Looking for other proof of expanding universe.

[grounded]

The idea of an expanding universe is said to be proven by using the calculated distance of a Cepheid star from us, and the amount of change in the wavelengths of light emitted from the Cepheid star relative to us.

There must be another way to prove the universe is expanding since the above is only proof if you assume that the change in wavelength is caused by the expansion of space. Is anyone aware of another method used to prove the expansion? Has anyone measured the distance of the same Cepheid star several years apart?

 

[Vanadium 50]

Did you look at the Frequently Asked Cosmology Questions? Is there something in particular that you find difficult?

 

[Drakkith]

The idea of an expanding universe is said to be proven by using the calculated distance of a Cepheid star from us, and the amount of change in the wavelengths of light emitted from the Cepheid star relative to us.

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.

Here is a link to the cosmological distance ladder. It lists the various methods that we use to determine the distance to objects in space. http://en.wikipedia.org/wiki/Distance_ladder
You can see that there are many different ways of measuring distance. Having more than one way to measure the distance to an object, similar to what I said above, allows us to be confident that our techniques are indeed correct.

There must be another way to prove the universe is expanding since the above is only proof if you assume that the change in wavelength is caused by the expansion of space. Is anyone aware of another method used to prove the expansion? Has anyone measured the distance of the same Cepheid star several years apart?

The idea of a doppler shift in the wavelength of light is VERY strongly supported by all current scientific theories. We can actively measure redshift in a lab to a very high precision. When we apply that to our observations of the universe, we find that things are moving away from us. Our interpretation of this recession uses General Relativity, the most accurate theory dealing with gravity and very large scale objects like galaxies, clusters, etc. GR explains gravity as emerging from the geometric properties of spacetime. It is the framework of GR that allows us to explain the recession of galaxies away from us as an "expansion of space".

Also, the amount of observations performed in astronomy are staggering. Not only by professionals, but by amateurs as well. Here is a light curve for the star Mira for the last 20,000 days, since 12 Jan 1958.

http://www.aavso.org/tmp3/468617438.png

I pulled this from the AAVSO website in about 30 seconds. http://www.aavso.org/lcg
So yes, we have observed variable stars over the course of several years. If you want to find data on a specific Cepheid variable just use the light curve generator at the link above.

 

[Chronos]

We also have observational evidence the universe was cooler in the past, which is precisely what you would expect in an expanding universe - re: http://arxiv.org/abs/1012.3164, and http://www.das.uchile.cl/das_ingles/new_temp_measurements.php .

 

[Drakkith]

Chronos you mean warmer?

 

[Chronos]

I plead dyslexia.

 

[Drakkith]

I plead dyslexia.

There's no pleading in Cosmology!

 

[Chronos]

Cosmology is cruel.

 

[Drakkith]

Cosmology is cruel.

Cruel Cosmology, now offered at a college near you!

 

[Chronos]

OMG, I think I am teaching that course! They will not take me alive.

 

[urmother]

universe is not expanding only the galaxies are moving away from each other..like the shards after an explosion .space is infinite hard vacuum and these matter and energy is expanding into this nothingness and creating the familiar space that we know of ie space with underlying vacuum energy .UNIVERSE is not expanding !



like in the above video the particles will move away from each other like normally would after an explosion ,space is not expanding ,if the movement of galaxies is because of expansion of space ,then all galaxies will be moving away from each other in same speed

.idk why people invoke this kind of esoteric metric expansion like weird ideas .

 

[Drakkith]

universe is not expanding only the galaxies are moving away from each other..like the shards after an explosion .space is infinite hard vacuum and these matter and energy is expanding into this nothingness and creating the familiar space that we know of ie space with underlying vacuum energy .UNIVERSE is not expanding !

This is wrong. You are under the impression that galaxies are moving away from us due to an explosion within space back at the "big bang". This is a classic misconception.

like in the above video the particles will move away from each other like normally would after an explosion ,space is not expanding ,if the movement of galaxies is because of expansion of space ,then all galaxies will be moving away from each other in same speed

.idk why people invoke this kind of esoteric metric expansion like weird ideas .

