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Author Topic: What other evidence do we have of the expanding universe?  (Read 22502 times)

Charlie Ross

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Charlie Ross  asked the Naked Scientists:
   
Thanks for the podcasts, they're really really great!

I've got an astronomy question which has been bugging me for a while.  I'm sure I am missing details and am wrong.  I was hoping you could explain and make me less wrong.  :-)

As far as I know, the current best theory is that the universe is expanding, and the rate of expansion is increasing.
And if you ask how we know it, astronomers point to the red-shift of the light from distant stars, and how it gets more and more red-shifted the farther out the star is in a pattern that is consistent with an accelerating expansion.

(Am I close?).  But my question is:  is this the only way we know that the rate of expansion is increasing?

The reason I ask, is that I have not heard a good explanation for a mechanism that would cause that sort of accelerating expansion.
Its easy to accept that the universe is expanding, but the idea that the rate of expansion is increasing is harder.

So, how do we know that there is not some other phenominon at work that makes "nice normal explainable expansion" look like "accelerating expansion"?

I've been pondering this and have a few alternatives, and I am wondering how scientists rule them (or some combination of them) out.
I'm sure I am not the first to suggest such things, but I can't seem to find information about why these ideas were rejected.

From my college physics classes I remember there being some president for time-space being somewhat malleable.
For example, is it possible that time is accelerating?  I.e. time was moving more slowly in the past compared to today?
If time were accelerating, when we looked at very distant objects we would effectively be seeing light that started out its journey in a slower time-frame than the one it arrives in.   It would be like looking at objects running in slow motion... and we should see some sort of red-shifting from that, right?  (In addition to any red shift from motion)  How do we know that this isn't the case?  (I realize we would need to come up with an explanation for time speeding up... but that doesn't seem any messier than explaining why expansion is accelerating.)

Another possibility might be red-shifting due to the light starting in an area with stronger gravity, and getting to us now in an area with comparatively weak gravity.  In the past, the entire universe was overall more dense, so had more gravity, and now it is less dense so we have less.  Doesn't gravity cause red-shifting like this?  Wouldn't this also cause further objects to be more shifted?

I'm sure these ideas are not new... I just don't know what makes astronomers think they are wrong.
It seems to me that one, or the other, or some combination of both, or some combination of them and other ideas might fit observations.

I suspect I am very wrong here in several ways, and want to be less wrong.

Help me Naked Astronomers!  You're my only hope!

Charlie

What do you think?
« Last Edit: 05/06/2011 17:30:02 by _system »


 

Offline Atomic-S

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What other evidence do we have of the expanding universe?
« Reply #1 on: 06/06/2011 05:33:29 »
I am not sure anyone knows the answers to these questions.
 

Offline imatfaal

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What other evidence do we have of the expanding universe?
« Reply #2 on: 06/06/2011 12:00:46 »
Per Atomic - there are a lot of unknowns.  On the observation side - one can never rule out the action of little pink fairies, but we tend to try and go for the simplest explanation and work upwards.  The least complicated (and this is only in relative terms) that we can come up with to explain observations is that universe is expanding and the rate of expansion is increasing.  We could, almost certainly, take individual stars and redshifts and explain them by changed behaviour of light, time, and/or gravity.  the problem is getting a theory like this to be universally applicable - the cmbr is almost isotropic so any solution has to apply everywhere.
 

Offline Geezer

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What other evidence do we have of the expanding universe?
« Reply #3 on: 06/06/2011 18:39:44 »
I had, though I say it myself, a brilliant bit of insight into this the other day.

It seems to me that the acceleration is necessary because it's the only way it could work! I'm not sure exactly how to explain it mathematically, but if all space is expanding (and presumably it is) then things become very nonlinear at great distances.

No doubt my learned colleagues will accuse me of over indulging in the tonic wine, but I'm pretty sure I'm right about this (er, well, it seems like a good guess anyway.)
 

Offline CliffordK

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What other evidence do we have of the expanding universe?
« Reply #4 on: 06/06/2011 20:24:28 »
For example, is it possible that time is accelerating?  I.e. time was moving more slowly in the past compared to today?
Anybody that has reached their middle ages will tell you this is definitely true.  Time went much slower when they were children than when they became adults.

