Looking for other proof of expanding universe.

[codex34]

When discussing science one should always take for granted that if someone says something, the phrase "as far as we know" is implied..

Sorry, just being pedantic, but you know, that is the first time I've seen the implication on a physics forum, usually it's 'current theory is correct and proven beyond doubt, don't talk about anything else', breath of fresh air.

The exceptions are those controversial ones, which one the face of it have been debunked, so really I should correct myself by saying, they might, until proven otherwise, be exceptions, but I find both sides at fault, both sides are sometimes looking for, and seeing, only what they want to.
I personally don't accept, fitting to a model, based on assumptions, as proof of anything, except for cheese.
I don't see what's so wrong in having a closer look.

 

[George Jones]

I personally don't accept, fitting to a model, based on assumptions, as proof of anything, except for cheese.

Science never proves anything.

I don't see what's so wrong in having a closer look.

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[Drakkith]

I personally don't accept, fitting to a model, based on assumptions, as proof of anything, except for cheese.
I don't see what's so wrong in having a closer look.

All science both fits to a model and is based on assumptions to some extent.

 

[marty1]

I think I see the issue. You said is expands "like" it would from an explosion. Well, obviously this isn't true, but for someone who hasn't ever seen the data, it can seem like it does. Is that the gist of what you were getting at?

That was exactly my jist.

 

[Chronos]

The problem with the 'exploding' model stems from Newtonian mechanics, where low mass particles acquire higher velocities than high mass particles from an initial 'explosion'. This works well for a classical universe, where momentum is always conserved, but, is wildly inconsistent with GR and observational evidence.

 

[zonde]

There is also the redshift of supernovas, quasars, etc. A very good indicator is type 1a supernovas, since they all seem to the same mass at the time of the explosion, their intrinsic brightness is the same. So the brighter an observed 1a SN is, the closer it is too us. This matches with the measured redshift of objects at that distance in accordance with hubbles law. IE we measure the brightness and redshift of a type 1a supernova and BOTH of the measurements fit our expectations and predictions. Correlating two different effects let's us be much more confident that our model is correct.

Only you forgot to add that brightness and redshift does not agree within available precision of measurements. That's the very thing that is behind the idea of accelerated expansion. So this effect can't serve too well as experimental confirmation of cosmological expansion.

I believe that apparent time dilation of highly redshifted objects is the thing that makes people more confident in cosmological expansion.

 

[Drakkith]

Only you forgot to add that brightness and redshift does not agree within available precision of measurements. That's the very thing that is behind the idea of accelerated expansion. So this effect can't serve too well as experimental confirmation of cosmological expansion.

I believe that apparent time dilation of highly redshifted objects is the thing that makes people more confident in cosmological expansion.

No, those still serve perfectly fine for expansion evidence. It just turns out that they are also evidence for an accelerating expansion.

 

[zonde]

No, those still serve perfectly fine for expansion evidence. It just turns out that they are also evidence for an accelerating expansion.

Given redshift of standard candle how are you going to calculate prediction for observed luminosity?

 

[Drakkith]

Given redshift of standard candle how are you going to calculate prediction for observed luminosity?

The same way it was done before we realized the expansion was accelerating? I don't understand how redshift of standard candles isn't evidence for expansion? If they are redshifted, then they are moving away, correct?

 

[Lino]

The same way it was done before we realized the expansion was accelerating? I don't understand how redshift of standard candles isn't evidence for expansion? If they are redshifted, then they are moving away, correct?

There are other explanations, but the standard model tells us that when it is combined with other evidence (the four pillars) there are few possibilities.

I need to start this next paragraph with an apology to previous contributors to this thread - who I thanked, and still do, most sincerely. However, I need to ask a related question: if we measure the redshift of an object (say a particular standard candle), and then re-measure it may years later, I would expect to see the redshift and distance increasing. Unfortunately, I understand that with current technologies this would take significantly longer than we have been measuring. An alternative approcah, using the timings associated with the light curve of a distant SN1a was mention and this sounded very promising. Unfortunately, I have not been able to find any papers / evidence that this is being looked at. So to my question: is anyone familiar with work looking at the timing associated with the light curves of SN1a's (or other "standard" cosmological process)?


Regards,


Noel.

 

[marty1]

The problem with the 'exploding' model stems from Newtonian mechanics, where low mass particles acquire higher velocities than high mass particles from an initial 'explosion'. This works well for a classical universe, where momentum is always conserved, but, is wildly inconsistent with GR and observational evidence.

Mind you, am not implying an exploding model, ony use it as the "intuitive" model that makes learning the correct model more difficult. After all, if your intent is to teach someone the correct model it is better to understand the barriers that stand in their way. If the intent is only to mock people who do not understand the truths of the universe as you do, then, well, I can't help you there beyond recommending a good therapist.