Incorrect. Expansion is the only thing that explains the observed recession velocities. An explosion within space absolutely does not. And that video is not a realistic depiction of a grenade exploding, it is simply a movie someone made just to make it. In a real explosion smaller fragments are ejected at very high velocities while larger fragments are slower thanks to their larger mass. That video has them all intermixed.
See here: http://www.phinds.com/balloonanalogy/

Keep in mind that the redshift measured increases linearly with the distance of an object. An explosion within space would NOT do this.
At the time of the big bang, everything was in the form of radiation and subatomic particles. A normal explosion would have pushed the lighter particles away faster than the heavier ones and would have had no affect on the radiation.
We routinely measure recession velocities of objects that exceed the speed of light. If it were a normal explosion that caused the expansion this would be impossible per the rules of Special Relativity. Luckily for us General Relativity trumps SR and allows recession velocities to exceed c if they are non-local and due to the geometric properties of space. (IE if they are caused by expansion, not movement through space)

 

[PeterJ]

I heard recently that different frequencies of radiation have been measured to travel at different speeds on their way through space to us. Is it possible that this bias in the arrival time of different frequencies could affect our measurement of distances to objects?

 

[Chronos]

I heard recently that different frequencies of radiation have been measured to travel at different speeds on their way through space to us. Is it possible that this bias in the arrival time of different frequencies could affect our measurement of distances to objects?

A frequency dependent speed of light has been postulated under a variety of cosmological models. No such effect has been detected to date.

 

[codex34]

Expansion is the only thing that explains the observed recession velocities.

Incorrect. Expansion is currently the only thing that explains the observed recession velocities.

the assumption that redshifts are not velocity shifts is more economical and less vulnerable, except for the fact that, at the moment, no other satisfactory explanation [i.e., apart from the Doppler effect] is known.

There are exceptions to the rule, and unexplained observations with galactic velocity fields that call into question expansion as an explanation of redshift.
But seeing as there are no explanations forthcoming, expansion will have to do as a model for now, although it is fun trying to come up with alternatives, that's for other threads though.

 

[PeterJ]

A frequency dependent speed of light has been postulated under a variety of cosmological models. No such effect has been detected to date.

Not according to the glossy TV documentary I watched a couple of weeks ago. They reported well-observed and significant effects and discussed them with the researchers. All quite excited about it. I don't think I dreamt it but you never know.

 

[Drakkith]

Incorrect. Expansion is currently the only thing that explains the observed recession velocities.

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

There are exceptions to the rule, and unexplained observations with galactic velocity fields that call into question expansion as an explanation of redshift.
But seeing as there are no explanations forthcoming, expansion will have to do as a model for now, although it is fun trying to come up with alternatives, that's for other threads though.

What exceptions are you referring to?

Not according to the glossy TV documentary I watched a couple of weeks ago. They reported well-observed and significant effects and discussed them with the researchers. All quite excited about it. I don't think I dreamt it but you never know.

TV documentaries are notoriously prone to giving out highly speculative and often incorrect information. Do not take them seriously unless you can find the same information from multiple sources, preferably peer reviewed sources.

 

[marcus]

Not according to the glossy TV documentary I watched a couple of weeks ago. They reported well-observed and significant effects and discussed them with the researchers. All quite excited about it. I don't think I dreamt it but you never know.

To elaborate on what Drakkith said, here is a constructive suggestion: You say they discussed the findings with the researchers! Another time if you could jot down the names of one or more of those who did the research, we could look their papers up.

It's normally easy to do if you have the name and first initial of one of the authors.

A celebrity scientist merely commenting on some younger person's work isn't usually very helpful. But if you give us the name of one of the researchers we might be able to find the actual scientific publication online.

There have been some false alarms---seemingly exciting results that were not confirmed---so it's helpful to be able to find the particular announcement and publication that they were talking about.

 

[marcus]

Is anyone aware of another method used to prove the expansion? Has anyone measured the distance of the same Cepheid star several years apart?

Grounded, are you still around?
The current rate of expansion is 1/139 of one percent every million years. It sounds like you are asking that someone measure the distance to a star to within an accuracy of 1/139 of one percent, and then wait a million years and measure it again that accurately, to see if it is then farther away by that fraction of a percent.

But actually astronomers do better than this all the time! For example with type 1A supernovae.

These are all about the same intrinsic brightness and they follow the same approximate schedule day by day. Changing brightness and color. About 15 days to reach peak brightness, then falling off at a certain rather rapid rate for about 25 days, then dimming at a much more gradual rate for another 40-some days. The color changes are more subtle but detectable---different bands change according to a slightly different profile over time.

With a z=1 supernova of this type, for example, we get the news of its day 5 LATER, because by the time it is doing its day 5 stuff (which is recognizable and we expect) it is FARTHER.
So the news of what it was doing on day 5 only reaches us on day 10. Because it had to travel farther.