But...  in a real sense, in a fixed reference frame, it would be difficult to envision accelerating time.  However, the interaction of other bodies with that reference frame can certainly change.

I haven't read any of the primary sources, but I would think that an acceleration of the expansion of space would be the weakest part of the argument. 

I presume there are multiple things aspects that can be correlated with redshift and distance.  So, for example, size would tend to decrease with distance, and the theories would also indicate things like metalicity would also decrease with extreme distance.

One of the points that I've made earlier is that our most distant views of our universe extends to over 10 billion light years.  Many of the stars we're seeing will likely have died since the time when the light was originally generated, and any conclusions of what those stars are doing today would be pure speculation.  The more distant portions of the universe could be collapsing today, and we wouldn't know it until long after our own sun burns out billions of years in the future.
 

Offline yor_on

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What other evidence do we have of the expanding universe?
« Reply #5 on: 07/06/2011 02:24:06 »
There are a lot of evidence for both a inflation and a expansion. Without it not only our red and blue shift will fall but also the way we expect our universe to have built itself up from that primeval plasma. It's a story that started a long time ago, involving nuclear physics, how matter came to be, why we started to look for the cosmic background radiation, etc etc. and it's the best theory we have for the moment.

It may seem weird but we need it :)
 

Offline Geezer

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What other evidence do we have of the expanding universe?
« Reply #6 on: 07/06/2011 07:40:15 »

Many of the stars we're seeing will likely have died since the time when the light was originally generated, and any conclusions of what those stars are doing today would be pure speculation. 


The current state of those stars doesn't really matter. The light that they emitted has been frequency shifted when we observe it, and the shift is consistent with acceleration at greater distances.

If we accept that our observations are not somehow flawed, the data clearly indicate that distant objects were accelerating from us. Unless we think there is something "special" about our vicinity in space, it's hardly surprising that we observe acceleration. There would have to be something really weird going on if objects were receding without acceleration.
 

Offline MikeS

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What other evidence do we have of the expanding universe?
« Reply #7 on: 07/06/2011 09:33:00 »
No doubt someone will correct me if I am wrong but I believe the age of the universe has been estimated by observing early quasars, or galaxies containing quasars.  The problem with this being, it has been observed that some quasars that appear to be connected to galaxies are magnitudes of distance further away than the associated galaxy according to their red shift.  This being the case, quasars should not be relied upon as true indicators for red shift.  It follows from this that the universe may be much younger, smaller and accelerating a lot more slowly than is generally thought. 

I could add more but then it would be thought of as new physics. 

I should perhaps just add this.  When observing a massive object like a galaxy containing a quasar, has gravitational time dilation (red shift at source) been taken into account, I seriously doubt it.
 

Offline Geezer

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What other evidence do we have of the expanding universe?
« Reply #8 on: 07/06/2011 18:36:33 »
I think it's only the "brightness" of quasars that is used to estimate distance. The recession rate of a galaxy is estimated from the galaxy's overall spectrum.

If anomalies in frequency observations of quasars indicate that our observations are inconsistent it would only mean that the correlation between galaxy distance and speed was less strong. The speeds of the galaxies would still be the same.
 

Offline PhysBang

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What other evidence do we have of the expanding universe?
« Reply #9 on: 09/06/2011 13:22:47 »
Quote from: Charlie Ross  link=topic=39707.msg358106#msg358106 date=1307291402
But my question is:  is this the only way we know that the rate of expansion is increasing?
Not quite. Because we can look at the effect that the expansion has on the overall geometry of the universe between here and the point where the background radiation was emitted. This overall geometry is influenced by the overall expansion. Thus when we are able to figure out the size of a feature in the background radiation and compare it to how we see that size here, we can see the overall effect of expansion, more or less. Then we combine this with the known features of expansion (the current rate and how much the mass in the universe could possibly slow down expansion) and we get a measurement of any acceleration that must have happened to the expansion.

