<blockquote>
<p>I'm looking for some kind of observable evidence (that has been observed, or could be observed in the future) that could falsify one or the other theory.</p>
</blockquote>
<p>You seem to be requiring one (very high) standard for FLRW and one different one for your Antropocentric universe.  That's cheating.</p>
<p>There is no antropocentric <strong>theory</strong> to test.  We can test FLRW's theory (and GR) and have done so.  But what you are treating as an antropocentric theory is not a theory in any scientific sense.  It provides no rules or laws to make predictions from, and hence no way to make tests.</p>
<blockquote>
<p>Is there any physical evidence that can distinguish between &quot;Hubble flow&quot; and some kind of bizarre anthropocentric universe where everything just happens to have been propelled away from the Earth in a very specific way?</p>
</blockquote>
<p>By definition you are basically saying that we can construct an arbitrary scenario where everything just happens to look the way it does in terms of expansion.  It will always be possible to invent such &quot;magic&quot; circumstances if you do not have to provide a theoretical and experimental basis for them.</p>
<p>The difference is that FLRW uses GR to construct a general model that explains what we see and which can be checked and verified against observation.</p>
<p><strong>How do you define a center?</strong></p>
<p>Also note that the Antropocentric idea runs slap bang into the problem of exactly what the center of this universe is.  Is it exactly in Earth?  The Sun?  The baryocenter of the Earth-Moon system?  The (ever changing) baryocenter of the Earth-Sun-Moon system or the solar system?  Something else?  And whatever you choose <em>why</em> that choice?</p>
<p>Even if someone did not accept the motion of Earth around the Sun (etc) and claimed everything revolved around the Earth we're immediately into having no explanation for why that would be the case.</p>
<p>For me the issue of defining a center of the universe is the reason why an Anthropocentric idea makes no sense (quite apart from the complete lack of any useful theory to make predictions from).</p>

CC BY-SA 4.0
2022-02-28T12:37:19.373Z
I take the OP to be asking what set of observations are rendered coherennt (mathematically interrelated or predictable from one other) by the FLRW, which one would not expect to be coherently related if it merely happened that we were in the middle, etc.
adam.baker
CC BY-SA 4.0
2022-02-28T14:46:47.500Z
The anthropocentric theory makes some concrete predictions that are at least hypothetically testable. You could, in principle, travel to another galaxy and the expansion wouldn't look spherically symmetric. Whether you can practically test this is another matter, but it's at least in principle possible, which is more than you can say of some things called theories. There might be some practical way to test it that we haven't thought of yet (using gravitational lensing?). Saying that it doesn't make any predictions and isn't a scientific theory is an exaggeration, I'd say.
WaterMolecule
CC BY-SA 4.0
2022-02-28T14:57:58.103Z
@WaterMolecule The vagueness of the anthropocentric concept means that you can arbitrarily adapt it to match any additional observation.  That's what differentiates it from a proper scientific theory. There is no underpinning physical model (like GR) to govern what is reasonable or how to construct the theory.  That's not science, it's dogma.
StephenG - Help Ukraine
CC BY-SA 4.0
2022-03-01T01:02:20.180Z
Does GR **necessarily** negate the possibility of an Antropocentric universe? If yes, then put that in your answer.  If no, then there's your "underpinning physical model".  Also, the comments about "where do your define the center" are completely off-topic - a few AU are irrelevant over billions of light-years...
BlueRaja - Danny Pflughoeft
CC BY-SA 4.0
2022-03-01T01:31:43.260Z
@BlueRaja-DannyPflughoeft GR does not force us to construct a non-anthropocentric model, but it is extremely difficult to make an anthropocentric model with GR that matches what we actually observe (I don't know of one, but I'm no expert in GR cosmology).  The problem with the arbitrary center in the antro.. model is that it's, you know, arbitrary.  The issue of why we would be really close to the center (so a difference is "irrelevant") just brings us back to an arbitrary model with no rules defined.  No underpinning physics for the model is the problem.   FLRW does have underpinning physics.
StephenG - Help Ukraine
CC BY-SA 4.0
2022-03-01T18:47:27.330Z
This is interesting, but doesn't really answer the question - is there a physical observation you can make that distinguishes between Hubble flow and static space-time with radial motion away from Earth? I agree that the latter arrangement is a bit of a "just so" story, but that's orthogonal to whether or not it's falsifiable. It's ok if the answer is "no", I'm not planning to discard the FLRW metric in favor of geocentrism ;)
Brionius
CC BY-SA 4.0
2022-03-01T19:46:39.663Z
@Brionius You normally have to provide an *actual* theory, not just a vague idea, in order to test it.  You cannot falsify a vague idea.  FLRW provides a proper theory to test against observation.  That's the point - you want people to disprove something they cannot in any way check the detailed predicted behavior of.
StephenG - Help Ukraine
CC BY-SA 4.0
2022-03-04T14:26:23.270Z
No, you don't have to provide a theory - you have to provide a hypothesis. The anthropocentric idea *is* falsifiable.
ProfRob
CC BY-SA 4.0
2022-02-28T01:37:15.387Z
2022-12-20T08:06:09.040Z
2022-12-20T08:06:09.040Z
StephenG - Help Ukraine
<p>I think StephenG is right, but I will mention one counterfactual. Suppose we observed no galaxies more than a billion light-years away, as determined by their red shifts. Say they were roughly uniformly distributed inside that ball, but none beyond it. That would be evidence that we were at the center of the universe, at least in some sense, because somebody in one of those galaxies just about a billion light-years from us would observe something very different.</p>
<p>And it would be a big scientific mystery, because you would not expect us to be in such a unique place.</p>
<p>Instead, what we observe is exactly what you would expect if it were uniformly expanding and infinite in extent. (Although all we really know from observation is that the region containing galaxies is larger than the observable universe.)</p>

