Is Empty Space Beyond the Universe Influencing Its Expansion?

[bogie]

Well kind of, but it's shear speculation really. We can only observe the universe directly back until t~300,000 years (when the CMB photons were last scattered). We can trace back further by using theory to match to observables such as Big Bang Nucleosynthesis matching the observed H/He ratio. This gets us to t~some fraction of a second. Early than this our theories break down.

If you want to philsophies about 'before' the big bang (which in terms of science is a sentence devoid of meaning) and a 'greater' universe beyond our own, but it is pure speculation, it cannot be tested and it doesn't make any of our current theories more or less simple.

Cosmology is a science that deals with t~smalll fraction of a second until today. Anything outside of this cannot be science since it can not be based on observations or experiment.

That is the generally accepted position and if science was limited to what we think we can prove then we have to wait until our thinking changes. Proofs can be subtle and unexpected.

It has been said that, "The discovery of dark energy was one of the biggest surprises in astronomy." But the apparent repulsive force of dark energy must be considered carefully before any monumental change is made to mainstream thinking.

Is the feeling best described as uncomfortable? Aren’t we uncomfortable that such a repulsive force could reside within the parameters of our known, visible, familiar expanding universe? Certainly it will take years of hard work to put the math together that can be accepted as mainstream.

The simple answer will have to be rejected for now. It is too much against the mainstream to consider that our known, visible, familiar expanding universe is expanding into a greater universe of lower energy density. It might seem that the only clue to the existence of such a greater universe is the acceleration itself if you are strongly ensconced in the mainstream, but if you are not so firmly ensconce there is simple logic that says that there must be a before and beyond the big bang.

If science can put any comprehensible explanation and math together to keep dark energy a repulsive force from within our familiar playing field they are committed to do that. IMHO, only as a last resort and with the greatest evaluation, study, theorizing and serious debate will science ever be able to say, "Maybe we are expanding into a greater universe."

Until then a good discussion of such a possibility is still an appropriate part of a deliberate approach to understanding dark energy. Such a discussion is appropriate because we may end up having to accept that the big bang occurred in pre-existing space from pre-existing energy.

 

[Nereid]

Yes, and I sometimes get so impatient with how slowly the wheels turn.

I find myself sitting on the edge of my chair waiting for great new findings and conclusions, and my butt is getting sore . Can’t the professionals hurry things up a bit :)?

I guess it's somewhat a matter of perspective, don't you think?

Consider that it's less than 100 years since Zwicky's paper on dark matter, Hubble's on the distance-redshift relationship, and even on http://en.wikipedia.org/wiki/The_Great_Debate" . And photographic plates were the primary tools for obtaining images (in the visual waveband) for a significant part of the working lives of many currently active professional astronomers.

The discovery of astronomical gravitational lenses (http://adsabs.harvard.edu/cgi-bin/n...mp;db_key=AST&data_type=HTML&format="?) is not yet 30 years' old!

Remember that the idea of last scattering is still theory.

A rather odd expression ... after all, isn't everything in astrophysics, beyond our solar system, "still theory"?

Granted it fits nicely. Anyway, galaxy formation in the context that you point out, i.e. the top down and the bottom up approach still is linked to what mainstream calls the surface of last scattering in one way or another.

Well, in that sense, you could also say (as Wallace pointed out) that it's also linked with current theories of gravity (GR), and of quantum mechanics ... IOW, astrophysicists bring the full range of modern physics to bear on this puzzle.

And there is still the issue of the hot beginning and where it all came from. Mainstream starts the instant after the “beginning” of the expansion. I can’t help it but to me the logic for considering the existence of a greater universe before and beyond the Big Bang is inescapable.

Indeed.

But we're doing science here, not engaging in idle speculation ...

If there is anything potentially observable that could give us a handle on "a greater universe before and beyond the Big Bang", don't you think thousands of scientists would be working on it, day and night?

If that was the case, then almost any pre-conditions would include a greater universe surrounding our expanding universe. That would change the drivers of the expansion wouldn’t it?

Who knows?

Without something quantitative, and potentially testable, your speculation is no better, or worse, than anyone else's ... or do you have a tool that no one else has thought to use yet?

This thread is about galaxy formation and movement but I should specify that I am talking about their movement relative to each other, i.e. expansion and accelerating expansion and the causes.

I think Wallace covered this well.