This background radiation evidence is the stuff that the cosmologists themselves tend to find really convincing, moreso than the supernovae observations.
Quote
So, how do we know that there is not some other phenominon at work that makes "nice normal explainable expansion" look like "accelerating expansion"?
Part of the reason is that the systematic errors that might explain away some observations don't play a role in other observations. For example, while dust might interfere with our observations of brightness and redshift, it shouldn't play a role in our observations of the background radiation. Thus we can more or less rule out these other explanations.
Quote
I've been pondering this and have a few alternatives, and I am wondering how scientists rule them (or some combination of them) out.
I'm sure I am not the first to suggest such things, but I can't seem to find information about why these ideas were rejected.
You might want to check out Robert Kirshner's book, The Extravagant Universe. He was part of a team that found the acceleration initially and in the book he goes over the project in a very accessible manner. In the revised edition he talks about how using the background radiation observations was very convincing.
Quote
From my college physics classes I remember there being some president for time-space being somewhat malleable.
For example, is it possible that time is accelerating?  I.e. time was moving more slowly in the past compared to today?
Not quite, since the expansion has changed relative to ordinary physical processes. However, the expansion itself is a feature of malleble spacetime. We can actually chart the expansion through the time delay it introduces into the processes that we observe.
Quote
Another possibility might be red-shifting due to the light starting in an area with stronger gravity, and getting to us now in an area with comparatively weak gravity.  In the past, the entire universe was overall more dense, so had more gravity, and now it is less dense so we have less.  Doesn't gravity cause red-shifting like this?  Wouldn't this also cause further objects to be more shifted?
The problem with this idea is that on smaller (intergalactic!) scales we are considering light moving from a dense area into an equally dense area. Taking into account to overall thinning out of the universe over time is what produces the standard redshift of cosmology.
 

Offline yor_on

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What other evidence do we have of the expanding universe?
« Reply #10 on: 15/06/2011 16:07:18 »
There's one more thing as I see it.

Any red and blueshift is a result of a relation. The expansion is unique in that its interaction leaves the light 'stretched out' for 'eternity' and us to observe. A gravitational field may bend light and make it be blue shifted, if you are on the planet 'bending it' for example, or inside that gravitational field. But as fast as that light have passed the 'gravitational field' it will lose whatever 'blue shift' you observed. That it is so is because we have found that, treating it as photons for this, light quanta have one 'energy', even though the degree of energy in a photon may differ it is constant from source to sink. And all added, or subtracted, 'energy' can only come to be from interactions with something else. Not so with the expansion, the idea there is that points of 'new space' comes to be between galaxies filling it in, sort of :)

And assuming that light propagates even when not observed and then defining it as a wave we now will find as the 'metric' of space elongates so will that wave elongate. And a wave that you 'stretch out' loses 'energy', and becomes of a lower frequency. That means, becomes red shifted.

So there is a difference.
 

Offline yor_on

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What other evidence do we have of the expanding universe?
« Reply #11 on: 29/06/2011 05:01:58 »
And then, if we now accept this. Gravity defines both lights 'frequency' as in a wave and 'energy'. And the truly big difference is that it defines it globally. To see why that one is surprising we have to look at 'locality'. If you define SpaceTime locally solely you will get one speed only for light, making it into the perfect beat holder for 'times arrow', and that will fit the arrow as hand in glove. Using that definition we can now look at SpaceTime defining all comparisons between frames of reference (you versus the universe) as mediated by that beat holder, except the expansion. If this is correct then gravity becomes what keeps us, including light, together. Otherwise I find it hard to see how it would be able to define a whole SpaceTime, as it actually does defining the redshift?

All building on light being what enable me to compare 'frames of reference'.
 

Offline Mr. Data

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What other evidence do we have of the expanding universe?
« Reply #12 on: 29/06/2011 05:06:44 »
Charlie Ross  asked the Naked Scientists:
   
Thanks for the podcasts, they're really really great!

I've got an astronomy question which has been bugging me for a while.  I'm sure I am missing details and am wrong.  I was hoping you could explain and make me less wrong.  :-)

As far as I know, the current best theory is that the universe is expanding, and the rate of expansion is increasing.
And if you ask how we know it, astronomers point to the red-shift of the light from distant stars, and how it gets more and more red-shifted the farther out the star is in a pattern that is consistent with an accelerating expansion.