However, with that said, I don't think that even Newtonian mechanics itself is enough to discard an exploding model if everything at the moment it was given its initial velocity was exactly identical. There were yet no particles.

 

[Drakkith]

However, with that said, I don't think that even Newtonian mechanics itself is enough to discard an exploding model if everything at the moment it was given its initial velocity was exactly identical. There were yet no particles.

How would you reconcile this with observations of everything expanding away from everything else? This would imply that we are at the center of the universe, would it not? Also, I believe there were in fact plenty of particles at this point in time, it's just that it was so hot and dense they were being created and annihilated constantly. If there were no particles an explosion would have done nothing, as there would have been nothing to expand outwards since explosions don't affect EM radiation. Wouldn't we then have to invent a way for particles to be created with their velocities?

 

[marty1]

How would you reconcile this with observations of everything expanding away from everything else? This would imply that we are at the center of the universe, would it not? Also, I believe there were in fact plenty of particles at this point in time, it's just that it was so hot and dense they were being created and annihilated constantly. If there were no particles an explosion would have done nothing, as there would have been nothing to expand outwards since explosions don't affect EM radiation. Wouldn't we then have to invent a way for particles to be created with their velocities?

Why does it still sound like you guys are arguing against an exploding model of a big bang when I am not arguing as a proponent of such? I am explaining the bias that must first be overcome in the new learner before non-intuitive expansion (for which you have no good reason for other than excepting it faithfully from observation) can be accepted.

Perhaps the better approach would be to actually build a model that follows incorrect thinking and show exactly the points where it breaks down.

 

[Drakkith]

Why does it still sound like you guys are arguing against an exploding model of a big bang when I am not arguing as a proponent of such? I am explaining the bias that must first be overcome in the new learner before non-intuitive expansion (for which you have no good reason for other than excepting it faithfully from observation) can be accepted.

Perhaps the better approach would be to actually build a model that follows incorrect thinking and show exactly the points where it breaks down.

I don't know. You've confused me with your last few posts.

 

[Chronos]

Explaining the problems with the 'exploding' model is not an affront without a volunteer to assume the role of the aggrieved party. What scientific basis other than 'excepting [sic] it faithfully from observation' would you suggest?

 

[zonde]

The same way it was done before we realized the expansion was accelerating? I don't understand how redshift of standard candles isn't evidence for expansion?

Well, expansion appeared as explanation for redshift. Therefore redshift is not an evidence of expansion.
Luminosity of standard candles however can be viewed as a test of expansion.

If they are redshifted, then they are moving away, correct?

This is the most direct interpretation of redshift. So you would expect that it will be assumed as a primary possible explanation even without any tests.
But on the other hand this interpretation of redshift leads to very exotic consequences and therefore I do not consider it likely.

 

[Drakkith]

Well, expansion appeared as explanation for redshift. Therefore redshift is not an evidence of expansion.
Luminosity of standard candles however can be viewed as a test of expansion.

That's ridiculous, you can't claim the 1st thing and then right after claim the 2nd thing as evidence. By your logic I could easily claim that expansion is the explanation for the luminosity of standard candles being what it is, so it's not evidence of expansion either. Luckily we get around these circular arguments by empirical evidence and making models! We say "What happens if we assume that redshift is the result of expansion?" and then do some math and make some observations. It turns out that every result so far has turned out to be in support of expansion. The distribution of matter, the CMB, and a multitude of other things only make sense if we view expansion as being correct. If you have a different theory and model that fully supports the observed results without resorting to expansion, feel free to publish it and then we can discuss it here.

This is the most direct interpretation of redshift. So you would expect that it will be assumed as a primary possible explanation even without any tests.
But on the other hand this interpretation of redshift leads to very exotic consequences and therefore I do not consider it likely.

The FACT is that we know several things that cause redshift. We can verify them in the lab. When we apply it to cosmology the result is that things are moving away from us. Using GR we interpret this recession to be due to the expansion of space for a number of reasons.

 

[ImaLooser]

Why does it still sound like you guys are arguing against an exploding model of a big bang when I am not arguing as a proponent of such? I am explaining the bias that must first be overcome in the new learner before non-intuitive expansion (for which you have no good reason for other than excepting it faithfully from observation) can be accepted.

Perhaps the better approach would be to actually build a model that follows incorrect thinking and show exactly the points where it breaks down.

Hmmm. Well, the error is in thinking that there is an explosion into empty space that had a center. I am always bothered when reading that the Big Bang came from a "point," which is probably not true.

I guess you could say that it appears from Earth that it is at the center of an explosion, but if you plot out the data for some star in Andromeda, or anywhere else, it also appears to be at the center. The Universe and the expansion are isotropic, that is they appear basically the same from every point. That's not consistent with the explosion idea.