CC BY-SA 4.0
2022-02-28T19:00:33.187Z
Actually, if we saw no galaxies more than a billion light-years away, we'd most likely conclude that galaxies first formed a billion years ago...
poncho
CC BY-SA 4.0
2022-03-01T01:43:58.917Z
This is a good point, but we have many lines of evidence that stars and the earth are older than that.
Mark Foskey
CC BY-SA 4.0
2022-02-28T04:00:43.203Z
2022-02-28T04:00:43.203Z
Mark Foskey
<p>I would like to point out another flaw in the question: the model &quot;everything moves away from us proportionally to its distance&quot; is <strong>not actually anthropocentric</strong> in a basic approximation.</p>
<p>Let's disregard relativity and gravity and curvature for the moment, as the other answers address this. So imagine for simplicity a Galilean universe, euclidean and with Earth stationary at the origin, where at time <span class="math-container">$0$</span> each celestial body <span class="math-container">$B$</span> at position <span class="math-container">$p_B$</span> is currently moving directly away from the origin with constant velocity <span class="math-container">$v_B$</span> proportional to the distance, so <span class="math-container">$v_B = \alpha p_B$</span> for some constant <span class="math-container">$\alpha$</span>.</p>
<p>Now let's consider the observable information from the Earth <span class="math-container">$E$</span>. What can we observe on Earth? For every body <span class="math-container">$B$</span> we can observe the position <span class="math-container">$p_B - p_E$</span> relative to Earth, and the velocity <span class="math-container">$v_B - v_E$</span> relative to Earth, and we find that there is a proportionality relation: <span class="math-container">$v_B - v_E = v_B - 0 = \alpha p_B - 0\alpha = \alpha(p_B - p_E)$</span>. Fair enough, that's exactly what we expected. Now let's see what an alien on an alien planet <span class="math-container">$A$</span> might observe. The alien can measure the positions <span class="math-container">$p_B - p_A$</span> of celestial bodies relative to its planet, and the velocities <span class="math-container">$v_B - v_A$</span> of celestial bodies relative to its planet. Now the alien will <em>also</em> find a proportionality relation <span class="math-container">$v_B - v_A = \alpha p_B - \alpha p_A = \alpha(p_B - p_A)$</span> between these measurements for all other celestial bodies, including Earth, so the alien <em>also</em> observes everything moving directly away from its home planet, proportionally to the distance! Now the alien could claim that the alien planet <span class="math-container">$A$</span> is the special center of the universe, and it would be exactly as valid as the claim that Earth is the special center. Since both claims contradict each other, neither is true.</p>
<p>If the (simplified) model were truly anthropocentric and Earth were a cosmologically special location in the universe, the alien would be able to figure out where the special location is. But as we just saw, it isn't. It only gave the <em>impression</em> of being a special spot to you because we measure everything relative to it; it's in the middle of all our maps of space and we base our reference frame and coordinate system on it. Ancient Romans made the same mistake: they drew Rome in the center of their maps and assumed it meant Rome was the center of the world.</p>

CC BY-SA 4.0
2022-03-01T19:05:54.790Z
I think this is correct, assuming we are able to directly measure velocity. Since we are inferring velocity from redshift, do we actually obtain the same result? What I mean is, if we were to imagine a velocity field for the matter in the universe so it mimics the redshift obtained from Hubble flow, would that velocity field be proportional to position? I think the answer is yes, but I'm not sure.
Brionius
CC BY-SA 4.0
2022-03-01T21:12:16.963Z
How does this explain the CMB? It would have to come from an expanding shell, which would be anisotropic from the point of view of a distant observer.
ProfRob
CC BY-SA 4.0
2022-03-01T23:02:16.843Z
@ProfRob It doesn't. This is a really basic linear toy model of what's going on, just to highlight the fallacy in OP's "if everything moves away from us we must be the center" assumption.
Magma
CC BY-SA 4.0
2022-03-01T16:24:09.940Z
2022-12-19T10:32:58.440Z
2022-12-19T10:32:58.440Z
Magma
<p>The anthropocentric picture does not explain observations of the present <em>and distant</em> cosmic microwave background (CMB)?</p>
<p>Are we to suppose there is a large, spherical shell of optically thick gas expanding away from us faster and further away than the most distant galaxies?</p>
<p>But if so, then how could one explain the observations that demonstrate, using the inferred physical conditions of clouds of gas along sight-lines to distant quasars, that the CMB was hotter by just the right amount to be explained by cosmic expansion? i.e. That the CMB was a factor of <span class="math-container">$1+z$</span> hotter and <span class="math-container">$(1+z)^4$</span> more intense for clouds at a redshift of <span class="math-container">$z$</span> (e.g. <a href="https://www.aanda.org/articles/aa/full_html/2011/02/aa16140-10/aa16140-10.html" rel="nofollow noreferrer">Noterdaeme et al. 2010</a>).</p>
<p>The FLRW model explains this as a homogeneous, isotropic recombination event present in all the universe 13.7 billion years ago, followed by cosmological redshift and universal, adiabatic expansion.</p>
<p>In the anthropocentric idea, with a distant accelerating, emitting  spherical shell, the CMB around a distant galaxy would be highly anisotropic, since the redshift of the parts of the shell closer to the galaxy would be much smaller than in the opposite direction. Thus there would be a much higher temperature on one side of the sky. This would totally change the excitation conditions. The radiation density is proportional to <span class="math-container">$T^4$</span>, but if the two halves of the sky differed in temperature by <span class="math-container">$\pm \Delta T $</span>, the average of <span class="math-container">$(T+\Delta T)^4$</span> and <span class="math-container">$(T - \Delta T)^4$</span> is not <span class="math-container">$T^4$</span> once <span class="math-container">$\Delta T/T$</span> becomes significant, and would be much higher than in the FLRW model.</p>
<p>The temperature of the CMB has thus been <em>observed</em> to change with redshift in exactly the right way for an expanding universe, but not in accordance with an anthropocentric view.</p>

