Is our region of space unique? As in there isn't much here? Credit: ESO. Edit: Ian O'Neill

The Cosmic Void: Could we be in the Middle of it?

21 Jul , 2008 by

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On large scales, the Universe is homogeneous and isotropic. This means that no matter where you are located in the cosmos, give or take the occasional nebula or galactic cluster, the night sky will appear approximately the same. Naturally there is some ‘clumpiness’ in the distribution of the stars and galaxies, but generally the density of any given location will be the same as a location hundreds of light years away. This assumption is known as the Copernican Principle. By invoking the Copernican Principle, astronomers have predicted the existence of the elusive dark energy, accelerating the galaxies away from one another, thus expanding the Universe. But say if this basic assumption is incorrect? What if our region of the Universe is unique in that we are sitting in in a location where the average density is a lot lower than other regions of space? Suddenly our observations of light from Type 1a supernovae are not anomalous and can be explained by the local void. If this were to be the case, dark energy (or any other exotic substance for that matter) wouldn’t be required to explain the nature of our Universe after all…

Dark energy is a hypothetical energy predicted to permeate through the Cosmos, causing the observed expansion of the Universe. This strange energy is believed to account for 73% of the total mass-energy (i.e. E=mc2) of the Universe. But where is the evidence for dark energy? One of the main tools when measuring the accelerated expansion of the Universe is to analyse the red-shift of a distant object with a known brightness. In a Universe filled with stars, what object generates a “standard” brightness?

NASA, ESA, and A. Field (STScI)

The progenitor of a Type Ia Supernova. Credit: NASA, ESA, and A. Field (STScI)

Type 1a supernovae are known as ‘standard candles’ for this very reason. No matter where they explode in the observable universe, they will always blow with the same amount of energy. So, in the mid-1990’s astronomers observed distant Type 1a’s a little dimmer than expected. With the basic assumption (it may be an accepted view, but it is an assumption all the same) that the Universe obeys the Copernican Principle, this dimming suggested that there was some force in the Universe causing not only an expansion, but an accelerated expansion of the Universe. This mystery force was dubbed dark energy and it is now a commonly held view that the cosmos must be filled with it to explain these observations. (There are many other factors explaining the existence of dark energy, but this is a critical factor.)

According to a new publication headed by Timothy Clifton, from the University of Oxford, UK, the controversial suggestion that the widely accepted Copernican Principle is wrong is investigated. Perhaps we do exist in a unique region of space where the average density is much lower than the rest of the Universe. The observations of distant supernovae suddenly wouldn’t require dark energy to explain the nature of the expanding Universe. No exotic substances, no modifications to gravity and no extra dimensions required.

Clifton explains conditions that could explain supernova observations are that we live in an extremely rarefied region, right near the centre, and this void could be on a scale of the same order of magnitude as the observable Universe. If this were the case, the geometry of space-time would be different, influencing the passage of light in a different way than we’d expect. What’s more, he even goes as far as saying that any given observer has a high probability of finding themselves in such a location. However, in an inflationary Universe such as ours, the likelihood of the generation of such a void is low, but should be considered nonetheless. Finding ourselves in the middle of a unique region of space would out rightly violate the Copernican Principle and would have massive implications on all facets of cosmology. Quite literally, it would be a revolution.

The Copernican Principle is an assumption that forms the bedrock of cosmology. As pointed out by Amanda Gefter at New Scientist, this assumption should be open to scrutiny. After all, good science should not be akin to religion where an assumption (or belief) becomes unquestionable. Although Clifton’s study is speculative for now, it does pose some interesting questions about our understanding of the Universe and whether we are willing to test our fundamental ideas.

Sources: arXiv:0807.1443v1 [astro-ph], New Scientist Blog


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vagueofgodalming
Member
July 22, 2008 2:20 AM
I think you have to be a bit careful with your language here. Yes, in relation to the specific issues discussed here, the Copernican principle is an assumption. However, the reason it has been adopted is because on a smaller scale, it has been borne out by the evidence, despite people initially believing the opposite. In the case of the Solar System, our local region of the galaxy, and our local region of the observable universe, it is well-supported by evidence, and not an assumption at all. I wouldn’t normally bother with this sort of criticism (you have compiled an intersting and well-written report), but I can hear the creationists sharpening their pencils to say “the science that… Read more »
Andrew James
Member
July 21, 2008 11:56 PM

Sounds more like Fred Hoyle’s “The Back Cloud” to me than any Copernican Principle.