(Am I close?).  But my question is:  is this the only way we know that the rate of expansion is increasing?

The reason I ask, is that I have not heard a good explanation for a mechanism that would cause that sort of accelerating expansion.
Its easy to accept that the universe is expanding, but the idea that the rate of expansion is increasing is harder.

So, how do we know that there is not some other phenominon at work that makes "nice normal explainable expansion" look like "accelerating expansion"?

I've been pondering this and have a few alternatives, and I am wondering how scientists rule them (or some combination of them) out.
I'm sure I am not the first to suggest such things, but I can't seem to find information about why these ideas were rejected.

From my college physics classes I remember there being some president for time-space being somewhat malleable.
For example, is it possible that time is accelerating?  I.e. time was moving more slowly in the past compared to today?
If time were accelerating, when we looked at very distant objects we would effectively be seeing light that started out its journey in a slower time-frame than the one it arrives in.   It would be like looking at objects running in slow motion... and we should see some sort of red-shifting from that, right?  (In addition to any red shift from motion)  How do we know that this isn't the case?  (I realize we would need to come up with an explanation for time speeding up... but that doesn't seem any messier than explaining why expansion is accelerating.)

Another possibility might be red-shifting due to the light starting in an area with stronger gravity, and getting to us now in an area with comparatively weak gravity.  In the past, the entire universe was overall more dense, so had more gravity, and now it is less dense so we have less.  Doesn't gravity cause red-shifting like this?  Wouldn't this also cause further objects to be more shifted?

I'm sure these ideas are not new... I just don't know what makes astronomers think they are wrong.
It seems to me that one, or the other, or some combination of both, or some combination of them and other ideas might fit observations.

I suspect I am very wrong here in several ways, and want to be less wrong.

Help me Naked Astronomers!  You're my only hope!

Charlie

What do you think?

Time is moving more slower in the past than it is today? Even though there are solutions to physics which state that the last few seconds of a big crunch will seem like an eternity, this requires someone is there to observe this fact. If time moved slower in the past, what is time moving relative to?
 

Offline Mr. Data

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What other evidence do we have of the expanding universe?
« Reply #13 on: 29/06/2011 05:09:04 »
In other words, time does not move. It has no flow. Time does not even have a physical substance. It seems the perception of time is all we have, created by the Suprachiasmatic Nucleus - the physical gene responsible for our perception of time. Hence why the psyhological arrow is the true and only kind of arrow in quantum physics. But no... time does not flow, has no movement relative to anything else. It is only relative to an experiencing observer.
 

Offline Mr. Data

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What other evidence do we have of the expanding universe?
« Reply #14 on: 29/06/2011 05:10:52 »
Second Community Prizes


The Flow of Time*
By George F. R. Ellis


Essay Abstract
Current theoretical physics suggests the flow of time is an illusion: the entire universe just is, with no special meaning attached to the present time. This paper points out that this view, in essence represented by usual space-time diagrams, is based on time-reversible microphysical laws, which fail to capture essential features of the time-irreversible nature of decoherence and the quantum measurement process, as well as macro-physical behaviour and the development of emergent complex systems, including life, which exist in the real universe. When these are taken into account, the unchanging block universe view of spacetime is best replaced by an evolving block universe which extends as time evolves, with the potential of the future continually becoming the certainty of the past; spacetime itself evolves, as do the entities within it. However this time evolution is not related to any preferred surfaces in spacetime; rather it is associated with the evolution of proper time along families of world lines. The default state of fundamental physics should not be taken to be a time irreversible evolution of physical states: it is an ongoing irreversible development of time itself.

Author Bio
George Ellis is Professor Emeritus of applied mathematics at the University of Cape Town. He has written or co-authored many books and papers on relativity theory and cosmology, including On the Large Scale Structure of Space Time with Stephen Hawking.

download essay • discuss essay back to top


extracted from

http://fqxi.org/community/essay/winners/2008.1

A lot of nice reading in there if anyone wants to understand how time enters physics and GR.
 

Offline Airthumbs

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What other evidence do we have of the expanding universe?
« Reply #15 on: 29/06/2011 17:39:24 »
Here is a scary thought....... because light takes so long to get here from the edges of our expanding Universe how would we know if the Universe was rebounding and on its way back to a big crunch? 
 