CC BY-SA 4.0
2022-07-18T08:39:28.923Z
Agreed, and there is evidence of isotropy, which convincingly refutes the anthropocentric view.
bandybabboon
CC BY-SA 4.0
2022-03-01T21:07:27.033Z
2022-07-18T08:07:44.867Z
2022-07-18T08:07:44.867Z
ProfRob
<p>I'm going to disagree with @StephenG's answer. This hypothesis is empirically falsifiable:</p>
<blockquote>
<p>for some other reason everything around us is physically moving away from us, and the farther things are moving away faster, without any expansion of space</p>
</blockquote>
<p>Redshift of light can be caused by the light source moving away from us, but it can also be caused by the expansion of space itself. Once the light has been emitted from its moving source, all redshift caused by the source's relative velocity to us has already happened, but the expansion of space continuously &quot;stretches out&quot; the light on its journey before it reaches us, redshifting it further. (General relativity also says shifting can be caused by gravity.)</p>
<p>So the expanding-space model predicts that objects can have the same relative velocity to us, but have different amounts of redshift if light from one object takes longer to reach us. The proposed anthropocentric model which claims <em>no</em> expansion of space contradicts that; if there is no expansion of space, the distance the light travels shouldn't matter, only the relative velocity of the source. (And gravity.)</p>
<p>I don't know if there is already data that would allow us to test that, but a simple way we could experimentally test it is by launching an object away from us, with a powerful laser pointing towards us. Knowing that the object is travelling at a constant velocity and that the laser produces light at a constant wavelength, the proposed anthropocentric model would predict that the laser's redshift would stay the same as it travels further away from us, whereas the expanding-space model predicts that the further it gets from us, the more its light should be redshifted.</p>

CC BY-SA 4.0
2022-03-01T19:50:03.093Z
*the proposed anthropocentric model would predict...* Except that there is **no** model to make predictions with in any detail.  The proposers of such a theory can always provide some special circumstance or adjustment to their vague idea that magics away the problem.
StephenG - Help Ukraine
CC BY-SA 4.0
2022-03-01T21:09:11.490Z
@StephenG Yes, you said so in your answer, but the proposers of *any* incorrect theory can play the "oh, but I really meant..." game just the same. You are essentially saying the hypothesis should be rejected on the basis of what you think the person proposing the hypothesis would do in response to an empirical refutation. I prefer to answer the question on the assumption that it is asked in good faith, because I do think it is reasonable to ask whether this particular kind of anthropocentrism can be empirically refuted. Your answer focuses more on whether it *needs* to be refuted.
kaya3
CC BY-SA 4.0
2022-03-01T21:36:54.537Z
I am saying that we cannot refute something scientifically without a precise definition.  In the absence of that we are just expressing vague opinions on a vague idea.  Regardless of whether of teh question is asked in good or bad faith, the concept must be properly fleshed out with enough detail to make it possible to refute or, for that matter.  You say "this particular athropocentrism" but there are no "particluars" to this question.
StephenG - Help Ukraine
CC BY-SA 4.0
2022-03-01T23:10:03.530Z
@StephenG The claim that there is no expansion of space is particular enough to be refuted.
kaya3
CC BY-SA 4.0
2022-03-01T23:27:53.767Z
It can only be refuted by making assumptions about the laws of physics being proposed to underpin the claim of no expansion.  We don't know what laws of physics are being claimed, but we don't seem to have any model that does this, supports observation *and* uses "mainstream" physical theories.  To refute this idea, we normally need to address the consequences of it's "framework" laws of physics, which, incidentally, is precisely why finding an explanation for dark matter and dark energy is proving so hard - proposed new physics tend to break other things.
StephenG - Help Ukraine
CC BY-SA 4.0
2022-03-02T10:55:26.920Z
@StephenG *"we don't seem to have any model that does this, supports observation and uses "mainstream" physical theories"* - so why not say, "yes, we can refute it, your hypothesis is contradicted by observation, assuming other mainstream physical theories"? That's what my answer says. The question is not about how to argue with someone who might reject all mainstream physical theories in stubborn pursuit of an anti-space-expansion dogma, it's about whether the hypothesis (that redshift is caused by anthropocentrism instead of space expansion) is falsifiable. I think the answer is yes.
kaya3
CC BY-SA 4.0
2022-03-02T11:59:41.910Z
Let us [continue this discussion in chat](https://chat.stackexchange.com/rooms/134521/discussion-between-stepheng-and-kaya3).
StephenG - Help Ukraine
CC BY-SA 4.0
2022-03-03T07:50:20.777Z
@StephenG I can't resist pointing out that an implication of your position is that if someone were to claim that margarine consumption drives the divorce rate in Maine, the only available reply would be, “We can't know for certain until we have a testable model of margarine consumption and the divorce rate of Maine.”
adam.baker
CC BY-SA 4.0
2022-03-03T10:29:19.983Z
@adam.baker The "margarine hypothesis" is "standalone", not comparing a new idea with an existinng established model.  It is testable by a relatively simple process of gathering statistics on well defined quantities and we're just testing *that* hypothesis.  The Anthropocentric idea has no well defined model to design a test from, and it has to do about as well as than FLRW to be considered a possible theory.  But without a detailed model to make the predictions, you cannot test it.
StephenG - Help Ukraine
CC BY-SA 4.0
2022-12-19T18:42:23.063Z
Can you actually launch an object which moves with a constant velocity away from us? It is influenced by the gravity of the earth (near the start), the sun, other stars around us, and even the whole milky way, just as the earth. (And the laser itself also has some impact.) So you'd likely have some active acceleration in that object, which makes the experiment much more difficult, and likely impossible to get enough precision to distinguish both models.
Paŭlo Ebermann
CC BY-SA 4.0
2022-03-01T12:14:48.547Z
2022-03-01T12:14:48.547Z
kaya3
<p>Consider the <a href="https://en.wikipedia.org/wiki/Cosmic_microwave_background#CMBR_dipole_anisotropy_(%E2%84%93_=_1)" rel="noreferrer">CMB Dipole anisotropy</a>.</p>
<p>You might be used to seeing the CMB like this: <a href="https://upload.wikimedia.org/wikipedia/commons/0/0b/Planck_satellite_cmb.jpg" rel="noreferrer">https://upload.wikimedia.org/wikipedia/commons/0/0b/Planck_satellite_cmb.jpg</a></p>
<p>But before it looks like that, it looks like the one in the middle of this:
<a href="https://commons.wikimedia.org/wiki/File:COBE_monopole_dipole_and_primordial_perturbations.gif" rel="noreferrer">https://commons.wikimedia.org/wiki/File:COBE_monopole_dipole_and_primordial_perturbations.gif</a></p>
<p>(After subtracting larger scale components, you get to see the smaller scale components)</p>
<p>That's because the Sun and Earth are moving relative to our local comoving frame by roughly 400 km/s, and that motion creates a redshift on one side and a blueshift on the other. Mind you, this isn't 400 km/s of spherically symmetric expansion in all directions. It's an anisotropy: 400 km/s of movement in one direction.</p>
<p>If you like, you can say, &quot;everything is relative and the Universe is moving 400 km/s relative to us.&quot; But if you follow the convention that the more massive object defines the frame (as we do when we describe our motion relative to the Earth), then clearly the Earth is moving relative to the Universe and cannot be its center.</p>

