Science Questions

What other evidence do we have of the expanding universe?

Fri, 24th Jun 2011

Listen Now    Download as mp3 from the show Star Death, STEREO & South Africa’s SKA bid

Question

Charlie Ross asked:

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

Multimedia

Subscribe Free

Related Content

Comments

Make a comment

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? Charlie Ross , Sun, 5th Jun 2011

I am not sure anyone knows the answers to these questions. Atomic-S, Mon, 6th Jun 2011

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. imatfaal, Mon, 6th Jun 2011

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.) Geezer, Mon, 6th Jun 2011


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. CliffordK, Mon, 6th Jun 2011

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 :) yor_on, Tue, 7th Jun 2011



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. Geezer, Tue, 7th Jun 2011

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. MikeS, Tue, 7th Jun 2011

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. Geezer, Tue, 7th Jun 2011


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.

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.

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.

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.

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. PhysBang, Thu, 9th Jun 2011

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. yor_on, Wed, 15th Jun 2011

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'. yor_on, Wed, 29th Jun 2011



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? Mr. Data, Wed, 29th Jun 2011

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. Mr. Data, Wed, 29th Jun 2011

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. Mr. Data, Wed, 29th Jun 2011

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?  Aaron_Thomas, Wed, 29th Jun 2011

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? yor_on, Wed, 29th Jun 2011

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 :) yor_on, Wed, 29th Jun 2011

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. yor_on, Wed, 29th Jun 2011



There is no arrow, unless you are referring to a psychological arrow. Mr. Data, Wed, 29th Jun 2011

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. yor_on, Wed, 29th Jun 2011



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. Mr. Data, Wed, 29th Jun 2011

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. yor_on, Wed, 29th Jun 2011

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. yor_on, Wed, 29th Jun 2011

You don't understand General Relativity to make the statements you have, in comparison with Quantum Mechanics. Mr. Data, Wed, 29th Jun 2011

Ah, I stand corrected :)

So let us assume that we have a different opinion then, shall we? yor_on, Wed, 29th Jun 2011



It is only worthy to understand there are different points, if the one who holds the most knowledge on the subject can admirally stand and make their points in the name of science. I can honestly, nit and pick at many things people have said. But it has no consequence unless I show quantitative evidence. Mr. Data, Wed, 29th Jun 2011

:) yor_on, Wed, 29th Jun 2011

I can show evidence though... can you? Mr. Data, Wed, 29th Jun 2011

For what? yor_on, Wed, 29th Jun 2011



What do you think for? Mr. Data, Wed, 29th Jun 2011

Are you questioning lights speed in a vacuum? Or that your lifespan is of one measure, no matter where you are? Both of those will, measured locally, be 'invariant' as far as I know?

That's where I see a equivalence between 'times arrow' and lights 'beat'.

When it comes to Lorentz transformations and 'time dilations' the best example I know of is those atomic clocks that starts synchronized on a table, then you lift one to the floor, watching them becoming desynchronized. There are your 'frames of reference', as well as 'time dilations'. It's always a relation between frames of reference, and both clocks locally measure the same invariant speed 'c', just as you watching them.

Or, can you prove it otherwise? yor_on, Wed, 29th Jun 2011

What? Mr. Data, Wed, 29th Jun 2011

Well Mr. Data, I think that was my question?
What exactly are you disputing? yor_on, Wed, 29th Jun 2011



If you introduce a cascade of new things, perhaps you could elaborate on this tenebrous situation. Mr. Data, Wed, 29th Jun 2011

Sorry Mr. Data I just gave you some few definitions. They are actually quite simple, extrapolating from them you find all sort of 'twisted' things becoming true. But as I said, it's about where your definitions lay. Mine is about what I define as 'locality' meaning measurements you do from, and in, your own 'frame of reference' (loosely speaking here). Also I use what Einstein referred to as 'black room scenarios' to define what I consider 'reality'.

It's more of a presumption naturally. None of us can say that one way of defining anything will lead us to the way SpaceTime might use. I assume that 'simplifying it' will lead me in the right direction, and so I use 'locality' as from where I look at things. And from there I draw my conclusions. On the other hand :) I do not state it as a theory, to me it's just a first hypothesis, meaning that I'm willing to listen to any understandable disputation about my 'basics'. That's also why I wondered where you found my conclusions lacking. yor_on, Wed, 29th Jun 2011



Let us just say, I would not say what you say. The conclusions lacked with the site which was given (please let this be the same page) - I remember reading a link which contained a fabrication in the first sentance.