 

[Nereid]

That is the generally accepted position and if science was limited to what we think we can prove then we have to wait until our thinking changes. Proofs can be subtle and unexpected.

It has been said that, "The discovery of dark energy was one of the biggest surprises in astronomy." But the apparent repulsive force of dark energy must be considered carefully before any monumental change is made to mainstream thinking.

Is the feeling best described as uncomfortable? Aren’t we uncomfortable that such a repulsive force could reside within the parameters of our known, visible, familiar expanding universe? Certainly it will take years of hard work to put the math together that can be accepted as mainstream.

The simple answer will have to be rejected for now. It is too much against the mainstream to consider that our known, visible, familiar expanding universe is expanding into a greater universe of lower energy density. It might seem that the only clue to the existence of such a greater universe is the acceleration itself if you are strongly ensconced in the mainstream, but if you are not so firmly ensconce there is simple logic that says that there must be a before and beyond the big bang.

If science can put any comprehensible explanation and math together to keep dark energy a repulsive force from within our familiar playing field they are committed to do that. IMHO, only as a last resort and with the greatest evaluation, study, theorizing and serious debate will science ever be able to say, "Maybe we are expanding into a greater universe."

Until then a good discussion of such a possibility is still an appropriate part of a deliberate approach to understanding dark energy. Such a discussion is appropriate because we may end up having to accept that the big bang occurred in pre-existing space from pre-existing energy.

It may be worth your while, bogie, to invest some time in studying GR and how it applies to modern cosmology.

For example, "our known, visible, familiar expanding universe is expanding into a greater universe of lower energy density" is, I think you'll find, just a zero calorie word salad, devoid of anything useful that anyone could work on, from a scientific perspective.

Why? Well, to make sense of the various sets of good astronomical observational results, you need to use some theories. If you choose to reject those theories (GR, for example), and do not have any to put in their place, then the good astronomical observational results are essentially meaningless. And if you keep those theories (GR, for example), then the words after "is" are meaningless (or nonsense).

Although many folk no doubt wish it were otherwise, I for one can't see how cosmology can progress other than through the creation and testing of theories.

 

[bogie]

It may be worth your while, bogie, to invest some time in studying GR and how it applies to modern cosmology.

For example, "our known, visible, familiar expanding universe is expanding into a greater universe of lower energy density" is, I think you'll find, just a zero calorie word salad, devoid of anything useful that anyone could work on, from a scientific perspective.

Why? Well, to make sense of the various sets of good astronomical observational results, you need to use some theories. If you choose to reject those theories (GR, for example), and do not have any to put in their place, then the good astronomical observational results are essentially meaningless. And if you keep those theories (GR, for example), then the words after "is" are meaningless (or nonsense).

Although many folk no doubt wish it were otherwise, I for one can't see how cosmology can progress other than through the creation and testing of theories.

You do express the position of science vs. the realm of speculation. However, you did take a portion of my sentence out of context, label it, "zero calorie word salad, devoid of anything ..."

The full sentence was, "It is too much against the mainstream to consider that our known, visible, familiar expanding universe is expanding into a greater universe of lower energy density." With that you do agree from what you have said.

You did not address my comment about how subtle and unexpected proofs can be. I said that because to say that "our current understanding is that we can't know and much less prove anything beyond our event horizon" can change if the understanding of our universe changes.

You did not address the comments on dark energy, or of a discussion of dark energy including a discussion of how the existence of a greater universe might simplify the explanation of dark energy.

If you would rather that such a discussion be abandoned because it requires speculation, are you comfortable with abandoning all discussion in the scientific community that includes speculative ideas to start with?

 

[Nereid]

You do express the position of science vs. the realm of speculation. However, you did take a portion of my sentence out of context, label it, "zero calorie word salad, devoid of anything ..."

The full sentence was, "It is too much against the mainstream to consider that our known, visible, familiar expanding universe is expanding into a greater universe of lower energy density." With that you do agree from what you have said.

I've read this twice now, and must say that I don't know what it means - could you clarify please?

You did not address my comment about how subtle and unexpected proofs can be. I said that because to say that "our current understanding is that we can't know and much less prove anything beyond our event horizon" can change if the understanding of our universe changes.

Well yes, of course.

But that's not saying anything, is it?

I mean, "beyond our event horizon" implies GR (or something similar), so if a new theory replaces GR, then a new window opens up (or not; details matter).

