So this is essentially another one of those areas of astronomy that completely defies falsification and cannot be tested or demonstrated scientifically. In every other area of science, if someone was trying to determine why two or more objects had moved in relationship to one another, and they claimed "space" between the objects was expanding, they would be laughed at.

The worst part of this explanation IMO, is this "force" (I use the term loosely) is powerful enough to cause galaxies to separate and accelerate, but whatever it is, it's shy around a normal science lab. What is the "cause" of this "expansion of space", and why doesn't it happen in a lab where we can test it?

That might actually be scientifically meaningful if you could actually define what it is that actually "expands" in some *physical* sense of the word (that's what "physics" is all about), but just claiming that the distance increases on it's own accord is nothing less than claiming it's "magic". The distance between objects doesn't expand in other areas of science, only in astronomy.

I'll have to read through your link when I get time today. I guess the best you can hope to provide then is a "prediction" that is based on the expansion of "space" (still an undefined term by the way) that would attempt to explain the change in distance between objects in a "better" way than non uniform acceleration. What specific observation did you have in mind?

I think this is a very good idea.

I'd also like to suggest that unless you are presenting an ATM idea MITM, this thread should be in the Q&A section.

So far I've seen no ATM ideas presented, just questions (and, perhaps, some wild statements based on a lack of understanding of the relevant aspects of modern physics?).

AS I pointed out repeatedly (among other posts, in the one you answered here!), this is simply not true. One can test this - indirectly.
Do you really not understand what I write, or do you deliberately misrepresent me?

If that other area of science involved GR, and people could describe this quantitatively based on GR, no one would laugh at all.

I already explained several times that expansion happens only on scales on which the universe is homogeneous. Why do you keep ignoring that? There is nothing bad about this - is a straightforward mathematical prediction, based on GR.

Why do you insist that something is only scientific if it can be tested in a lab? Why don't astronomical observations count as a test? Black holes, neutron stars, even our models for the interior of our own sun also can't be tested in a lab. Are all these things also unscientific, in your opinion?

What is the cause? Simple answer: essentially, we don't know. You could say that the cause was an "explosion" (at time zero) - but comparing the BB to an explosion is a rather bad analogy.


What is unphysical/magical about saying that distances increase???


sigh See above. What about starting to read what I write instead of ignoring most?


It was defined. That you don't think the definition was "physical" doesn't change the fact that a definition was provided. (Hint: all physicists seem to think that the definition is physical.)


Non-uniform acceleration of what?


As already mentioned in other posts: e. g. the results of Tolman tests and time dilation in SN brightness curves are consequences of an expansion of space. If you think you can explain these effects without an expansion of space (quantitatively, not simply by telling a nice story like "it could be that....."!), feel free to present your explanation.

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How convenient and how suspicious that all sounds if you're a skeptic like me.

In science, before one can claim that something "expands" at all, one first has to show that this thing actually expands under some kind of "controlled" laboratory conditions. You skipped that part entirely evidently. You looked at a particular observation related to moving particles in the distance and you simply "assumed" that expansion of "space" (physically undefined no less) happens, *and* you furthermore assumed that it only happens in "some" places, and only places that we cannot test. "Space" only expands when and where it wants to expand evidently.

In the real world however, the space inside an atom doesn't expand. The space between my ears doesn't expand. The space between the earth and the moon doesn't expand. The space between the sun and the earth doesn't expand. The space between stars in a galaxy doesn't expand. The space between galaxies in a cluster does not expand. Only the "space" that we can't actually test evidently does any expanding according to your theory. Talk about special pleading, ad hoc reasoning, and unfalsifiable hypothesis! Nobody can ever hope to test the idea because the ideas is completely untestable as defined. The term "space" is completely "undefined" in any physical sense, so there is nothing about your explanation that is based on "physics" in the first place, nor is it clear why it would "expand" only in some places an not everywhere.

Just so I'm clear here, is the "dark energy" that you are referring to the same thing that "causes" the expansion of space, or is the "dark energy" something else altogether?

You're obviously dancing around the head of pin here trying to ignore the basic fact that mass of the universe causes gravitational attraction that would cause the whole thing to attract and condense, not expand and separate. Why are you doing that?