Mr. Data, Wed, 29th Jun 2011

In fact, if there is no link in this page, I just need to have a quick look at your physics as well:

''I see a arrow macroscopically, and it has a beat, which I presume to be lights.''

And know it's bogus. Mr. Data, Wed, 29th Jun 2011

Good, then you don't agree on that light locally always is of the same invariant speed?
Or is that you define a lifespan from conceptuality, comparing it to (other) frames of reference? yor_on, Wed, 29th Jun 2011



No. There is no absolute time reference.




End of. Mr. Data, Wed, 29th Jun 2011

The last simply means that you define 'age' not from your own frame of reference, but from what you see the universe show you (time dilations). That's also what I used the atomic clocks to show. yor_on, Wed, 29th Jun 2011

There does exist an asymptotic time frame. That is the present moment, but that requires observer-physics. How attuned are you to decoherence physics, or even weak measurements? Mr. Data, Wed, 29th Jun 2011

Well, that's your definition then. And that's one you will have to prove, preferably simple enough, that we all can see how you mean. yor_on, Wed, 29th Jun 2011



Age can only be defined in a universe where matter and energy acts as clocks. If there are contraints on the subject at hand, our cananonical equations are basically solutions to timeless physics. General Relativity predicts unfortunately the same thing under tranformations called diffeomorphism contraints. Mr. Data, Wed, 29th Jun 2011



I'll explain my topics if you want to learn? Mr. Data, Wed, 29th Jun 2011

There are some restrictions. If it's a mainstream topic we can discuss it here, if it deviates into a theory without, or very little, mainstream support we're expected to use 'New theories' for it. Think it over and decide where you want to start your topic, I'm always willing to listen :) yor_on, Wed, 29th Jun 2011



There is plenty validation as I have paper support of several prominent scientists. So this now a matter of references:

http://www.fqxi.org/data/essay-contest-files/Ellis_Fqxi_essay_contest__E.pdf

http://www.fqxi.org/community/forum/topic/360 Mr. Data, Wed, 29th Jun 2011

There are all kinds of hypothesis's out in cyberspace Mr. Data. To make it a fact you will have to prove it experimentally. But I'm a little disappointed here. I expected you to be fluent enough to create and define what you thought correct yourself?

As you seemed so sure on your idea(s)? yor_on, Wed, 29th Jun 2011

As for "where matter and energy acts as clocks."?

How?

As I think of it you have light as the clock, locally defining a beat. Put those 'locality's' together, then introduce 'relative motion' and mass (relative 'gravity') and you will find time dilations and Lorentz contractions. But I track it to lights 'invariant beat' myself. That it never change 'speed' locally.

Are you thinking 'matter waves' there?
==

To my understanding, 'energy' is a result/definition we use relative transformations. It is a 'product' of transformations, but not anything I can see or touch. Simply expressed, there is no way of lifting forward a 'ounce of energy' that I know of at least? When it comes to its 'carrier' though, we have light (radiation) as our foremost example, in that we define it (mainstream) as massless and intrinsically 'timeless', defined as of a constant energy as well as speed, changing energy foremost as a result of a relation relative a observer. And that's what made the expansion so remarkable to me, in that it assumes 'gravity' (as I define that as the metric of space for this) to be able to change it over a whole SpaceTime. But maybe I could see 'gravity' as just another 'frame of reference'? The same as you could define the universe as presenting you with one 'joined frame', relative your own?
==

In fact, I would prefer to define 'gravity' as just another 'frame of reference'. That makes photons 'energy' invariant, which keeps it a little simpler to me. But that doesn't change the 'fact' that if you, as me, define 'space' from 'gravity's metric', you now have introduced a seamless frame that, in contrast to radiation, does not break down into 'quanta'.

But then again, this is a preference of mine, that on some plane it will all be 'seamless'. And that has to do with the assumption of a graininess creating a SpaceTime. To me a graininess does not answer what the graininess 'exist in'. It assumes a background to me, and so it can be no final answer. One of the things I like Smolin for is because he tries to create a background independent definition of SpaceTime, from strings and loops. In it those loops create the 'roomtime', as well as the 'background', all as I understands it. It's them 'joining' that creates what we see, all of it. It's all a question of your preferences of course, but it makes it simpler to understand for me.
==

Although there is a possibility of questioning loops and strings too it depends on how you see them. Imagine a one dimensional 'string' for this. 'Reality' is defined by three dimensions, and then the arrow that 'ticks' for us naturally, or our 'linear causality' if you like. A one dimensional string may have a length, but as it has no width and no height, it becomes very alike a boson to me? I've seen some imagining it able to 'cut' matter, but how would it ever be able to do that? What would 'cut'? It's imaginary width, height? I don't know, do you?