Offline yor_on

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What other evidence do we have of the expanding universe?
« Reply #16 on: 29/06/2011 17:55:24 »
Time is very much a fact. The arrow is not for us to play with. If it was we could assume that we already is being manipulated by 'time travelers', assuming that the macroscopic arrow we have allowed it, which I truly doubt. Then again, I assume that we all are isolated islands, don't I :) joined by perception and our senses informing us that we all are here together. That one is about light (radiation) of course, it's what you use to define other frames, nothing else. And the universe becomes weird :) doesn't it?

But the arrow exist, and its beat is light, at least as I think of it, going out from what I call 'locality'. Which always will be a equivalence to 'black room scenarios', such as Einstein used to define uniform, and accelerating, motion. Well accelerating motion primary, but you can as easily use it for uniform. It goes back to what your definitions of 'reality' is. Do you trust your senses? Do you expect the 'thingies' you see to define reality as it really is? What about a Lorentz contraction? A 'time dilation'?

Easiest way to define it is from 'locality'. That as we all must have a unique relation to all other frames of reference, as I see it (and Einstein too). And it surprises me that he didn't went all the way with it, my guess is that all that rigorous math defining his ideas took over, it's also flattering to find that you suddenly is in the 'lime light' surrounded by interesting and highly intelligent people. We're all human, and we lose sight at times. But relativity isn't weird, it's implications though is seriously 'twisted' :) But he*, we're here for a short time only so who have the right to tell you that you can't imagine?
 

Offline yor_on

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What other evidence do we have of the expanding universe?
« Reply #17 on: 29/06/2011 18:09:56 »
So let us assume that you make a time machine, from my scenario of you being an island in a sea of light, or maybe 'gravity' is more correct? That is, if we assume 'action and reaction' and 'inflation/expansion' defining instants in a linear procession somehow.

Sure, you goes 'back', but the ones around you doesn't. You can't 'time travel' in my definition. The only way you can imagine it is if you found a way to not only influence your own 'locality', but also all others. And I don't see how you could do that? But that opens for questioning how we then can 'time travel' forward in 'time', doesn't it? That one I will need to find a explanation for. You might assume what we already see of course, a arrow pointing in only one direction, towards a 'future'. Or you could assume that there is a reversibility possible, defining it as such as when you do use that 'time machine' the universe you 'see' is 'forced' to present you with what you then would expect to see? But that one assumes that you by manipulate a finite amount of energy can force a whole universe's energy to adapt to you? That one is seriously twisted, isn't it?

As one of the things I do think is true is that there are two 'states'. One is uniform motion, not expending 'energy', the other is accelerations, expending 'energy'. Ah well, I don't know really. A cool link btw, I will read it :)
« Last Edit: 29/06/2011 18:17:59 by yor_on »
 

Offline yor_on

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What other evidence do we have of the expanding universe?
« Reply #18 on: 29/06/2011 18:36:01 »
Well, assuming locality we do have a perfect clock? All of us do, and it's called lights invariant speed in a vacuum. Most confusion I get is from those thinking in terms of conceptuality, as in comparing frames of reference. If you define the universe such you will have a complicated reality. If you do as I you will have a twisted one, but simpler.

From my definition, you have one beat, only one and that is a constant, just as Einstein defined it. But the beat is 'local' and must be understood to be so, if you fail that one you won't be able to define SpaceTime. It's like a puzzle you try to lay, the normal way is to look at all the pieces, and then try to fit them. But in this case the only piece you need, is to understand one of them, and from there by using radiation, gravitation, and 'beats' define how a common SpaceTime will fall in place, looking 'out' from that definition. And even though it makes sense to me, it does not take hold of why we then would 'exist', to be seen by each other, so it's nowhere near defining what reality really, really, is :)

But it makes sense to me, in a seriously twisted way of course.
 