Yes, but I think it's a completely meaningless analogy. In a real balloon scenario, the "stretching" is real and measurable at every level. More importantly we there is a clearly identified natural force behind the expansion of the distances between points in a balloon analogy, and there are testable aspects of physics that come into play. You've not identified the cause of the "expansion" of space, you've not defined "space" in any physically meaningful way, and in your analogy the "expansion" becomes untestable because it happens only in places we could never hope to go. In your explanation, there is no identified cause of the expansion, no force that has been used to explain the expansion, and no (lab) measurements are possible. Other than that, the analogy works great.

In a typical field of "science", we first need evidence that something can actually expand or contract *before* we can posit that concept as an "explanation" for any particular observation in the distance. You skipped a very important and critical scientific step! Instead of demonstrating that "space can expand" you just *assumed* that space (which you never defined physically) can expand and contract, but you never defined any kind of particle or field to expand or contract! It's a circular feedback loop based on metaphysics at this point, since nothing "physical" was ever defined to be able to expand or contract.

That is simply not true. That fact that you *think* it is "true" however says volumes IMO. How can we "test" this idea *outside* of the theory in question, and the observations in dispute? How do we test the idea that "space" expands in any sort of controlled, measurable, quantifiable conditions?

You seem to have a very difficult time distinguishing between a pure "observation" at a very great distance, and a "scientific test" in a true scientific sense. Can you tell me the difference between a pure observation and a scientific test?

But you never provided a falsification mechanism. You never defined any kind of "particles or fields" that might "expand". You made a metaphysical claim that sounds positively Buddhist in nature that sounds something like "The Nothingness of the universe expands". Show me how we test this idea scientifically right here on earth, or in the orbit of earth?

Expanding space is not based on GR. It's a a mythical concept unrelated to GR. GR talks in terms of "spacetime" and expanding "spacetime", but it doesn't say anything about expanding "space".

You cannot base your theory of "expanding space" on GR, because GR does not claim that "space" expands. It only speaks to "spacetime", not "space". This part of your BB theory is *not* (I repeat *not*) based on GR.

Show me otherwise.

Word salad? Excuse me? "Spacetime" is not the same as "space". GR only speaks to "spacetime", not the behaviors of "space". You're really trying hard to connect space with GR, but space is not related to GR, only spacetime.

You are talking about the cause of the distance movements of what are predominantly hydrogen suns and predominantly hydrogen plasma streams. I'm talking about the movement of objects, just like you. Like all areas of science, I chalk up that movement to a force of nature, but it has nothing to do with "expanding space" since "space" has never been shown to "expand" in any sort of controlled scientific experiment.

You can't "quantitatively" even tell me what "space" is or define how it expands so you can't do that either!

Prove it. Ultimately that's what I'm asking you to do. Acceleration is something I know can occur. "Expansion" as it has been defined thus far is "metaphysical", not "physical", since no particle or field was defined to describe "space", and there is nothing to "expand" in a pure vacuum.

What physically "expands" in this so called "space" of yours? Compare this "space" thing you've created to a "pure vacuum" (containing nothing). What is "expanding" in your definition of "space"?

Then please quantitatively explain to me what exactly is "expanding" in "space"!

If there were no other forces at work, the gravitational attraction of matter near a condensed location, would tend to cause it to "contract" rather than to expand. Something fairly energetic caused the tensor field to "expand" rather than to contract. We all agree there is is "expansion" in the spacetime tensor field. Keep that point in mind as we continue our discussion.

I have no cause to doubt that the tensor field of "spacetime" is expanding, but I have cause to doubt that the reason for that "expansion" of spacetime is due to the "expansion of space", since the term "space" is physically and energetically undefined and therefore scientifically meaningless from my skeptical perspective.

The key issue here however where we all find agreement is the notion of "energy". No doubt there is additional "energy" involved in the expansion of a such a gigantic tensor field of mass. EM fields are already known to be 39 orders of magnitude larger than gravitational tensor fields. It is the only known force of nature that I'm aware of that might still be involved in expanding the tensor fields of "spacetime". I know one thing for sure however, I do know that there is excess energy coming from somewhere, and that seems to be one place where we all agree.

Perhaps not, but the validity of GR was strictly derived from observations.