And at any time, a new result - observational or experimental - may come along that leads to a change in our understanding of the universe.

And that change may be quite radical, or subtle, or totally boring ... but until that change, all we have is rank speculation, don't we?

You did not address the comments on dark energy, or of a discussion of dark energy including a discussion of how the existence of a greater universe might simplify the explanation of dark energy.

I thought I did ... unless you have something to replace, or extend, GR (or unless you have a much better handle on "DE"), all you've got is empty rhetoric, haven't you?

I mean, of course "the existence of a greater universe might simplify the explanation of dark energy" ... but then it might not ...

If you would rather that such a discussion be abandoned because it requires speculation, are you comfortable with abandoning all discussion in the scientific community that includes speculative ideas to start with?

Not me ... unless they've changed, discussion of overly speculative ideas is explicitly ruled out in PF's rules ...

OK, https://www.physicsforums.com/showthread.php?t=5374" (my bold):

Overly Speculative Posts:
One of the main goals of PF is to help students learn the current status of physics as practiced by the scientific community; accordingly, Physicsforums.com strives to maintain high standards of academic integrity. There are many open questions in physics, and we welcome discussion on those subjects provided the discussion remains intellectually sound. It is against our Posting Guidelines to discuss, in most of the PF forums, new or non-mainstream theories or ideas that have not been published in professional peer-reviewed journals or are not part of current professional scientific discussion. Posts deleted under this rule will be accompanied by a private message from a Staff member, with an invitation to resubmit the post in accordance with our Independent Research Guidelines. Poorly formulated personal theories, unfounded challenges of mainstream science, and overt crackpottery will not be tolerated anywhere on the site.

 

[bogie]

I've read this twice now, and must say that I don't know what it means - could you clarify please?

I was acknowledging the fact that to consider the idea of our expanding universe having a "before or beyond" was against the mainstream. I know the mention of a greater universe is the stimulus for the mainstream to defend the position that, "we cannot know and therefore it is speculation". I thought you agreed with that is all I was saying.

I thought I did ... unless you have something to replace, or extend, GR (or unless you have a much better handle on "DE"), all you've got is empty rhetoric, haven't you?

I guess that is your view and you must be pretty certain that it is the prevailing view. Otherwise you wouldn't confront a simple discussion with quotes about what the purpose of physicsforums is and what the impact of speculation can do to the education of visitors here.

I mean, of course "the existence of a greater universe might simplify the explanation of dark energy" ... but then it might not ...Not me ...

Exactly.

unless they've changed, discussion of overly speculative ideas is explicitly ruled out in PF's rules ...

OK, https://www.physicsforums.com/showthread.php?t=5374" (my bold):

"It is against our Posting Guidelines to discuss, in most of the PF forums, new or non-mainstream theories or ideas that have not been published in professional peer-reviewed journals or are not part of current professional scientific discussion."

Fine, are you saying that the current professional scientific discussion of dark energy is not going on right now? If it is not will you please explain all of the recent articles, posts, press, and yes even what actually looks like "discussion" about dark energy as a cause of the accelerating expansion?

Maybe you are saying that I can't participate yet? How do I know when I can?

 

[bogie]

...
Fine, are you saying that the current professional scientific discussion of dark energy is not going on right now? If it is not will you please explain all of the recent articles, posts, press, and yes even what actually looks like "discussion" about dark energy as a cause of the accelerating expansion?

Such a discussion is a simple step beyond current mainstream to suggest one, just one of many to be sure, explanation for the accelerating expansion; a tiny step that I have thought about for years and that unless I am mistaken, has been considered by every serious scientist since the discovery of the red shift. Dark energy makes the discussion pertinent to science if it could explain the source of dark energy.

Just empty space in the greater universe would help explain accelerating expansion. Instead of a repulsive force within our expanding universe, empty space surrounding it could pull us out into it, wouldn't it?

On the other hand “just empty” space alone would have nothing to contribute to the preconditions or the energy of the big bang. If we are going to allow the thought of space existing beyond the expanding universe, it might be appropriate to discuss that space as the source of the big bang in the first place wouldn't it?

We do know that the big bang had plenty of energy. For that reason why wouldn't we conclude that any such greater universe might contain space as well as energy that could contribute to the pre-conditions of, and initiation of the big bang?