You could also tell them that for many years (100,000?) there was no empty space at all in the Universe. It was completely packed with particles. The number of particles then is the same as now, but space got (much) bigger.

 

[George Jones]

There are other explanations, but the standard model tells us that when it is combined with other evidence (the four pillars) there are few possibilities.

Do you mean reasons other than expansion for redshift, or do you mean reasons other than accelerated expansion for the Type Ia supernovae data.

By giving up spatial homogeneity, Lemaitre-Tolman Bondi universes can account for the supernovae data, but these models cannot "simultaneously explain SNIa observations, the small-angle CMB, the local Hubble rate and the kinetic Sunyae-Zeldovich effect (Bull, Clifton and Ferreira, (2011)."¹

I need to start this next paragraph with an apology to previous contributors to this thread - who I thanked, and still do, most sincerely. However, I need to ask a related question: if we measure the redshift of an object (say a particular standard candle), and then re-measure it may years later, I would expect to see the redshift and distance increasing.

Not necessarily; for some objects, the redshift decreases.

Unfortunately, I understand that with current technologies this would take significantly longer than we have been measuring.

The PF thread is

If we watch a given galaxy over a long period, then, at any given time, redshift will be given by

z = \frac{R \left( t_o \right)}{R \left( t_e \right)}-1,
but z will change over time because t_o (for us) and t_e (for the observed galaxy) both change over time. If we could directly observe this effect, it would be a fantastic way to test our models of the universe!

We are close to being able to do this, but, for economic and other reasons, such a project won't start for several decades. Once started, the project would take a couple of decades to start to get good results. From

http://arxiv.org/abs/0802.1532:

we find that a 42-m telescope is capable of unambiguously detecting the redshift drift over a period of ~20 yr using 4000 h of observing time. Such an experiment would provide independent evidence for the existence of dark energy without assuming spatial flatness, using any other cosmological constraints or making any other astrophysical assumption.

Also, redshifts of individual objects don't necessarily increase with time. Figure 1 from the above paper plots redshift versus time. The three red curves are for objects in our universe. As we watch (over many years) a distant, high redshift object, A, we will see the object's redshift decrease, reach a minimum, and then increase. If we watch a much closer, lower redshift object, B, we see the object's redshift only increase.

Roughly, when light left A, the universe was in a decelerating matter-dominated phase, and when light left B, the universe was in the accelerating dark energy-dominated phase.

An alternative approcah, using the timings associated with the light curve of a distant SN1a was mention and this sounded very promising. Unfortunately, I have not been able to find any papers / evidence that this is being looked at. So to my question: is anyone familiar with work looking at the timing associated with the light curves of SN1a's (or other "standard" cosmological process)?

Light curves for supernovae are not the only things that are affected. Rates that photons leave objects are also dilated, which affects the luminosities of objects. This effect is not predicted by 'tired light' theories.

"Lubin and Sandage have used the Hubble Space Telescope to compare the surface brightness of galaxies in three distant clusters ... quite inconsistent with the behavior ... expected in a universe with 'tired light'. ...

This slowing has been confirmed for the rate of decline of light from some of the Type Ia supernovae used by the Supernova Cosmology Project ..."²

For the supernova stuff, Weinberg references

http://arxiv.org/abs/astro-ph/0104382.

¹ "Relativistic Cosmology", Ellis, Maartens, and MacCallum (2012)

² "Cosmology", Weinberg (2008)

 

[Lino]

Thanks George. It will take me a while to get through this, but it sounds like just what I'm looking for. (Especially in relation to Cosmology by Weinberg.)

I appreciate that there circumstances under which the redshif of objects can decrease, and I am not a fan of tieerd light theories, but could you give me a couple of lines in relation to the dilation of photon rate (so that I will know what I am looking for)?Regards,Noel.

 

[marty1]

This is just a question I thought of reading these posts. Could the increasing distance between galaxies and decreasing gravitational tension between them lead to a non-linear increase in the time needed to travel between them--acceleration even though they are independently at constant velocity locally?

 

[Drakkith]

This is just a question I thought of reading these posts. Could the increasing distance between galaxies and decreasing gravitational tension between them lead to a non-linear increase in the time needed to travel between them--acceleration even though they are independently at constant velocity locally?

What? I mean, they are already moving away with an increasing acceleration, and it's an expansion, so the distance increases faster than linear.

 

[zonde]

That's ridiculous, you can't claim the 1st thing and then right after claim the 2nd thing as evidence.

Not sure I understand what you are saying here. So let's see if we agree when I formulate it this way:
If you use some fact to arrive at hypothesis then you can't use the same fact as confirmation of your hypothesis.

