this - sorry please excuse my ignorance

Nereid
2005-Mar-16, 05:47 PM
Originally posted by Mild mannered@Mar 16 2005, 04:50 PM

If BB theory is correct and the universe was very compact at some point in the past then time them must have been incredibly dilated.


Why? I mean, other than an intuitive feeling, why should 'the rate of time' vary according to the size, density (of the universe), or any other parameter?

When we discuss a black hole we assume that time dilation takes place close to the event horizon - in fact near any massive gravitational body - so why not near a dense early universe?

I do not understand this - sorry please excuse my ignorance
But in its own frame, time is not 'dilated' in a dense object ... on the surface of a white dwarf or neutron star, or in orbit just above the event horizon of a (supermassive, so tidal effects can be ignored) black hole, all clocks tick the same (as comparable clocks - compare those on a neutron star with others on the same neutron star, for example). Similarly, inside the universe, there is only itself to compare (if there were an 'outside', then 'universe' would need re-defining).

Further, this 'time dilation' comes with GR; so wherever GR doesn't apply (e.g. the first Planck second, a 'different' universe, 'outside' the universe), you can have no basis for assuming time dilation applies too - 'time' might be fractal, or multi-dimensional, or even meaningless.

400poundgorilla
2005-Mar-16, 08:59 PM
Mild Mannered,

Lastly maybe I'm wrong but if the fabric of the Universe is getting overall less dense then Time is speedding up! (Near Black Holes it is slow because of extreme density)

I'm not sure why, but I'm thinking that it would be just the opposite. Piersdad seemed to have the same thought;

a foot note here
I read that when some scientists were reviewing all the measurements of the speed of light from a 100 years ago their methoids were accurate enough to stand up to present day measurements.
and they noticed that the average measurement then was slightly faster then than it is now.
the assumption then is the perhaps time itself is slowing down as the universe expands
Time is all relative to the observer though.

What about Gravity and the warping of the space time continum and this weird frame-dragging effect as predicted by AE? Does the spinning of mass also affect time? What about expansion?

Have we gotten off topic? Maybe I had better change threads for a while. :huh:

Mild mannered
2005-Mar-18, 01:09 PM
Have we gotten off topic?

Sorry I didn't realise - jumped in halfway through the thread and just got caught up.

I have a comment on the issue with time we were discussing - if this needs to be moved then I understand - I do not know how to myself.



But how could you ever tell?

SR has been so successful that length are now defined in terms of c (SI definition), and measurements of time are now (or soon will be) so accurate that comparisons between different locations will be all but impossible.

Several sets of observations have been made into whether the fine structure constant has changed over cosmological time (e.g. the last several billion years on Earth; the last 10 billions years or so in the universe) ... the best work is consistent with alpha being constant (to parts per million or billion per annum) ... which implies many fundamental constants are just that (at least since the era of the CMBR).

This was in response to my suggesting a change in the rate of time between now and the early Universe.

Perhaps dilated was an incorrect term - compacted maybe? If I see a clock near to a blackhole it appears to be almost stationary yet to the person holding that clock it is ticking away merrily at the same speed -I agree it is relative - nevertheless our clocks are ticking at different rates - he the person holding that clock is essentially traveling into the future. If he were to suddenly be released from the black hole and join me I would have aged and he would not etc.

I was thinking about this in relation to all energy. Is the energy that leaks from black holes in Hawking radiation recycled energy from the past? Is it's internal time clock set differently to mine - as if energy from the past had travelled to the future? (a window on the past that doesn't depend on distance like light fro mother galaxies) Perhaps it is a meaningless question afterall but I just wondered.

On the rate of time - I have always thought of Universal time as being like a computer program - when the [matter in the] Universe is very dense (like a black hole) information rates are slow just like my computer when it is trying to process too much information at once. It speeds up as the information gets less dense.


... the best work is consistent with alpha being constant (to parts per million or billion per annum) ... which implies many fundamental constants are just that (at least since the era of the CMBR).

Nereid: What about this quote from the New Scientist article you posted a link to?

"IN 1997 astronomer John Webb and his team at the University of New South Wales in Sydney analysed the light reaching Earth from distant quasars. On its 12-billion-year journey, the light had passed through interstellar clouds of metals such as iron, nickel and chromium, and the researchers found these atoms had absorbed some of the photons of quasar light - but not the ones they were expecting.

If the observations are correct, the only vaguely reasonable explanation is that a constant of physics called the fine structure constant, or alpha, had a different value at the time the light passed through the clouds."

Mild

Mild mannered
2005-Mar-18, 01:24 PM
Originally posted by antoniseb+Jan 29 2005, 05:58 AM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (antoniseb @ Jan 29 2005, 05:58 AM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-claycravens@Jan 29 2005, 05:37 AM
Does the Equivalence Principle apply to the acceleration in expansion of the universe?
That&#39;s a good question. I&#39;d start by assuming no. What would you measure it against. No one part of the universe would feel the acceleration. If it is yes, allow for other effects to need to be accounted for on that scale. Also, for any one place, the acceleration of expansion is *very* slow, and relativity may not be an important consideration. [/b][/quote]
Back on topic&#33;

No one part of the universe would feel the acceleration.

Are we 100% sure on this? I have no idea.

What about the pioneer probe mystery? Could it&#39;s unexplained acceleration be evidence that the part of the universe it is moving trough is expanding faster at that point - would that effect somehting so large? Is it being effected by the same force that is accelerating the expansion of the Universe?

Nereid
2005-Mar-18, 02:14 PM
Originally posted by Mild mannered
Nereid: What about this quote from the New Scientist article you posted a link to?

"IN 1997 astronomer John Webb and his team at the University of New South Wales in Sydney analysed the light reaching Earth from distant quasars. On its 12-billion-year journey, the light had passed through interstellar clouds of metals such as iron, nickel and chromium, and the researchers found these atoms had absorbed some of the photons of quasar light - but not the ones they were expecting.

If the observations are correct, the only vaguely reasonable explanation is that a constant of physics called the fine structure constant, or alpha, had a different value at the time the light passed through the clouds."
Yes, I&#39;m aware of this team&#39;s work.

However, there are several other papers on the constancy of alpha, from other researchers (some much more recent), using different techniques. Webb et al&#39;s result is anomalous. Here&#39;s an excellent 2003 paper by Bahcall (http://arxiv.org/abs/astro-ph/0301507) on this topic; among other things, he shows why the Webb team&#39;s result is problematic.

Nereid
2005-Mar-18, 02:18 PM
No one part of the universe would feel the acceleration.
Are we 100% sure on this? I have no idea.

What about the pioneer probe mystery? Could it&#39;s unexplained acceleration be evidence that the part of the universe it is moving trough is expanding faster at that point - would that effect somehting so large? Is it being effected by the same force that is accelerating the expansion of the Universe?
You can suss this out for yourself mild; what is the value of the anomalous acceleration observed in Pioneer? How does this value compare with that determined from analysing light curves from distant supernovae?

Mild mannered
2005-Mar-18, 02:54 PM
Originally posted by Nereid@Mar 18 2005, 02:18 PM
You can suss this out for yourself mild; what is the value of the anomalous acceleration observed in Pioneer? How does this value compare with that determined from analysing light curves from distant supernovae?
Sure

There is of course a huge difference - that&#39;s not quite what I meant - just that we don&#39;t understand either mechanism - acceleration of the expansion of the Universe and unexplained acceleration of Pioneer craft - I was just wondering if there was a correlation in these cases

Probably not - I agree - as the difference is so huge

Thanks for your kind responses

Mild