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Looking for other proof of expanding universe.

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

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 Quote by Drakkith 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.

 Quote by Drakkith 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.

 Quote by Drakkith 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?

 Quote by Drakkith 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.
 Quote by Drakkith 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.

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 Quote by zonde 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.

 Quote by Drakkith 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.

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 Quote by marty1 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.

 Quote by Drakkith 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)?

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 Quote by marty1 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.

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 Quote by Drakkith 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?

 Quote by Drakkith 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.

 Quote by Drakkith It doesn't matter if I observed it before I made the hypothesis or not.
 Recognitions: Gold Member 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.
 Recognitions: Gold Member Science Advisor marty1, whatever point you were trying to make has become too illogical to even merit a comment. Apparently zonde has attempted to 'rescue' whatever it was you thought you 'discovered'. It's flat wrong, so, just get over it.

 Quote by Chronos marty1, whatever point you were trying to make has become too illogical to even merit a comment. Apparently zonde has attempted to 'rescue' whatever it was you thought you 'discovered'. It's flat wrong, so, just get over it.
It was a question. Questions cannot be wrong. Only your answer can be right or wrong.
 Please allow me to simplify my question then. How can an observer using only the one way travel of light from a distant source distinguish between the acceleration of the source from a relativistic dilation of length and time that varies over time?

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 Quote by 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.
To have any meaningful discussion we have to have some common base that we accept without doubt. In science this common base is scientific method.

Certainly you agree with that, right?

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 Quote by marty1 Please allow me to simplify my question then. How can an observer using only the one way travel of light from a distant source distinguish between the acceleration of the source from a relativistic dilation of length and time that varies over time?
You want to compare absolute (flat) source in flexible spacetime with flexible source in flat spacetime?
Or are you talking about ordinary acceleration of source like with applied force and everything (and flat spacetime)?

 Quote by zonde You want to compare absolute (flat) source in flexible spacetime with flexible source in flat spacetime? Or are you talking about ordinary acceleration of source like with applied force and everything (and flat spacetime)?
No, not compare, receive a signal and know how much each of those two extremes contributed to changing it from what left the source (one way).

How do I distinguish the effects of the intervening and changing (important part) curved space-time over vast distances from the acceleration of the source?

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 Quote by zonde To have any meaningful discussion we have to have some common base that we accept without doubt. In science this common base is scientific method. Certainly you agree with that, right?
Yes.
 Can I just point out that the distance to redshift relationship is inferred, it isn't an actual observation. The magnitude versus redshift is the best fit relationship and distance is inferred from this and other assumptions. There is also an Angular size to redshift relationship, which fits non expanding euclidean space!!! http://www.wissenschaft-in-not.de/kosm003e.htm The magnitude, luminosity, angular size, and distance relationships all have their problems with assumptions, such as the magnitude being an average of luminosity in watts/area, which doesn't account for an objects shape. You can't say redshift is PROOF of anything, the method of measurement used to produce the redshift is archive based, a comparison against other observations, it's relationship to anything else is inferred. I recently read a paper that measured the velocity field for certain edge on galaxies, one small statement really stood out, 'on turning the slit 90° no velocity field was found' - WHY? Isn't the shift in spectrum embedded in the light? The statement that expansion is the only correct model shouldn't be made, it is simple our current model, we have other things to investigate and bigger telescopes to build before making such statements. How many people know what a parabolic caustic is? How many people can calculate them? How many people think light is parallel?, or as effectively parallel to ignore any angle?