All of this assume a linearity though, a procession of logical building blocks, ending with our SpaceTime, or continuing into something even more 'dimensional'? 1, 2, 4, 8 (SpaceTimes 'corners') 16, 32, 64 ~ (I don't know where to stop here:) yor_on, Wed, 29th Jun 2011



I am with the idea that reality is not the true perception (and these general conclusions where made from the soil of General Relativity), that the world we observe is a secondary phase, with a horizon of sentient information; but of course that would be speculatory.

Mr. Data, Wed, 29th Jun 2011

Well, I agree with you actually :) But to me it also depend on where one stand. "Reality is not the true perception" Sure, if you as I define it from locality, but we don't, do we? We define 'reality' conceptually, never noticing it. Everything we do assume that we 'share' the same reality, at the same time that 'frames of reference' elegantly prove (as the atomic clocks) that there are no two points in SpaceTime that we can expect to be the exact same, time/gravity and possibly also 'energy' seen.

But we define reality as we grow up, and we don't find each other 'untouchable' as far as I know, so from the perspective of us living and dying together, we definitely exist together. In some way it becomes a question of semantics, but also of your logic. yor_on, Wed, 29th Jun 2011

As I see it both gravity and entropy are the main arrows of time.  The passage of time is set by the speed of light.  Time is a fundamental artefact of the universe.

Going back to the original question
What other evidence do we have of the expanding universe?
The expanding universe theory seems to be little more than a hypothesis based almost wholly on the interpretation of the red-shift.  Both the red-shift and the CBR can be equally well explained by time being dilated in the past.  Type 1a supernova provide evidence that time actually was dilated in the past.  All other distance markers that I know of are short or relatively short range.
I am not suggesting that the universe is not expanding, it's just that there does not seem to be much hard evidence that it is. MikeS, Thu, 18th Aug 2011


It does seem like this if one doesn't read anything in cosmology or astronomy.

They most certainly cannot. If anyone was able to do this, it would be a very impressive scientific coup.

In order to explain what we see of redshift, we would need to explain why time dilation occurred at all in the past and why the degree of time dilation changed first in one direction and then in another direction over cosmological time. Time dilation alone does not explain why there is a background radiation and it certainly doesn't explain why the background radiation has the detailed features that it does.

Type Ia supernovae results show that there is time dilation that is what one expects to see from an expanding universe. If one does away with expansion and simply introduces some kind of time dilation field, then one must also explain the observed distribution of galaxies in the past. PhysBang, Thu, 18th Aug 2011


It does seem like this if one doesn't read anything in cosmology or astronomy.

They most certainly cannot. If anyone was able to do this, it would be a very impressive scientific coup.

In order to explain what we see of redshift, we would need to explain why time dilation occurred at all in the past and why the degree of time dilation changed first in one direction and then in another direction over cosmological time. Time dilation alone does not explain why there is a background radiation and it certainly doesn't explain why the background radiation has the detailed features that it does.

Type Ia supernovae results show that there is time dilation that is what one expects to see from an expanding universe. If one does away with expansion and simply introduces some kind of time dilation field, then one must also explain the observed distribution of galaxies in the past.


I have read all I can find on the internet, that is why I came to this conclusion.  If I have missed anything, perhaps you would be good enough to quote references.

Photons arriving on Earth from the distant past are considerably red-shifted.  That is there are less of them arriving per second than would normally be expected and their wavelength is stretched.  To the best of my knowledge there are two explanation for this.  The universe is expanding or time is contracting.  From our perspective both effects look exactly the same.  There is no way of differentiating between them.

To answer this in this thread would put me in trouble with the moderators.
Please see this link for answer
http://www.thenakedscientists.com/forum/index.php?topic=40685.msg365375#msg365375

The background radiation may well be as explained by the big-bang model but again the red shift of the CBR would look the same through expansion or time dilation in the past.  There is no reason why time dilation in the past would cause the CBR to look any different than it does.  A given amount of expansion or a given amount of time dilation in the past would look exactly the same.

