Any direct measure of Universe expansion via galaxy subtended angles?

[hkyriazi]

TL;DR

Is there anyone examining a large sample of galaxies' subtended angles over time, as an independent test of the universe's supposed expansion?

As indicated in the title and summary, I'm wondering if there is any large scale astronomical effort to assess directly the universal spatial expansion assumed by the Doppler interpretation of the redshift/distance relationship, by measuring individual galaxy subtended angles over time. The predicted decreases in size over time should be small, to be sure, but with a large enough sample size and good enough telescopes, may be measurable over a 5-, 10-, or 20-year period.

 

[phinds]

... the universe's supposed expansion?

Are you seriously questioning the expansion of the universe?

 

[hkyriazi]

Are you seriously questioning the expansion of the universe?

I suppose I am. A Doppler shift is one interpretation of the redshift/distance relationship. Others are possible. I'd be happy to see any direct confirmation of the expansion, not just one based on individual galaxy subtended angle measurements over time.

 

[phinds]

I suppose I am.

Amazing. You are seriously suggesting that all of the thousands of scientists who have confirmed it in various way have no idea what they are doing but YOU know the truth. You REALLY might want to rethink that.

 

[Vanadium 50]

Are you seriously questioning the expansion of the universe?

That's the thing you are questioning? My question for for @hkyriazi would be "Are you seriously asking if we can look at the sky today and look at it again tomorrow and tell that the galaxies are slightly smaller?"

 

[phinds]

That's the thing you are questioning? My question for for @hkyriazi would be "Are you seriously asking if we can look at the sky today and look at it again tomorrow and tell that the galaxies are slightly smaller?"

Well he did say up to 20 years

 

[PeterDonis]

I'm wondering if there is any large scale astronomical effort to assess directly the universal spatial expansion assumed by the Doppler interpretation of the redshift/distance relationship, by measuring individual galaxy subtended angles over time.

Of course there is. What you describe is called "angular size distance" or "angular diameter distance" in cosmology and is one of the primary observational parameters used to constrain possible models of the universe.

https://en.wikipedia.org/wiki/Angular_diameter_distance#Angular_size_redshift_relation

 

[PeterDonis]

The predicted decreases in size over time should be small, to be sure, but with a large enough sample size and good enough telescopes, may be measurable over a 5-, 10-, or 20-year period.

Actually, such time periods are far too short compared to the age of the universe to show measurable change in angular sizes of individual galaxies. But we can simply look at different galaxies with widely varying redshifts and widely varying distances from us, and therefore look back through a time span of billions of years.

 

[PeterDonis]

A Doppler shift is one interpretation of the redshift/distance relationship. Others are possible.

Others are logically possible, but they have been considered over decades and ruled out based on observational evidence.

 

[Bandersnatch]

The predicted decreases in size over time should be small, to be sure, but with a large enough sample size and good enough telescopes, may be measurable over a 5-, 10-, or 20-year period.

IIRC, expansion dominates observed motion of galaxies at scales >500 MPc. Let's say we want to use one such galaxy, picking one of the closest viable ones (let's say it's exactly at 500 MPc distance). The recessional velocity predicted by Hubble law should be ~35 000 km/s. Over 20-year time span, that's total receded distance of approx. $22*10^{12} km$, which is a grand total of 2 light years and change. This in turn means 1/750 000 000 change in distance and a corresponding change in the angular diameter of a diffuse object whose size is measured in arcseconds or fractions thereof.
This is not the kind of precision that's currently achievable.

I'd be happy to see any direct confirmation of the expansion

 

[Buzz Bloom]

Summary: Is there anyone examining a large sample of galaxies' subtended angles over time, as an independent test of the universe's supposed expansion?
As indicated in the title and summary, I'm wondering if there is any large scale astronomical effort to assess directly the universal spatial expansion assumed by the Doppler interpretation of the redshift/distance relationship, by measuring individual galaxy subtended angles over time.

Hi hkyriazi:

I am very surprised that no one has brought up the point I make below.

Galaxies do not expand in the manner that astronmers know that the universe expands. That is, stars in a galaxy to not move apart (due according to the phenomenon of the Hubble constant) with a speed proportional to distance. Objects in the universe that are gravitationally bound to each other do not speed away from each other proportionately to distance.

Regards,
Buzz

 

[PeterDonis]

Galaxies do not expand in the manner that astronmers know that the universe expands.

That's right, and that's why the angular size of galaxies is a useful datum--because their actual physical size can be expected to be stable.