CC BY-SA 4.0
2022-03-01T10:26:34.867Z
But could we say that e.g. the Milky Way as a whole might be in the center of an expanding universe?
Paŭlo Ebermann
CC BY-SA 4.0
2022-03-01T10:39:04.390Z
@Paŭlo From https://en.wikipedia.org/wiki/Cosmic_microwave_background#CMBR_dipole_anisotropy_(%E2%84%93_=_1) From the CMB data, it is seen that the Sun appears to be moving at 368±2 km/s relative to the reference frame of the CMB [...] The Local Group — the galaxy group that includes our own Milky Way galaxy — appears to be moving at 627±22 km/s in the direction of galactic longitude ℓ = 276°±3°, b = 30°±3°
PM 2Ring
CC BY-SA 4.0
2022-03-01T09:57:39.503Z
2022-03-01T09:57:39.503Z
Alwin
<p>Here's a prediction of the FLRW theory.</p>
<p>If I stand on <em>any</em> planet <span class="math-container">$P$</span> <em>anywhere</em> in the universe, and look at <em>any</em> (sufficiently far) galaxy <span class="math-container">$G$</span> from the point of view of planet <span class="math-container">$P$</span>, and compute the distance <span class="math-container">$D$</span> between <span class="math-container">$P$</span> and <span class="math-container">$G$</span>, and compute the red-shift <span class="math-container">$R$</span> of <span class="math-container">$G$</span> from the point of view of <span class="math-container">$P$</span>, the value of <span class="math-container">$R$</span> depends on <span class="math-container">$D$</span> alone. This prediction is testable (albeit with difficulty, given that no human being has ever yet been to another planet).</p>
<p>What prediction does the &quot;anthropocentric theory&quot; make regarding the appearance of red shifts on planet <span class="math-container">$P$</span>? Does it make any prediction at all? If not, that's a definite flaw in the theory.</p>

CC BY-SA 4.0
2022-02-28T13:50:02.463Z
2022-12-19T17:48:37.713Z
2022-12-19T17:48:37.713Z
Lee Mosher
<p>I didn't read the other answers but one very simple evidence against us being a stationary center of the universe is that the CMBR redshift is not isotropic, it has a dipole anisotropy, which shows that our sun is not stationary relative to the comoving cosmic rest frame.</p>

CC BY-SA 4.0
2022-07-18T11:27:36.277Z
2022-07-18T11:27:36.277Z
matthias_buehlmann
<p>Expansion of space stretches not only single photons but whole stream of light. So similar supernovas explosions last longer in the far away galaxies.</p>
<p>Also we can use <a href="https://en.wikipedia.org/wiki/Cosmic_distance_ladder#Standard_ruler" rel="nofollow noreferrer">standard ruler</a>. If we have object of known size then expansion of space makes it seem bigger. If we confirm distance with standard candle, then we can distinguish expansion from motion.</p>
<p>E.g. elliptical galaxy with Type Ia supernovae. Sigma-D relation would allow to estimate it's actual size, and supernovae would allow to estimate distance.</p>
<p>More hypothetical way:</p>
<p>Thanks to gravitational lensing, we saw explosion of <a href="https://en.wikipedia.org/wiki/SN_Refsdal" rel="nofollow noreferrer">SN Refsdal</a> several times within a year long interval.</p>
<p>So photons that arrived last experienced +1 year of Hubble &quot;stretching&quot; or about 10^-10 difference (10^5 Hz difference for visible light). Spectral lines have width of the same order. So difference between those specters is big enough.</p>
<p><a href="https://i.sstatic.net/XkaOI.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/XkaOI.png" alt="width of spectral lines" /></a></p>
<p>But I am not sure what is the order of &quot;stretching&quot; that would be caused by random perturbations to photons during such long journey - it is possible that noise would be too big.</p>

CC BY-SA 4.0
2022-03-03T07:22:26.360Z
You are right that there is an effect (that depends on the redshift and the cosmological parameters) but wrong that it is detectable, yet.
ProfRob
CC BY-SA 4.0
2022-03-03T23:08:45.120Z
@ProbRob thank you for you well argued opinion.
Vashu
CC BY-SA 4.0
2022-03-03T05:38:39.013Z
2022-07-18T02:38:58.483Z
2022-07-18T02:38:58.483Z
Vashu
<p>If you are asking for direct physical evidence for an expansion in the sense that the distance to a given galaxy has been observed to increase, then no, there is none, simply because we have not been able to observe the universe for long enough to notice any change in distance at all, be it a global expansion or an anthropocentric one.</p>
<p>In any case, note that it is questionable to associate Hubble with the concept of an expanding universe. Hubble himself <a href="https://sites.google.com/site/bigbangcosmythology/home/edwinhubble/" rel="nofollow noreferrer">never fully believed in this</a> but assumed other physical mechanisms might be responsible for the observed redshift-distance relationship.</p>