This is not what one expects to see 'just' from an expanding universe as it contains evidence that clocks ran slower in the past.
http://www.newscientist.com/article/dn13792-cosmic-time-warp-revealed-in-slowmotion-supernovae.html

Quite obviously the universe must have expanded at some point or it would be one large blob.  This explains the distribution of galaxies.  The question is whether it is still expanding and the rate of expansion.  I believe the observed cosmological red-shift is a mixture of expansion and time dilation/contraction.  When we ask how old is the Universe?  Is this a meaningful question if the passage of time is variable?  It's like measuring length with a piece of elastic. MikeS, Fri, 19th Aug 2011


You could start here: http://www.astro.ucla.edu/~wright/cosmolog.htm

However, I'd recommend going to a library and reading a general book on astronomy from the last 10 years.

I don't know what "time contracting" is. I know that the expansion of the universe causes time dilation which we see marked effects of in distant objects. If one is just going to say that time dilation just happens, then one might as well say that unicorns are causing redshift.

If there is just some magical time dilation, there is no reason for their to be a background radiation. There is no reason for this background radiation to carry information about large scale structure. So many things fall apart if we simply assume magical time dilation.

Expansion causes time dilation. We can measure features of expansion in many different ways. We cannot measure features of your magical time dilation in other ways. Also, we need a magical reason to have the background radiation. PhysBang, Fri, 19th Aug 2011


You could start here: http://www.astro.ucla.edu/~wright/cosmolog.htm

However, I'd recommend going to a library and reading a general book on astronomy from the last 10 years.



I don't know what "time contracting" is. I know that the expansion of the universe causes time dilation which we see marked effects of in distant objects. If one is just going to say that time dilation just happens, then one might as well say that unicorns are causing redshift.

If there is just some magical time dilation, there is no reason for their to be a background radiation. There is no reason for this background radiation to carry information about large scale structure. So many things fall apart if we simply assume magical time dilation.

Expansion causes time dilation. We can measure features of expansion in many different ways. We cannot measure features of your magical time dilation in other ways. Also, we need a magical reason to have the background radiation.


All of your points above were covered in my last post.

I don't know what "time contracting" is.
Time contraction is the opposite of time dilation.  Mainstream sometimes uses the term time dilation for both dilation and contraction which is really confusing.

I know that the expansion of the universe causes time dilation
That's interesting, how does that work?  Something to do with your unicorns and magic perhaps?

which we see marked effects of in distant objects.
What marked effects?

If one is just going to say that time dilation just happens, then one might as well say that unicorns are causing redshift.
I answered that in my last post
http://www.thenakedscientists.com/forum/index.php?topic=40685.msg365375#msg365375


If there is just some magical time dilation, there is no reason for their to be a background radiation. There is no reason for this background radiation to carry information about large scale structure. So many things fall apart if we simply assume magical time dilation.
This was covered in my last post

Expansion causes time dilation.
No, it does not.  The 'effects' of expansion and or time dilation merely look the same from our reference frame.
Type 1a supernova show that time is contracted now, dilated in the past.  Clocks are now ticking faster not slower.

We can measure features of expansion in many different ways.
What ways, other than those I have already mentioned and explained, namely:-
red-shift, type 1a supernova, CBR, Olbers paradox and short to mid range cosmological markers?

Also, we need a magical reason to have the background radiation.
No, we don't as I have explained in my last post. MikeS, Sat, 20th Aug 2011

quote PhyzBang

Expansion causes time dilation.

You might have a point there would you care to elaborate on it? MikeS, Sat, 20th Aug 2011

Mike, time on average is probably constant. Just before the Bigbang, gravity was at its maximum but kinetic energy was zero. Now, a part of gravitational energy is in kinetic energy. Before the Bigbang, it was all GR time dilation and now it is part GR and part SR... Relativity has almost been entirely proven.

Expansion of space, which is not kinetic energy, is causing an increase in time dilation, but i suspect it is redundant to Relativity. Relativity is relative... :o) Expansion of space could be the dark energy???

If there is dark energy and the universe expansion is truly accelerating, it would probably mean that time is dilating over time... Which, from an entire universe point of view, is improbable but not impossible; meaning there is probably an unknown part of the universe causing dark energy to our visible universe (if it is not space expansion)... CPT ArkAngel, Sat, 20th Aug 2011

The redshift of cosmological expansion results from time dilation between the source of light and our observation of that light. Cosmological expansion cannot help but introduce a significant difference between the rest frames of distant objects. Many people erroneously attribute cosmological redshift to the Doppler effect but the Doppler effect is not the origin of cosmological redshift.