From my skeptical perspective, you've yet to qualitatively or quantitatively define how space "expands", so it is impossible to "test" anything. If I do not accept your concept on faith, you can provide no physical evidence based on any *other* area of science to show that "space" (whatever that is) actually "expands". I therefore cannot accept your premise as a "skeptic" and as a "scientist". If you could demonstrate that space expands, then it would be logical to use it as a possible explanation for the observation of an expanding tensor field. If you cannot show that "space" can expand, then it certainly cannot be considered a "force" that might expand a tensor field.

Does any of this help to better clarify my position?

A true "skeptic" considers the evidence without prejudices. You, on the other hand, keep ignoring the evidence. And even keep claiming that we can test something which in fact has already been tested extensively.


Wrong. Why should it be a requirement for any scientific idea that it can be demonstrated in a lab, under controlled conditions? In another post, I already listed several other things in astronomy for which this isn't possible.


I didn't skip it - I simply know that this is not a sensible requirement, especially for astronomy.

Wrong yet again. The BBT predicts several phenomena which wouldn't happen if space wouldn't expand (at least I've never seen a theory without space expansion explaining these phenomena; feel free to come up with one). These phenomena were observed. Conclusion: space expands.


And wrong yet again. That is not an assumption, that is a straightforward conclusion from the equations of GR.

And for the 5th time, at least: we can test it! And we did test it. And it turned out that it happens. How often do you want to ignore that?

And wrong yet again. As I explained, if space expands or not depends on the local density and (in)homogenity. Plug these factors into the equations of GR, and you get a clear answer if there is expansion or contraction. Hint: these answers match the observations. Yet another test which you conveniently ignore.

And that's in perfect agreement with what GR says. Mind you: GR does not say this because it is somehow fiddled until the desired result comes out - it does say that right from the start, if you only put the quantities mentioned above in.


For the 6th time, at least: we can test it! And we did test it. And it turned out that it happens. How often do you want to ignore that? This really becomes boring! I'll simply ignore that claim by you in the future - as long as you don't refute my argument that it can be tested, and has been tested.


If you finally began to actually read what I write, and stop ignoring the evidence, you'd see that nothing of that occurs here.


I gave a definition. If you don't like it, that does not make it unphysical.
What do you even mean with a "physical" explanation? You seem to use that term different from any physicist.

I explained that. Start actually reading what I write.


The dark energy does not cause the expansion - it causes the acceleration of the expansion. Don't you know/understand the difference?


I notice that you simply ignored these clear, simple questions.


(1) Even without a cosmological constant, a decelerated expansion is possible despite the gravitational attraction (analogy: a rocket shot away from earth - it decelerates all the time, but nevertheless keeps flying away from earth if its initial velocity was great enough).

(2) With a cosmological constant, even an accelerated expansion is possible despite the gravitational attraction, since the dark energy works counter to that attraction.

Wrong. What one usually considers is a balloon with some things (coins or something similar) glued to the surface - in the analogy, they represent galaxies or galaxy clusters. Obviously, the parts of the balloon directly below the coins do not stretch - just as the space inside galaxies / galaxy clusters does not expand! Hence the analogy makes perfect sense.


Expanding a balloon requires a force because one has to act counter to the pressure of the air surrounding it, and because its elasticity has to be overcome. In contrast, the universe isn't surrounded by anything which could counteract its expansion, and space has no elasticity which has to be overcome. Hence there is no reason why there should be a force necessary for the expansion.

If you didn't ask for a force, but merely a cause: Do you also ask for a cause when you see a rocket moving further and further away from the earth, without its engines burning?

Yes, I know that in the cause of the rocket, the initial cause was that it used its engines when lifting off from earth and reaching escape velocity. But since we have no theory for the real beginning of the universe yet, no one can say for sure what the initial cause for the expansion was. But once the expansion started, you don't need a reason for it going on!


Since we can not require the evidence beforehand in this case (as in many other cases, as you continue to ignore), what we do here is: assume that it works, calculate what observable consequences that assumption has, do the observations, and compare with the predictions. Since the observational results agree with the predictions, we conclude that the initial assumption apparently was right.

This is also a perfectly scientific method (nothing circular about that at all). If you think otherwise, please tell me why you think you are in the position to judge better than thousands of scientists what is scientific and what isn't.