Luckily we get around these circular arguments by empirical evidence and making models! We say "What happens if we assume that redshift is the result of expansion?" and then do some math and make some observations. It turns out that every result so far has turned out to be in support of expansion. The distribution of matter, the CMB, and a multitude of other things only make sense if we view expansion as being correct.

"makes sense" is subjective criterion and it is not exactly what we call scientific test.
You left out very important thing - prediction. It's not enough to do some math. It has to result in some predictions.

The FACT is that we know several things that cause redshift. We can verify them in the lab.

You mean, we know two things - recession of source from receiver and time dilation, right?
As there are no broad range wavelength converters, right?

When we apply it to cosmology the result is that things are moving away from us.

Yes, basically that's what I said about straight forward interpretation of redshift.

Using GR we interpret this recession to be due to the expansion of space for a number of reasons.

And that's the exotic part.

 

[Drakkith]

Not sure I understand what you are saying here. So let's see if we agree when I formulate it this way:
If you use some fact to arrive at hypothesis then you can't use the same fact as confirmation of your hypothesis.

Of course you can. You just can't use it as the only confirmation.

If I hypothesize, for whatever initial reason, that the universe is expanding then redshift is exactly the kind of thing we would expect. It doesn't matter if I observed it before I made the hypothesis or not. I make my hypothesis, make predictions, gather other evidence in addition to redshift through observations and tests, and then form my theory and model. If everything fits together and passes further tests and predictions, and no other competing theory can explain it as well and as simple as mine then it can be considered to be valid.

"makes sense" is subjective criterion and it is not exactly what we call scientific test.
You left out very important thing - prediction. It's not enough to do some math. It has to result in some predictions.

Exactly.

 

[marty1]

What? I mean, they are already moving away with an increasing acceleration, and it's an expansion, so the distance increases faster than linear.

What I am asking is whether you could be fooled into thinking you are accelerating if the time it took for light to travel between you and a reference point increased at a rate greater than would be calculated classically from your actual velocities you knew you left each other at some point in the past. Time dilation caused by the lower and lower gravitation tension in that empty space between you and the object you measure the distance to. Since the speed of the light can't change the extra time is expresses itself as a change in wavelength; in this case a red shift.

We interpret travel time as distance only because we know the speed of light is constant. If the travel time of light increases your only choice would be to say that the distance has increased even though it could be the time that is dilated and there is in fact no acellerative force being applied to either the source or the object.

What I am asking is whether there is any evidence that the amount of ambient gravitational field in an large empty area over a large empty space would cause a non-linear dilation of time as the area became less dense even though the objects vacating that region were moving at constant velocity. I think you would be forced to interpret the situation as acelleration if the travel time between 2 objects increased non-linearly even if the classical distance calculated from velocity over time was linear.

 

[Drakkith]

What I am asking is whether there is any evidence that the amount of ambient gravitational field in an large empty area over a large empty space would cause a non-linear dilation of time as the area became less dense even though the objects vacating that region were moving at constant velocity. I think you would be forced to interpret the situation as acelleration if the travel time between 2 objects increased non-linearly even if the classical distance calculated from velocity over time was linear.

No, if anything there would be a blueshift, not a redshift.

 

[marty1]

No, if anything there would be a blueshift, not a redshift.

Even if I reversed my assumptions on the dilation? If the time between was less than the classical distance would calculated (more efficient to travel through space with less ambient gravity)?

 

[Drakkith]

Even if I reversed my assumptions on the dilation? If the time between was less than the classical distance would calculated (more efficient to travel through space with less ambient gravity)?

I'm trying hard to understand what you are asking, and unlike Marcus or Chronos, I don't have enough knowledge and experience with GR and Cosmology to give you detailed and specific answers for all your questions. Still, I'm pretty sure that what you are asking is simply not the way it works. Perhaps someone with a bit more knowledge could answer it, as I don't feel I am knowledgeable enough to answer this without really stretching my basic understanding.

 

[zonde]

Of course you can. You just can't use it as the only confirmation.

And if you use it as the only confirmation then you can't consider your hypothesis confirmed, right?

If I hypothesize, for whatever initial reason, that the universe is expanding then redshift is exactly the kind of thing we would expect.

If you hypothesize that the universe is expanding for the very reason that we observe redshift then it is kind of ridiculous to say that redshift is exactly the kind of thing we would expect.

It doesn't matter if I observed it before I made the hypothesis or not.

It matters. Read about hindsight bias.

 

[Drakkith]

Sorry Zonde, I'm not going to argue with you any more. It isn't as simple as you are making it out to be. Redshift IS evidence for expansion when you take the whole model into account. Look at the whole picture, not just the part you want to see.