When we look at events of known length, we can see this time dilation at work. It's the same amount as that which would cause redshift from cosmological expansion.

One of the great pieces of evidence for expansion is the background radiation. This is not simply because it is extremely redshifted; it is because it is evidence that the universe was incredibly dense in the far past. A global field of time dilation with no source and no expansion could have no connection with a dense past of the universe. PhysBang, Sat, 20th Aug 2011

Hasn't the Red Shift system of measuring speed been proven to be wrong?  Thanks for comments.  Joe L. Ogan Joe L. Ogan, Sat, 20th Aug 2011

That depends on what you mean by "Red Shift system of measuring speed". A shift in the spectrum of light or sound is regularly and reliably used to detect motion and calculate speed in many different circumstances. All techniques have potential systematic errors (and statistical errors akin to simple bad luck) that can be controlled to a greater or lesser extent. PhysBang, Sat, 20th Aug 2011

Why is the universe expanding?

To me this a simple answer. All stars in the universe are expelling energy.  This energy acts like a rocket firing in all directions.  The reactive mass(?) of all the stars are propelling each and everyone away from each other.

Think of a rocket with an almost infinite supply of energy (well if we humans were building one).  This rocket in theory will accelerate and accelerate eventually maxing out at a predefined speed.

THIS CONSTANT (for now) NUCLEAR FORCE IS ACCELERATING THE EXPANSION OF THE UNIVERSE!!!

Sorry about the caps, i wanted to emphisize that.  Now, im no physics expert but basic GSCE (and Discovery channel) knowledge seems to point me in this rather basic explanation of why the universe is expanding.

Feel free to comment on why i may be mistaken, but take a minute to think about the research being done on 'Solar Sails'.

Looking forward to hear what you guys have to say? i do hope this hasnt been covered numerous times!!! mattyh, Sat, 20th Aug 2011

The redshift of cosmological expansion results from time dilation between the source of light and our observation of that light. Cosmological expansion cannot help but introduce a significant difference between the rest frames of distant objects. Many people erroneously attribute cosmological redshift to the Doppler effect but the Doppler effect is not the origin of cosmological redshift.

When we look at events of known length, we can see this time dilation at work. It's the same amount as that which would cause redshift from cosmological expansion.

One of the great pieces of evidence for expansion is the background radiation. This is not simply because it is extremely redshifted; it is because it is evidence that the universe was incredibly dense in the far past. A global field of time dilation with no source and no expansion could have no connection with a dense past of the universe.


All this says is that the effects of cosmological expansion and time dilation look the same which is what I have been arguing all along.

Expansion does not cause time dilation.  They just look the same.

But a dense past implies a high gravitational field which would be accompanied by time dilation so there is a connection.  I have explained the mechanism in part (3) of Is cosmological time a constant? in new theories below
"As the universe cooled further much of the energy was converted into simple atoms.  The universe went from energy dominated to matter dominated.  The passage of time went from near infinite to slow."
http://www.thenakedscientists.com/forum/index.php?topic=40685.msg365375#msg365375 MikeS, Sun, 21st Aug 2011



This is essentially what I proposed in this post in new theories
Is this the cause of cosmological expansion.
http://www.thenakedscientists.com/forum/index.php?topic=40531.msg364500#msg364500 MikeS, Sun, 21st Aug 2011



Now I would have thought that as there was no mass, there would be no gravity.  Likewise, after the big-bang there would still be no gravity until the universe had cooled sufficiently for plasma (mass) to form.

I just can't see that.  From our perspective they look the same.  That doesn't mean one is the cause of the other.  Is there any evidence for this?

Why would we assume that?  Universal time varies locally why assume it is any different on a cosmological time scale.  This would seem to imply that whatever causes the universes master clock to tick at a given rate is constant and unchanging.  The Universe is dynamic and constantly changing but on a cosmological time scale.  Also, as I have mentioned previously, the discrepancy in relative brightness to red-shift in type 1a supernova would seem to imply that clocks actually did tick slower in the past. MikeS, Sun, 21st Aug 2011

Quote
Expansion causes time dilation.

The Universe is supposedly expanding and that expansions is accelerating.  Supposedly, the universe is expanding at the speed of light.

As there are no preferential frames of reference, we must be travelling at the speed of light.