We know to expect the peak brightness around day 15, but during the first 15 days of its explosion the star got farther away. So the news had farther to travel and we only get the news on day 30 of watching.

This is essentially what you were asking people do with Cepheids, observe one now and then a while later to see if it has moved farther. Well YES, effectively this is done with that type of supernova.

The watching schedule is retarded (compared with the explosion schedule) by the star getting day by day farther away and the news needing more time to get to us.

 

[urmother]

This is wrong. You are under the impression that galaxies are moving away from us due to an explosion within space back at the "big bang". This is a classic misconception.

Incorrect. Expansion is the only thing that explains the observed recession velocities. An explosion within space absolutely does not. And that video is not a realistic depiction of a grenade exploding, it is simply a movie someone made just to make it. In a real explosion smaller fragments are ejected at very high velocities while larger fragments are slower thanks to their larger mass. That video has them all intermixed.
See here: http://www.phinds.com/balloonanalogy/

Keep in mind that the redshift measured increases linearly with the distance of an object. An explosion within space would NOT do this.
At the time of the big bang, everything was in the form of radiation and subatomic particles. A normal explosion would have pushed the lighter particles away faster than the heavier ones and would have had no affect on the radiation.
We routinely measure recession velocities of objects that exceed the speed of light. If it were a normal explosion that caused the expansion this would be impossible per the rules of Special Relativity. Luckily for us General Relativity trumps SR and allows recession velocities to exceed c if they are non-local and due to the geometric properties of space. (IE if they are caused by expansion, not movement through space)

the site you linked to says this

if expansion of galaxy clusters are "UNIFORM" in all direction then it is conclusive indication that galaxy clusters are indeed expanding due to metric expansion of space .

http://astro.unl.edu/classaction/animations/cosmology/balloon.swf

but unfortunately that is not the case ,different clusters are expanding itself and moving away from other clusters of the "cosmic web" at DIFFERENT rate

now imagine you blowing a balloon and the pennies glued to the surface of balloon are NOT uniformly moving away from each other ?how weird would that be ?

 

[Drakkith]

but unfortunately that is not the case ,different clusters are expanding itself and moving away from other clusters of the "cosmic web" at DIFFERENT rate

No, they are not. The RATE is the same for all of them, the VELOCITY is different. Rate is a ratio between two numbers, such as the increase in distance between two galaxies and the time it takes for that to happen. The rate of expansion determines how long it takes for distances between everything to double. Galaxies further away from each other move further away in total distance and have a greater recession velocity, but they end up TWICE as far away at the same time as everything ends up twice as far away.

 

[PeterJ]

TV documentaries are notoriously prone to giving out highly speculative and often incorrect information. Do not take them seriously unless you can find the same information from multiple sources, preferably peer reviewed sources.

Yes, this is why I brought it up here.

 

[Lino]

... With a z=1 supernova of this type, for example, we get the news of its day 5 LATER, because by the time it is doing its day 5 stuff (which is recognizable and we expect) it is FARTHER.
So the news of what it was doing on day 5 only reaches us on day 10. Because it had to travel farther.

We know to expect the peak brightness around day 15, but during the first 15 days of its explosion the star got farther away. So the news had farther to travel and we only get the news on day 30 of watching. ...

Marcus, Can I just confirm, are you saying that for a particular such explosion, with a particular z, the timing difference between the expected day 5 events and the expected day 15 events is growing at a significant rate (i.e. it can reasonably be observed - not the 1/139% over a million years)?

I would have expected that, for a particular explosion, the difference in timing between the day 5 and day 15 events would have been 10 day plus a tiny (unmeasurable) amount.


Regards,


Noel.

 

[George Jones]

Not according to the glossy TV documentary I watched a couple of weeks ago. They reported well-observed and significant effects and discussed them with the researchers. All quite excited about it. I don't think I dreamt it but you never know.

Do you remember the documentary's title (in whole or part)? On what network it was broadcast?

I would love to track it down.

 

[marcus]

Marcus, Can I just confirm, are you saying that for a particular such explosion, with a particular z, the timing difference between the expected day 5 events and the expected day 15 events is growing at a significant rate (i.e. it can reasonably be observed - not the 1/139% over a million years)?

I would have expected that, for a particular explosion, the difference in timing between the day 5 and day 15 events would have been 10 day plus a tiny (unmeasurable) amount.Regards,Noel.