CC BY-SA 4.0
2022-03-08T19:46:44.533Z
2022-03-08T19:53:54.397Z
2022-03-08T19:53:54.397Z
Thomas
<p>When we look in all directions, we see distant objects red-shifted, with the size of the red-shift correlated with the distance from us.</p>
<p>As I understand it, the consensus among cosmologists is that this observation is best explained by the expansion of space across intergalactic distances, a.k.a &quot;<a href="https://en.wikipedia.org/wiki/Hubble%27s_law" rel="noreferrer">Hubble flow</a>&quot;, described by the <a href="https://en.wikipedia.org/wiki/Friedmann%E2%80%93Lema%C3%AEtre%E2%80%93Robertson%E2%80%93Walker_metric" rel="noreferrer">FLRW metric</a>. This makes sense to me.</p>
<p>However, it seems that this could also be explained by the Earth being some kind of special spot in the universe, and for some other reason everything around us is physically moving away from us, and the farther things are moving away faster, without any expansion of space; with simply static space-time. To be clear, this anthropocentric theory does not seem compelling to me, and I am not advocating for it.</p>
<p>My question is this:</p>
<p>Is there any <strong>physical evidence</strong> that can distinguish between &quot;Hubble flow&quot; and some kind of bizarre anthropocentric universe where everything just happens to have been propelled away from the Earth in a very specific way?</p>
<p>I can see that the expanding space theory is simpler and more elegant, but I'm looking for some kind of observable evidence (that has been observed, or could be observed in the future) that could falsify one or the other theory.</p>
<p>Thanks!</p>

CC BY-SA 4.0
2022-02-28T09:09:17.647Z
You might be interested in https://physics.stackexchange.com/questions/676591/is-there-any-cosmological-principle, which is the same question, albeit asked in a much more technical fashion. The answer is "no", there is no way to tell.
Allure
CC BY-SA 4.0
2022-02-28T14:21:36.887Z
New non-mainstream physics theory - the rest of the universe has decided that we are dangerous and is fleeing away from us?
Jon Custer
CC BY-SA 4.0
2022-02-28T16:48:17.603Z
A more answerable question might be, given the current accuracy of our measurements of FLRW, how far away from Earth would one have to repeat the experiment for the measurement to either support or refute anthropocentrism?
Tech Inquisitor
CC BY-SA 4.0
2022-02-28T22:24:49.407Z
Really? How could it be necessary for the Earth to 'be' a special spot in the universe, or for any reason everything around us to be moving away, and farther things to be moving away faster?

More…
Robbie Goodwin
CC BY-SA 4.0
2022-03-01T19:41:57.070Z
The idea that the whole universe is purposefully running away from us is now my favorite theory!
nonDucor
CC BY-SA 4.0
2022-03-02T19:46:37.213Z
It seems to me that there are two issues here: distinguishing between an isotropic versus anisotropic universe, and distinguishing between object expanding into existing space versus space itself expanding. Your should clarify which you're asking about.
Acccumulation
CC BY-SA 4.0
2022-03-02T22:25:40.773Z
"everything around us is physically moving away from us" - this is not the case. Maybe we could say everything outside the Local Group is moving away from us. The Andromeda Galaxy is actually headed toward us.
Don Branson
CC BY-SA 4.0
2022-12-20T13:13:52.783Z
Excuse my ignorance, but haven't we also demonstrated that everything is moving away from everything, not just us? So there _is_ no assumption that it is just us
Rabbi Kaii
<cosmology><expansion><redshift><hubble-constant>
Is there physical evidence to distinguish between the expansion of space and an anthropocentric universe?
Brionius
# Is there physical evidence to distinguish between the expansion of space and an anthropocentric universe?

(Asked by: username_0 on 2022-02-28)

When we look in all directions, we see distant objects red-shifted, with the size of the red-shift correlated with the distance from us.

As I understand it, the consensus among cosmologists is that this observation is best explained by the expansion of space across intergalactic distances, a.k.a "[Hubble flow](https://en.wikipedia.org/wiki/Hubble%27s_law)", described by the [FLRW metric](https://en.wikipedia.org/wiki/Friedmann%E2%80%93Lema%C3%AEtre%E2%80%93Robertson%E2%80%93Walker_metric). This makes sense to me.

However, it seems that this could also be explained by the Earth being some kind of special spot in the universe, and for some other reason everything around us is physically moving away from us, and the farther things are moving away faster, without any expansion of space; with simply static space-time. To be clear, this anthropocentric theory does not seem compelling to me, and I am not advocating for it.

My question is this:

Is there any **physical evidence** that can distinguish between "Hubble flow" and some kind of bizarre anthropocentric universe where everything just happens to have been propelled away from the Earth in a very specific way?

I can see that the expanding space theory is simpler and more elegant, but I'm looking for some kind of observable evidence (that has been observed, or could be observed in the future) that could falsify one or the other theory.

Thanks!

**Tags:** cosmology, expansion, redshift, hubble-constant
> **Comments:**
> **username_1**: You might be interested in https://physics.stackexchange.com/questions/676591/is-there-any-cosmological-principle, which is the same question, albeit asked in a much more technical fashion. The answer is "no", there is no way to tell.  
> **username_2**: New non-mainstream physics theory - the rest of the universe has decided that we are dangerous and is fleeing away from us?  
> **username_3**: A more answerable question might be, given the current accuracy of our measurements of FLRW, how far away from Earth would one have to repeat the experiment for the measurement to either support or refute anthropocentrism?  
> **username_4**: Really? How could it be necessary for the Earth to 'be' a special spot in the universe, or for any reason everything around us to be moving away, and farther things to be moving away faster?  More…  
> **username_5**: The idea that the whole universe is purposefully running away from us is now my favorite theory!  
> **username_6**: It seems to me that there are two issues here: distinguishing between an isotropic versus anisotropic universe, and distinguishing between object expanding into existing space versus space itself expanding. Your should clarify which you're asking about.  
> **username_7**: "everything around us is physically moving away from us" - this is not the case. Maybe we could say everything outside the Local Group is moving away from us. The Andromeda Galaxy is actually headed toward us.  
> **username_8**: Excuse my ignorance, but haven't we also demonstrated that everything is moving away from everything, not just us? So there _is_ no assumption that it is just us  

---

## 10 answers

### Answer by username_9 on 2022-02-28. Score: 28

> I'm looking for some kind of observable evidence (that has been observed, or could be observed in the future) that could falsify one or the other theory.

You seem to be requiring one (very high) standard for FLRW and one different one for your Antropocentric universe. That's cheating.