Offline Mr. Data

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What other evidence do we have of the expanding universe?
« Reply #19 on: 29/06/2011 18:37:08 »
Time is very much a fact. The arrow is not for us to play with. If it was we could assume that we already is being manipulated by 'time travelers', assuming that the macroscopic arrow we have allowed it, which I truly doubt. Then again, I assume that we all are isolated islands, don't I :) joined by perception and our senses informing us that we all are here together. That one is about light (radiation) of course, it's what you use to define other frames, nothing else. And the universe becomes weird :) doesn't it?

But the arrow exist, and its beat is light, at least as I think of it, going out from what I call 'locality'. Which always will be a equivalence to 'black room scenarios', such as Einstein used to define uniform, and accelerating, motion. Well accelerating motion primary, but you can as easily use it for uniform. It goes back to what your definitions of 'reality' is. Do you trust your senses? Do you expect the 'thingies' you see to define reality as it really is? What about a Lorentz contraction? A 'time dilation'?

Easiest way to define it is from 'locality'. That as we all must have a unique relation to all other frames of reference, as I see it (and Einstein too). And it surprises me that he didn't went all the way with it, my guess is that all that rigorous math defining his ideas took over, it's also flattering to find that you suddenly is in the 'lime light' surrounded by interesting and highly intelligent people. We're all human, and we lose sight at times. But relativity isn't weird, it's implications though is seriously 'twisted' :) But he*, we're here for a short time only so who have the right to tell you that you can't imagine?

There is no arrow, unless you are referring to a psychological arrow.
 

Offline yor_on

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What other evidence do we have of the expanding universe?
« Reply #20 on: 29/06/2011 18:54:21 »
That's where we differ, I see a arrow macroscopically, and it has a beat, which I presume to be lights. That as it has only one beat locally, and just as your experience of 'time' never changes. Both of those are facts, your lifespan is the same wherever you are, that you find the relations you have relative the universe to change is about a relation, not about a 'common time'. Although every object you see will have a defined unique relation relative you, and another relative any other object, which then will be different than yours to that same object, all of this can be followed to one simple constant, light. And the beat of light is constant locally, as your time. And there is a direction.
 

Offline Mr. Data

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What other evidence do we have of the expanding universe?
« Reply #21 on: 29/06/2011 18:59:52 »
That's where we differ, I see a arrow macroscopically, and it has a beat, which I presume to be lights. That as it has only one beat locally, and just as your experience of 'time' never changes. Both of those are facts, your lifespan is the same wherever you are, that you find the relations you have relative the universe to change is about a relation, not about a 'common time'. Although every object you see will have a defined unique relation relative you, and another relative any other object, which then will be different than yours to that same object, all of this can be followed to one simple constant, light. And the beat of light is constant locally, as your time. And there is a direction.

There is no macroscopic body in a full quantum theory. Quantum theory deals with the high energy physics, while the low energy physics is left to Newtonian Dynamics, and the added information from General Relativity which describes bodies at large. There is no absolution yet with ''sizes'' in physics which makes sense beyond high energy physics.
 

Offline yor_on

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What other evidence do we have of the expanding universe?
« Reply #22 on: 29/06/2011 19:01:38 »
You can see it two ways. Either you define that local beat as a universal constant (ground state) but then remembering that you have to go out from locality to see it. Or you you compare in which case you will find it questionable, to then fall into defining all sort of things to explain why your comparison's differ, from variable constants to the beat being an illusion. Time as such have a direction as any experiment anyone ever done proves. We all do them under the arrow, drawing our conclusions, presuming a causality that holds true. Without that presumption no definitions are possible, even those presuming 'no time' at all.
 

Offline yor_on

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What other evidence do we have of the expanding universe?
« Reply #23 on: 29/06/2011 19:05:04 »
As for discussing it from various definitions of reality? I discuss time here, and as I pointed out, all experiments presumes a causality, from where you draw your conclusions. That causality is what I call our arrow of time macroscopically. That we can find chains that you can reverse conceptually in QM does not change this.
 

Offline Mr. Data

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What other evidence do we have of the expanding universe?
« Reply #24 on: 29/06/2011 19:09:26 »
You don't understand General Relativity to make the statements you have, in comparison with Quantum Mechanics.
 

The Naked Scientists Forum

What other evidence do we have of the expanding universe?
« Reply #24 on: 29/06/2011 19:09:26 »

 

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