 

[hkyriazi]

IIRC, expansion dominates observed motion of galaxies at scales >500 MPc. Let's say we want to use one such galaxy, picking one of the closest viable ones (let's say it's exactly at 500 MPc distance). The recessional velocity predicted by Hubble law should be ~35 000 km/s. Over 20-year time span, that's total receded distance of approx. $22*10^{12} km$, which is a grand total of 2 light years and change. This in turn means 1/750 000 000 change in distance and a corresponding change in the angular diameter of a diffuse object whose size is measured in arcseconds or fractions thereof.
This is not the kind of precision that's currently achievable.View attachment 246661

Thanks, Bandersnatch. Refreshing to get a calm and to-the-point response. Do you think current technology could make accurate enough measurements, and look at enough galaxies (there are, after all, quite a few of them) over that time period, to detect such tiny changes?

 

[hkyriazi]

Hi hkyriazi:

I am very surprised that no one has brought up the point I make below.

Galaxies do not expand in the manner that astronmers know that the universe expands. That is, stars in a galaxy to not move apart (due according to the phenomenon of the Hubble constant) with a speed proportional to distance. Objects in the universe that are gravitationally bound to each other do not speed away from each other proportionately to distance.

Regards,
Buzz

I'd assumed that galaxies are fairly stable in size, otherwise it'd be a confounding variable. The size change I was asking about is that due to them (galaxies not in our local cluster) being continually further away from us with time.

 

[Bandersnatch]

Do you think current technology could make accurate enough measurements, and look at enough galaxies (there are, after all, quite a few of them) over that time period, to detect such tiny changes?

I don't think so. If I'm juggling the numbers right, it's like trying to discern which object is larger - a 100 000 light-year diameter galaxy, or a 100 000.0001 light-year one, all from a distance of 150 000 000 light-years. That's a $10^{-9}$ of an arc second difference (or thereabouts). The diffraction limit on resolution of Earth-spanning radio interferometry is on the order of $10^{-6}$ arcsec.
How many galaxies you look at shouldn't matter.

 

[Vanadium 50]

it's like trying to discern which object is larger - a 100 000 light-year diameter galaxy, or a 100 000.0001 light-year one

More to the point, galaxies don't have a boundary that sharp - a part per billion. Heck, the sun doesn't have a boundary that sharp (around a meter).

 

[Vanadium 50]

Arguably, even the Earth doesn't have a boundary that sharp! (A quarter-inch)

 

[Bandersnatch]

More to the point, galaxies don't have a boundary that sharp - a part per billion. Heck, the sun doesn't have a boundary that sharp (around a meter).

I was thinking, if you had that kind of resolving power, you could pick some arbitrary features in the galaxy to serve as the boundary. Individual stars even.

 

[metastable]

I suppose I am. A Doppler shift is one interpretation of the redshift/distance relationship. Others are possible.

Others are logically possible, but they have been considered over decades and ruled out based on observational evidence.

By "others" are we referring to gravitational redshift? @PeterDonis are you saying all other logically possible interpretations have been ruled out?

https://www.physicsforums.com/threa...e-moving-away-from-a-black-hole.973395/page-2
@PeterDonis ^I will refer to the above thread in which you offered the following observation:

If the separation distance is not so small, then the ships will cover a large enough region of spacetime during the flight time of any particular photon that they cannot be treated as all being at rest in a single inertial frame during that flight time. In that case, gravitational redshift will be observable.

 

[Vanadium 50]

you could pick some arbitrary features in the galaxy to serve as the boundary. Individual stars even.

I think stars are moving 1-2 orders of magnitude too fast for that.

 

[hkyriazi]

Amazing. You are seriously suggesting that all of the thousands of scientists who have confirmed it in various way have no idea what they are doing but YOU know the truth. You REALLY might want to rethink that.

If I'm wrong, please do correct me, but from my study of the question, all the other "confirmations" are based on hypotheses that are simply *consistent* with it--for example, the baryon acoustic oscillations hypothesis to explain the CMB heterogeneity, and hot nucleosynthesis. I'm looking for direct, rather than circumstantial (interpretation-dependent), evidence of a universal expansion.

 

[hkyriazi]

How many galaxies you look at shouldn't matter.

How so? If one does a plot of, say, 1,000 galaxy subtended angles measured over time, one might expect to see a trend (significant correlation) even if individual measurements are too imprecise to say.

 

[hkyriazi]

By "others" are we referring to gravitational redshift? @PeterDonis are you saying all other logically possible interpretations have been ruled out?

FWIW, I assumed he meant Zwicky's "tired light" hypothesis, from 1929 IIRC.

 

[George Jones]

FWIW, I assumed he meant Zwicky's "tired light" hypothesis, from 1929 IIRC.

And "tired light" theories are disfavoured by observations. Gravitational time dilation in expanding universe models predicts that the rate at which photons leave a distant source is larger than the rate at which photons are received here. This leads to observable effects that are not predicted by tired light theories.