There is no antropocentric **theory** to test. We can test FLRW's theory (and GR) and have done so. But what you are treating as an antropocentric theory is not a theory in any scientific sense. It provides no rules or laws to make predictions from, and hence no way to make tests.

> Is there any physical evidence that can distinguish between "Hubble flow" and some kind of bizarre anthropocentric universe where everything just happens to have been propelled away from the Earth in a very specific way?

By definition you are basically saying that we can construct an arbitrary scenario where everything just happens to look the way it does in terms of expansion. It will always be possible to invent such "magic" circumstances if you do not have to provide a theoretical and experimental basis for them.

The difference is that FLRW uses GR to construct a general model that explains what we see and which can be checked and verified against observation.

**How do you define a center?**

Also note that the Antropocentric idea runs slap bang into the problem of exactly what the center of this universe is. Is it exactly in Earth? The Sun? The baryocenter of the Earth-Moon system? The (ever changing) baryocenter of the Earth-Sun-Moon system or the solar system? Something else? And whatever you choose *why* that choice?

Even if someone did not accept the motion of Earth around the Sun (etc) and claimed everything revolved around the Earth we're immediately into having no explanation for why that would be the case.

For me the issue of defining a center of the universe is the reason why an Anthropocentric idea makes no sense (quite apart from the complete lack of any useful theory to make predictions from).

> **Comments:**
> **username_10**: I take the OP to be asking what set of observations are rendered coherennt (mathematically interrelated or predictable from one other) by the FLRW, which one would not expect to be coherently related if it merely happened that we were in the middle, etc.  
> **username_11**: The anthropocentric theory makes some concrete predictions that are at least hypothetically testable. You could, in principle, travel to another galaxy and the expansion wouldn't look spherically symmetric. Whether you can practically test this is another matter, but it's at least in principle possible, which is more than you can say of some things called theories. There might be some practical way to test it that we haven't thought of yet (using gravitational lensing?). Saying that it doesn't make any predictions and isn't a scientific theory is an exaggeration, I'd say.  
> **username_9**: @WaterMolecule The vagueness of the anthropocentric concept means that you can arbitrarily adapt it to match any additional observation.  That's what differentiates it from a proper scientific theory. There is no underpinning physical model (like GR) to govern what is reasonable or how to construct the theory.  That's not science, it's dogma.  
> **username_12**: Does GR **necessarily** negate the possibility of an Antropocentric universe? If yes, then put that in your answer.  If no, then there's your "underpinning physical model".  Also, the comments about "where do your define the center" are completely off-topic - a few AU are irrelevant over billions of light-years...  
> **username_9**: @BlueRaja-DannyPflughoeft GR does not force us to construct a non-anthropocentric model, but it is extremely difficult to make an anthropocentric model with GR that matches what we actually observe (I don't know of one, but I'm no expert in GR cosmology).  The problem with the arbitrary center in the antro.. model is that it's, you know, arbitrary.  The issue of why we would be really close to the center (so a difference is "irrelevant") just brings us back to an arbitrary model with no rules defined.  No underpinning physics for the model is the problem.   FLRW does have underpinning physics.  
> **username_0**: This is interesting, but doesn't really answer the question - is there a physical observation you can make that distinguishes between Hubble flow and static space-time with radial motion away from Earth? I agree that the latter arrangement is a bit of a "just so" story, but that's orthogonal to whether or not it's falsifiable. It's ok if the answer is "no", I'm not planning to discard the FLRW metric in favor of geocentrism ;)  
> **username_9**: @Brionius You normally have to provide an *actual* theory, not just a vague idea, in order to test it.  You cannot falsify a vague idea.  FLRW provides a proper theory to test against observation.  That's the point - you want people to disprove something they cannot in any way check the detailed predicted behavior of.  
> **username_13**: No, you don't have to provide a theory - you have to provide a hypothesis. The anthropocentric idea *is* falsifiable.  

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### Answer by username_13 on 2022-03-01. Score: 11

The anthropocentric picture does not explain observations of the present *and distant* cosmic microwave background (CMB)?

Are we to suppose there is a large, spherical shell of optically thick gas expanding away from us faster and further away than the most distant galaxies?

But if so, then how could one explain the observations that demonstrate, using the inferred physical conditions of clouds of gas along sight-lines to distant quasars, that the CMB was hotter by just the right amount to be explained by cosmic expansion? i.e. That the CMB was a factor of $1+z$ hotter and $(1+z)^4$ more intense for clouds at a redshift of $z$ (e.g. [Noterdaeme et al. 2010](https://www.aanda.org/articles/aa/full_html/2011/02/aa16140-10/aa16140-10.html)).

The FLRW model explains this as a homogeneous, isotropic recombination event present in all the universe 13.7 billion years ago, followed by cosmological redshift and universal, adiabatic expansion.

In the anthropocentric idea, with a distant accelerating, emitting spherical shell, the CMB around a distant galaxy would be highly anisotropic, since the redshift of the parts of the shell closer to the galaxy would be much smaller than in the opposite direction. Thus there would be a much higher temperature on one side of the sky. This would totally change the excitation conditions. The radiation density is proportional to $T^4$, but if the two halves of the sky differed in temperature by $\pm \Delta T $, the average of $(T+\Delta T)^4$ and $(T - \Delta T)^4$ is not $T^4$ once $\Delta T/T$ becomes significant, and would be much higher than in the FLRW model.

The temperature of the CMB has thus been *observed* to change with redshift in exactly the right way for an expanding universe, but not in accordance with an anthropocentric view.

> **Comments:**
> **username_17**: Agreed, and there is evidence of isotropy, which convincingly refutes the anthropocentric view.  

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### Answer by username_14 on 2022-02-28. Score: 10

I think StephenG is right, but I will mention one counterfactual. Suppose we observed no galaxies more than a billion light-years away, as determined by their red shifts. Say they were roughly uniformly distributed inside that ball, but none beyond it. That would be evidence that we were at the center of the universe, at least in some sense, because somebody in one of those galaxies just about a billion light-years from us would observe something very different.

And it would be a big scientific mystery, because you would not expect us to be in such a unique place.

Instead, what we observe is exactly what you would expect if it were uniformly expanding and infinite in extent. (Although all we really know from observation is that the region containing galaxies is larger than the observable universe.)