The reason is that the base distance you are calculating a percentage of is large. I will only do a crude approximate calculation using simple percentages.
First, what was the recession rate back at z=1? You know that corresponds to a stretch ratio 1+z which in Jorrie's calculator is called S. In this example S=2 (wavelengths get doubled on their way to us.)
So go here:
http://www.einsteins-theory-of-relativity-4engineers.com/CosmoLean_A25.html
put a 2 in the upper limit box, and press calculate.

You will see that the LOOKBACK time is approximately 8 billion years. This is the time it takes light to reach us from the explosion.

A small fractional change in DISTANCE THEN will correspond to roughly the same small fractional change in Lookback time. Placing an event farther away increases the time it takes light to reach us.

But you will also see that from the same calculator output table that the HUBBLE TIME back then was about 8 billion years.

So when you let one day pass during the explosion distance then increases by the fraction (1 day)/(8 billion years)

And that causes the lookback time to increase by about the same fractional amount.
The lookback time is 8 billion years and the fraction is (1day)/(8 billion years). Multiply the two together and you get 1 day.

So the news reaches us after TWO DAYS, for two reasons: we are watching the second day of the explosion so the event occurred one day later, but also what we are watching was FARTHER by a certain small fractional amount and so the time it took light to reach us was one day more.

The second effect you can think of as a direct experience of expansion. Distances to galaxies increase and so we can compare this way and see that a day later the galaxy we are looking at is a certain amount farther----because the light took longer to reach us.

I only say this to respond to that guy's (Mr. Grounded) OP question. He said could we look at a Cepheid some years later and tell it was farther. I think we could but I don't know of the research. However astronomers also use Supernovae the same way, as distance marker "standard candles". And they are ALWAYS looking at the 60 day lightcurve history of the explosion. And they are ALWAYS seeing that history get stretched out (by Jorrie calculator "stretch ratio" S, or by 1+z if you like). So I'm telling that guy yes we do see this all the time, but with Supernovae, if not with Cepheids. It comes free with them and would be more work and take more time with Cepheids, I think.

The schedule of natural process gets stretched just the same ratio the lightwaves get stretched.

We know the 60 day schedule of Type 1A SN explosion from watching near ones which are not stretched out so much. The Type 1As are all pretty much the same (as you know but the OP Mr. Grounded may not) because they blow at a critical mass and so that is why they are used as standard-brightness "candles" to mark distance.

 

[Lino]

Marcus, I appreciate that the effect of expansion on the timings of processes is "old hat" to you (and I assume many others) but it is news to me (and I thought that I knew / read a lot on the subject). Much, much appreciated. Wow.

I'll read some more papers on type 1a's, but do you know of other cosmological events, with known process timings, that I could read about to understand it more?

(I have to say, including redshift, the four pillars, etc., this is by far and away the best evidence for expansion that I've come across. I want to consider it further, but wow!)

Again, very much appreciated.

Regards,

Noel.

 

[marty1]

The universe is expanding. I think what confuses most people (including me, but I think I have a grasp now) is that it is expanding ~like~ it would have expand if it exploded from a big bang (so it is easy without math to say it was "just" an explosion), but everything is moving away from everything else with a force that cannot be explained by the model of an explosion of everything from a central point. That is the expansion that throws you off. This force is weak--too weak to rip apart atoms, so the stuff we are made of is not flying apart and our planet it safe... just getting farther away from far away things faster than local velocities could explain.

 

[Drakkith]

The universe is expanding. I think what confuses most people (including me, but I think I have a grasp now) is that it is expanding ~like~ it would have expand if it exploded from a big bang (so it is easy without math to say it was "just" an explosion), but everything is moving away from everything else with a force that cannot be explained by the model of an explosion of everything from a central point.

What part of the expansion is able to be explained by an explosion within space? To my knowledge it simply isn't able to be explained in such a way. For example, I don't think a normal explosion could explain the linear increase in velocity as distance increases.

 

[marty1]

What part of the expansion is able to be explained by an explosion within space? To my knowledge it simply isn't able to be explained in such a way. For example, I don't think a normal explosion could explain the linear increase in velocity as distance increases.

J.C. I said it can't be explained. I said to the observer it would looks like that. A bunch of separate stuff getting farther and farther away from each other.

 

[Drakkith]

J.C. I said it can't be explained. I said to the observer it would looks like that. A bunch of separate stuff getting farther and farther away from each other.

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?

 

[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.

On Physics Forums, this has to be done within the rules of Physics Forums

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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.