Steven Weinberg, in his 2008 grad-level book "Cosmology", writes
"For instance, one important difference between "tired light" theories and the conventional big bang theory is that in the conventional theory all rates at the source are decreased by a factor (1+z)−1, while in tired light theories there is no such slowing down. One rate that is slowed down at large redshifts in the conventional theory is the rate at which photons are emitted by the source. This is responsible for one of two factors of (1+z)−1 in ... apparent luminosity, the other factor being due to the reduction of energy of individual photons. On the other hand, if the rate of photon emission is not affected by the redshift, then in a static Euclidean universe in which photons lose energy as they travel to us, the apparent luminosity of distant source ... will be given by ... only a single factor of 1+z in the denominator.

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'. ...

In the standard big bang cosmology all rates observed from a distant source are slowed by a factor (1+z)−1, not just the rate at which photons are emitted.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 ... "

 

[Vanadium 50]

How so? If one does a plot of, say, 1,000 galaxy subtended angles measured over time, one might expect to see a trend (significant correlation) even if individual measurements are too imprecise to say.

Is that like "we lose a little on every sale but we make it up on volume?"

You need to work out the numbers rather than just spitballing it and making us refute these claims. Using Bandersnatch's numbers, which I believe are too optimistic by a factor of at least 10 and more likely 100, you need ten million galaxies to do even a 30% measurement. And this ignores the problem that galaxies don't have the sharp edge you need.

The HUDF has 0.1% of that and took 4 months to image. So you need 4000 months - about 3 centuries - to collect enough data. Then you need to do it again.

 

[Buzz Bloom]

How so? If one does a plot of, say, 1,000 galaxy subtended angles measured over time, one might expect to see a trend (significant correlation) even if individual measurements are too imprecise to say.

Hi hkyriazi:

Again I wonder why no one has made the comment I make below.

The expansion of the universe does not change any angle between observed distant objects moving away as the universe expands. The only angle changes would be with respect to non-expansion velocities of objects whose kinetic energy motion relative to comoving coordinates have a component transvese to the line of sight.

Regards,
Buzz

 

[phinds]

The expansion of the universe does not change any angle between observed distant objects moving away as the universe expands.

But no one here is talking about the angle BETWEEN objects, we're talking about the angle subtended BY the objects (from one edge to the other)

 

[PeterDonis]

By "others" are we referring to gravitational redshift?

AFAIK nobody has ever tried to explain the redshifts of distant galaxies as gravitational redshift. The reason why nobody would have ever tried is simple: it's obviously a nonstarter. For a system whose spin is slow enough (and galaxies certainly meet that criterion), any gravitational redshift larger than a fairly small amount cannot be produced by an object in a free-fall orbit. (For a non-rotating system, i.e., Schwarzschild spacetime geometry, the limit is $1 + z = \sqrt{3}$, or about $z = 0.73$.) We observe galaxies with redshifts much larger than this limit, which rules out gravitational redshift as an explanation.

are you saying all other logically possible interpretations have been ruled out?

The previous thread of yours that you linked to is not a valid reference; if you link to it again here you will receive a warning. You've had several threads now to discuss that argument and that's enough. Don't hijack someone else's thread with your personal speculation.

I will refer to the above thread in which you offered the following observation

You are quoting me out of context and claiming that what I said in that thread supports what you are trying to say here, when that is not actually the case. Do not make such a claim again or you will receive a warning and a temp ban.

 

[PeterDonis]

Gravitational time dilation in expanding universe models

I don't think "gravitational time dilation" is a good term to use here, since an expanding universe is not stationary and gravitational time dilation in the standard sense of that term is only well-defined in a stationary spacetime.

 

[Buzz Bloom]

But no one here is talking about the angle BETWEEN objects, we're talking about the angle subtended BY the objects (from one edge to the other)

Hi phinds:

I apologize. My Bad. I sort of had the idea in your post for a while, but as I read further, I became confused about what the discussion was about.

Now that I get it, I suggest it might be possible that a measurement across a combination of galaxies in relatively nearby cluster group (but not one that we are gravitationally connected with) might have a large enough angle to notice a angular shrinking over say a hundred years. I would like to research this but the three sources I was able to find quickly are somewhat daunting, and it will take me some time to try to check this out. The main problem is that I have to confirm from the data in the source that the group is far enough away to not have a significant gravitational effect on the Milky Way, and not so far away for the change in angle to be too small.

https://en.wikipedia.org/wiki/List_of_galaxy_groups_and_clusters​

https://sites.psu.edu/astrowright/ruprecht-147-the-oldest-nearby-galactic-cluster/​

http://www.atlasoftheuniverse.com/nearsc.html​

Any advise?

Regards,
Buzz