> **Comments:**
> **username_15**: Actually, if we saw no galaxies more than a billion light-years away, we'd most likely conclude that galaxies first formed a billion years ago...  
> **username_14**: This is a good point, but we have many lines of evidence that stars and the earth are older than that.  

---

### Answer by username_16 on 2022-03-01. Score: 10

I would like to point out another flaw in the question: the model "everything moves away from us proportionally to its distance" is **not actually anthropocentric** in a basic approximation.

Let's disregard relativity and gravity and curvature for the moment, as the other answers address this. So imagine for simplicity a Galilean universe, euclidean and with Earth stationary at the origin, where at time $0$ each celestial body $B$ at position $p\_B$ is currently moving directly away from the origin with constant velocity $v\_B$ proportional to the distance, so $v\_B = \alpha p\_B$ for some constant $\alpha$.

Now let's consider the observable information from the Earth $E$. What can we observe on Earth? For every body $B$ we can observe the position $p\_B - p\_E$ relative to Earth, and the velocity $v\_B - v\_E$ relative to Earth, and we find that there is a proportionality relation: $v\_B - v\_E = v\_B - 0 = \alpha p\_B - 0\alpha = \alpha(p\_B - p\_E)$. Fair enough, that's exactly what we expected. Now let's see what an alien on an alien planet $A$ might observe. The alien can measure the positions $p\_B - p\_A$ of celestial bodies relative to its planet, and the velocities $v\_B - v\_A$ of celestial bodies relative to its planet. Now the alien will *also* find a proportionality relation $v\_B - v\_A = \alpha p\_B - \alpha p\_A = \alpha(p\_B - p\_A)$ between these measurements for all other celestial bodies, including Earth, so the alien *also* observes everything moving directly away from its home planet, proportionally to the distance! Now the alien could claim that the alien planet $A$ is the special center of the universe, and it would be exactly as valid as the claim that Earth is the special center. Since both claims contradict each other, neither is true.

If the (simplified) model were truly anthropocentric and Earth were a cosmologically special location in the universe, the alien would be able to figure out where the special location is. But as we just saw, it isn't. It only gave the *impression* of being a special spot to you because we measure everything relative to it; it's in the middle of all our maps of space and we base our reference frame and coordinate system on it. Ancient Romans made the same mistake: they drew Rome in the center of their maps and assumed it meant Rome was the center of the world.

> **Comments:**
> **username_0**: I think this is correct, assuming we are able to directly measure velocity. Since we are inferring velocity from redshift, do we actually obtain the same result? What I mean is, if we were to imagine a velocity field for the matter in the universe so it mimics the redshift obtained from Hubble flow, would that velocity field be proportional to position? I think the answer is yes, but I'm not sure.  
> **username_13**: How does this explain the CMB? It would have to come from an expanding shell, which would be anisotropic from the point of view of a distant observer.  
> **username_16**: @ProfRob It doesn't. This is a really basic linear toy model of what's going on, just to highlight the fallacy in OP's "if everything moves away from us we must be the center" assumption.  

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### Answer by username_18 on 2022-03-01. Score: 7

I'm going to disagree with @StephenG's answer. This hypothesis is empirically falsifiable:

> for some other reason everything around us is physically moving away from us, and the farther things are moving away faster, without any expansion of space

Redshift of light can be caused by the light source moving away from us, but it can also be caused by the expansion of space itself. Once the light has been emitted from its moving source, all redshift caused by the source's relative velocity to us has already happened, but the expansion of space continuously "stretches out" the light on its journey before it reaches us, redshifting it further. (General relativity also says shifting can be caused by gravity.)

So the expanding-space model predicts that objects can have the same relative velocity to us, but have different amounts of redshift if light from one object takes longer to reach us. The proposed anthropocentric model which claims *no* expansion of space contradicts that; if there is no expansion of space, the distance the light travels shouldn't matter, only the relative velocity of the source. (And gravity.)

I don't know if there is already data that would allow us to test that, but a simple way we could experimentally test it is by launching an object away from us, with a powerful laser pointing towards us. Knowing that the object is travelling at a constant velocity and that the laser produces light at a constant wavelength, the proposed anthropocentric model would predict that the laser's redshift would stay the same as it travels further away from us, whereas the expanding-space model predicts that the further it gets from us, the more its light should be redshifted.

> **Comments:**
> **username_9**: *the proposed anthropocentric model would predict...* Except that there is **no** model to make predictions with in any detail.  The proposers of such a theory can always provide some special circumstance or adjustment to their vague idea that magics away the problem.  
> **username_18**: @StephenG Yes, you said so in your answer, but the proposers of *any* incorrect theory can play the "oh, but I really meant..." game just the same. You are essentially saying the hypothesis should be rejected on the basis of what you think the person proposing the hypothesis would do in response to an empirical refutation. I prefer to answer the question on the assumption that it is asked in good faith, because I do think it is reasonable to ask whether this particular kind of anthropocentrism can be empirically refuted. Your answer focuses more on whether it *needs* to be refuted.  
> **username_9**: I am saying that we cannot refute something scientifically without a precise definition.  In the absence of that we are just expressing vague opinions on a vague idea.  Regardless of whether of teh question is asked in good or bad faith, the concept must be properly fleshed out with enough detail to make it possible to refute or, for that matter.  You say "this particular athropocentrism" but there are no "particluars" to this question.  
> **username_18**: @StephenG The claim that there is no expansion of space is particular enough to be refuted.  
> **username_9**: It can only be refuted by making assumptions about the laws of physics being proposed to underpin the claim of no expansion.  We don't know what laws of physics are being claimed, but we don't seem to have any model that does this, supports observation *and* uses "mainstream" physical theories.  To refute this idea, we normally need to address the consequences of it's "framework" laws of physics, which, incidentally, is precisely why finding an explanation for dark matter and dark energy is proving so hard - proposed new physics tend to break other things.  
> **username_18**: @StephenG *"we don't seem to have any model that does this, supports observation and uses "mainstream" physical theories"* - so why not say, "yes, we can refute it, your hypothesis is contradicted by observation, assuming other mainstream physical theories"? That's what my answer says. The question is not about how to argue with someone who might reject all mainstream physical theories in stubborn pursuit of an anti-space-expansion dogma, it's about whether the hypothesis (that redshift is caused by anthropocentrism instead of space expansion) is falsifiable. I think the answer is yes.  
> **username_9**: Let us [continue this discussion in chat](https://chat.stackexchange.com/rooms/134521/discussion-between-stepheng-and-kaya3).  
> **username_10**: @StephenG I can't resist pointing out that an implication of your position is that if someone were to claim that margarine consumption drives the divorce rate in Maine, the only available reply would be, “We can't know for certain until we have a testable model of margarine consumption and the divorce rate of Maine.”  
> **username_9**: @adam.baker The "margarine hypothesis" is "standalone", not comparing a new idea with an existinng established model.  It is testable by a relatively simple process of gathering statistics on well defined quantities and we're just testing *that* hypothesis.  The Anthropocentric idea has no well defined model to design a test from, and it has to do about as well as than FLRW to be considered a possible theory.  But without a detailed model to make the predictions, you cannot test it.  
> **username_19**: Can you actually launch an object which moves with a constant velocity away from us? It is influenced by the gravity of the earth (near the start), the sun, other stars around us, and even the whole milky way, just as the earth. (And the laser itself also has some impact.) So you'd likely have some active acceleration in that object, which makes the experiment much more difficult, and likely impossible to get enough precision to distinguish both models.  