This would account for extreme time dilation.  Why aren't we frozen in time?  MikeS, Sun, 21st Aug 2011

3 pages in, and nobody has pointed out that one reason for assuming that the universe is expanding is that we know it can't be constant. Bored chemist, Sun, 21st Aug 2011



Very good point but it could be contracting. MikeS, Sun, 21st Aug 2011



Dare I say it, this could be interpreted as evidence against cosmological expansion and evidence if favour of time dilation. MikeS, Sun, 21st Aug 2011

First, you have to accept that there is no singularities, which is more mainstream than the BigBang Theory... What i call gravity at the bigbang is the binding energy: the Unified Force.

Second, you have to accept the high probability that it was a black hole that suffer a breaking in its symmetry, not negative energy  causing the expansion, simply because there was a time before time, meaning that the black hole of origin is a condensed of a past universe (no negative energy needed, just a breaking of symmetry, instability:too much matter, or a collision). This has convert a great amount of the binding energy into kinetic energy, i think half of it (see my theory).

The expansion of space is the kind of pseudo-force that makes the universe expand allegedly faster than light.

I said time on average, not time everywhere in the universe. Time dilation is due to two things, relative velocity (SR) and gravity (GR). The average timerate is proportional to the energy of the universe. The unified force of the black hole contains the entire energy of the universe. Energy is conserved, thus time on average is constant...

So the expansion of space, if there is one, is like an excess of kinetic energy or a negative energy...

The objects velocities observed are higher the farther away the objects are from us. This leads to the Dark Energy theories. But it could be simply a matter of non uniformed distribution of kinetic energy. The farther away objects are, the more kinetic energy they got from the bigbang... CPT ArkAngel, Sun, 21st Aug 2011


ONLY FOR COSMOLOGICAL REDSHIFT. There is also the change in average density and the development of large scale structure over time. A change in time dilation does not make things less dense.

Where did this density go? Did it magically disappear? PhysBang, Sun, 21st Aug 2011


ONLY FOR COSMOLOGICAL REDSHIFT. There is also the change in average density and the development of large scale structure over time. A change in time dilation does not make things less dense.

Where did this density go? Did it magically disappear?


I agree, a change in time dilation does not make things less dense, I never said it did.  I addressed this point in
http://www.thenakedscientists.com/forum/index.php?topic=40685.msg365375#msg365375
I believe inflation took place in the early universe and that inflation rolled off to become a much slower expansion.  My point being, you can't tell the difference between cosmological expansion and time dilation in which case our estimates of cosmological distance and how old the universe is may be considerably off.  Also as mentioned in the above link
"When we ask how old is the Universe?  Is this a meaningful question if the passage of time is variable?  It's like measuring length with a piece of elastic."

"Where did this density go? Did it magically disappear?"
I have already addressed this in the above link.
"3a)   Inflation rolls off turning into a more sedate expansion." MikeS, Mon, 22nd Aug 2011

CPT
Assuming there may be more than one theory, which one? Link please. MikeS, Mon, 22nd Aug 2011


So, essentially you want to throw away all the evidence we have for expansion, except where it's convenient for your own pet theory. Gotcha. PhysBang, Mon, 22nd Aug 2011


So, essentially you want to throw away all the evidence we have for expansion, except where it's convenient for your own pet theory. Gotcha.


As you are well aware I only wrote that post as I could not mention its contents in this thread.  It was written in response to your query as to why the passage of time could vary.  It was written as a courtesy to you but is essentially irrelevant to the arguments in this thread.

Not at all.  I have never maintained that the universe is not expanding.  What I have maintained all along is there is precious little (if any) evidence for expansion that can not also be explained by time dilation.  I have asked you to point out any evidence that I might have missed. 
quote PhysBang
"We can measure features of expansion in many different ways."
My answer "What ways, other than those I have already mentioned and explained, namely:-
red-shift, type 1a supernova, CBR, Olbers paradox and short to mid range cosmological markers?
This you have failed to do (other than in extremely general terms).  I have answered all of your points politely despite that fact that I have to keep repeating myself whilst ignoring your condescending attitude and sarcasm.  Now, it would seem, you have run out of arguments, pity but I understand.

As I said in my last post
"My point being, you can't tell the difference between cosmological expansion and time dilation in which case our estimates of cosmological distance and how old the universe is may be considerably off." MikeS, Mon, 22nd Aug 2011

This thread has turned into a springboard for promoting new theories and is becoming uncivil.  I'm locking it. jpetruccelli, Mon, 22nd Aug 2011

See the whole discussion | Make a comment


-
Not working please enable javascript
EPSRC
Powered by UKfast
STFC
Genetics Society
ipDTL