Yes, it is true. I gave you a link to a page where several tests are outlined. You obviously were not aware of these tests, and so far you apparently have not looked at that page. Hence you are not in a position to judge if this is true or not.


We test the assumptions underlying a theory each time when we test the theory. Requiring an "outside" test is not necessary.




In some parts of science, observations are the only tests of a theory we can do - lab tests under controlled conditions are simply not possible. Nevertheless, that's still science. If you think otherwise, please tell me why you think you are in a better position to judge that than thousands of scientists.


I mentioned several tests, and provided a link to a page with other tests. Obviously, if the observations for these tests had come out differently than predicted, that would have falsified the expansion of space. A specific example: if space expands according to the BBT, the surface brightness of objects ("standard candles") has to decrease with (1+z)^4, where z is the redshift (that's the Tolman test). This dependance was observed, hence we have evidence that space expands. If another dependence of the surface brightness on z would have been observed, that would have falsified the idea of space expansion. etc.


Because particles or fields do not expand - space expands.


Totally, utterly wrong claims. Where on earth did you get these nonsensical ideas from?

Do you really want to claim that the BBT, with the Robertson-Walker metric (you know, the one in which spatial distances increase with time), was not derived from GR, or even that it can not be derived from GR?

GR talks about spacetime, yes, but it also can (and does!) talk about space alone! See any textbook on the BBT, where it is shown in detail how the BBT is derived from GR!



Yes, your sentence "but only if the tensor fields of spacetime expand by matter expanding." is indeed word salad. It simply makes no sense to say that a tensor field expands. This is yet another of your remarks which persuade me that you don't really know what a tensor field actually is.

I did neither mention "distance movements" nor any causes.


Hint: I am not talking about the movement of objects - I am talking about an expansion of space.


Do you want to claim that in order to explain why a motion goes on, one needs a force? If yes: ever heard of Newton's first law?


Pardon??? There is nothing to prove here - "expanding" and "accelerating" are not the same by the very definitions of the words! (am I do not mean any definitions in context with the BBT - I mean the general definitions of these words!)

For your convenience: "expanding" means that something becomes greater (i. e. its size changes with time). "accelerating" means that the velocity of something changes. Since "size changes" and "velocity changes" are obviously not the same, "expanding" and "accelerating" are obviously not the same.

Will you now admit that you made a nonsensical claim, followed by an even more nonsensical request? I doubt it. You will merely repeat your (wrong) claims that I haven't defined "space", and have not explained what is expanding.


Please explains how "physically expands" differs from simply "expands".

I already told you what "space expands" means: distances increase (on large scales etc., see above).

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Before we go any further......

Define the term "test" for me in a scientific sense. In which specific scientific "test" was it demonstrated that "space" expands?

I would have to say that there seems to be a reoccurring problem in astronomy based on the recent conversations I've been having some astronomers. Evidently some astronomers tend to confuse the concept of a consistent observation with the notion that they have already scientifically "tested" their personal explanation for the observation in question. These are not the same thing. You and I consistently "observe" the expansion of the tensor field of "spacetime". You however have not ever "tested" the "expansion of space" theory that you are now espousing as the "cause" of the expansion of the tensor field of "spacetime". Do you understand the difference?

This may be the heart of your ATM idea, MITM.

As this thread is in the ATM section, and as you are presenting an ATM idea, how about you provide all BAUT readers with your (ATM) definition of what constitutes a "test", within the scope of this forum (an astronomy, astrophysics and cosmology forum ... we'll leave the space sciences to one side for the moment).

I think before I try to decide if I am actually promoting anything that is technically "against the mainstream" here, I'd first like to understand what the "mainstream" position might be as it relates to "tests" and "science", and falsification mechanisms.

I know for instance how science is practiced in most scientific fields, and I know how I personally practice "science" as it relates to cosmology (which isn't that different). I have no idea however how every single astronomer practices the scientific method, or what might be considered "mainstream" in the areas of astronomy as opposed to any other area of science as it relates to observations, "tests", sub-hypothesis of theories and verification mechanisms of these sub-hypothesis.

I'm having a hard time here mainly because I have systematically tried to stay within the guidelines and skeptical scientific methods, and I have not disagreed with observation of the expansion of spacetime. There must be a logical scientific way to explain this ex