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### Answer by username_20 on 2022-03-01. Score: 5

Consider the [CMB Dipole anisotropy](https://en.wikipedia.org/wiki/Cosmic_microwave_background#CMBR_dipole_anisotropy_(%E2%84%93_=_1)).

You might be used to seeing the CMB like this: <https://upload.wikimedia.org/wikipedia/commons/0/0b/Planck_satellite_cmb.jpg>

But before it looks like that, it looks like the one in the middle of this:
<https://commons.wikimedia.org/wiki/File:COBE_monopole_dipole_and_primordial_perturbations.gif>

(After subtracting larger scale components, you get to see the smaller scale components)

That's because the Sun and Earth are moving relative to our local comoving frame by roughly 400 km/s, and that motion creates a redshift on one side and a blueshift on the other. Mind you, this isn't 400 km/s of spherically symmetric expansion in all directions. It's an anisotropy: 400 km/s of movement in one direction.

If you like, you can say, "everything is relative and the Universe is moving 400 km/s relative to us." But if you follow the convention that the more massive object defines the frame (as we do when we describe our motion relative to the Earth), then clearly the Earth is moving relative to the Universe and cannot be its center.

> **Comments:**
> **username_19**: But could we say that e.g. the Milky Way as a whole might be in the center of an expanding universe?  
> **username_21**: @Paŭlo From https://en.wikipedia.org/wiki/Cosmic_microwave_background#CMBR_dipole_anisotropy_(%E2%84%93_=_1) From the CMB data, it is seen that the Sun appears to be moving at 368±2 km/s relative to the reference frame of the CMB [...] The Local Group — the galaxy group that includes our own Milky Way galaxy — appears to be moving at 627±22 km/s in the direction of galactic longitude ℓ = 276°±3°, b = 30°±3°  

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### Answer by username_22 on 2022-02-28. Score: 2

Here's a prediction of the FLRW theory.

If I stand on *any* planet $P$ *anywhere* in the universe, and look at *any* (sufficiently far) galaxy $G$ from the point of view of planet $P$, and compute the distance $D$ between $P$ and $G$, and compute the red-shift $R$ of $G$ from the point of view of $P$, the value of $R$ depends on $D$ alone. This prediction is testable (albeit with difficulty, given that no human being has ever yet been to another planet).

What prediction does the "anthropocentric theory" make regarding the appearance of red shifts on planet $P$? Does it make any prediction at all? If not, that's a definite flaw in the theory.


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### Answer by username_23 on 2022-07-18. Score: 1

I didn't read the other answers but one very simple evidence against us being a stationary center of the universe is that the CMBR redshift is not isotropic, it has a dipole anisotropy, which shows that our sun is not stationary relative to the comoving cosmic rest frame.


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### Answer by username_24 on 2022-03-03. Score: 1

Expansion of space stretches not only single photons but whole stream of light. So similar supernovas explosions last longer in the far away galaxies.

Also we can use [standard ruler](https://en.wikipedia.org/wiki/Cosmic_distance_ladder#Standard_ruler). If we have object of known size then expansion of space makes it seem bigger. If we confirm distance with standard candle, then we can distinguish expansion from motion.

E.g. elliptical galaxy with Type Ia supernovae. Sigma-D relation would allow to estimate it's actual size, and supernovae would allow to estimate distance.

More hypothetical way:

Thanks to gravitational lensing, we saw explosion of [SN Refsdal](https://en.wikipedia.org/wiki/SN_Refsdal) several times within a year long interval.

So photons that arrived last experienced +1 year of Hubble "stretching" or about 10^-10 difference (10^5 Hz difference for visible light). Spectral lines have width of the same order. So difference between those specters is big enough.

[![width of spectral lines](https://i.sstatic.net/XkaOI.png)](https://i.sstatic.net/XkaOI.png)

But I am not sure what is the order of "stretching" that would be caused by random perturbations to photons during such long journey - it is possible that noise would be too big.

> **Comments:**
> **username_13**: You are right that there is an effect (that depends on the redshift and the cosmological parameters) but wrong that it is detectable, yet.  
> **username_24**: @ProbRob thank you for you well argued opinion.  

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### Answer by username_25 on 2022-03-08. Score: -2

If you are asking for direct physical evidence for an expansion in the sense that the distance to a given galaxy has been observed to increase, then no, there is none, simply because we have not been able to observe the universe for long enough to notice any change in distance at all, be it a global expansion or an anthropocentric one.

In any case, note that it is questionable to associate Hubble with the concept of an expanding universe. Hubble himself [never fully believed in this](https://sites.google.com/site/bigbangcosmythology/home/edwinhubble/) but assumed other physical mechanisms might be responsible for the observed redshift-distance relationship.


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