Furthermore the assumption of the “Copernican Principle” name also smacks of “I’m right, everyone else is wrong.” – a preordained concept of correctness away from evidence or observation.

If this were the case of the solar neighbourhood, wouldn’t there be differences towards different parts of the sky and significantly larger light extinction. Frankly, I’ve been living in a void most of my life – so why is convincing?

About as relevant as “Cole’s law” – thinly sliced cabbage.

Andrew James
Member
July 21, 2008 11:57 PM

Sorry – meant to say

Frankly, I’ve been living in a void most of my life – so why is not convincing?

Andrew James
Member
July 21, 2008 11:58 PM

I’ll get it right one of these days…

Frankly, I’ve been living in a void most of my life – so why is this not convincing?

Maurice Terry
Guest
Maurice Terry
July 21, 2008 9:00 PM

In 1976 a volume of scifi short stories entitled Galactic Empires was edited by Brain Aldiss. One of the short stories was written by Michael Shaara, who later wrote the Pulitzer Prize winning Killer Angels. His short story was entitled “All the Way Back”. It was a story about how a previous evil incarnation of the human race had disappeared into a galactic void to avoid annilation. Eons later the race begins to explore space again and finds it is in a galactic void. What a strange coincidence

Andrew
Member
Andrew
July 21, 2008 9:16 PM

I suppose that if this were true, matter should gradually increase in density as we look farther and farther away.

Andrew James
Member
July 22, 2008 1:29 AM

Please Note:. The last post here alleged by “AJames” against the three was not posted by me.

I’m no idiot. I just sometimes have trouble typing these days due to my disability.

Thanks whoever did this for the moral support.

Astrofiend
Member
Astrofiend
July 21, 2008 10:41 PM
From an aesthetic point of view, I like the idea more than that of dark energy, and the fact that somebody has the sheer temerity to challenge the Copernican Principle. However: “Clifton explains conditions that could explain supernova observations are that we live in an extremely rarefied region, right near the centre…” Requiring that we be right near (basically at) the center of this special region starts ringing alarm bells for me – we’d be in a special region of a special region! If we weren’t near the middle, presumably there would be some observational evidence of this effect, like a dipole in the brightness distribution of the type 1a’s. But being in the middle, there would be… Read more »
Ethan Siegel
Guest
July 21, 2008 11:43 PM

Ian, this *could* be the case. But there was recently a study done as to whether this was the case or not, and detailed studies of large-scale structure indicate that there are no voids large enough to cause this effect within our Universe.

This is an interesting possibility that’s worth further study, but the current evidence doesn’t stand up to scrutiny.

JamesB
Guest
JamesB
July 21, 2008 11:44 PM

Ian-

Thanks for giving us dark energy ‘heretics’ some column inches!

James

PS- good article!

AJames
Guest
AJames
July 22, 2008 1:11 AM

Sorry – meant to say

Frankly, I’m an idiot. Who here needs convincing??

Stephen R. Deens
Guest
Stephen R. Deens
July 22, 2008 1:39 AM
“anthropomorphism” its a word that makes astronomers and cosmologists cringe. I happen to agree with some point of this author…its very good thinking and its htis kind of thinking we need to encourage. IMHO having Earth at the center (as the author prefers) or the fringe of the universe is NOT important…just being a part of it is enough. To be a part of the migration process. “the Universe is generally homogeneous (at any given time) and is also isotropic about any given point”…these are the words you will see in your astronmy text books. This is the #1 working assumption that is the bedrock of our past cosmology’ maybe its 100% wrong. If its worng how would… Read more »
Andy
Guest
Andy
July 22, 2008 4:48 AM

This is slightly off subject but I haven’t been able to find an answer and it’s driving me nuts. I understand, from some of the studies I’ve read, that dark matter has a temperature of 10,000C degrees and this is what prevents it from clumping together (ala ordinary matter). My question is, “How is this temperature maintained?” I mean, intergalactic space is pretty chilly. I can’t even begin to imagine how much energy would be required to heat that much mass to that temperature…and keep it there.

Aodhhan
Member
Aodhhan
July 22, 2008 5:31 AM
Mr Deens, cute but it is sided. You’re comparing apples and baseballs. Although the earth (or another body) has area of differences, it also has many similarities which you must place in your analysis. Now if you could come up with a theory showing how planets in this part of the universe are dramtically different from planets in another part of the universe… you could use that! Back to cosmic voids…. If the universe is actually expanding, much like a sponge does… eventually many voids will be created; especially given the affects of gravity on local clusters of galaxies pulling themselves slowly together. Now play the game of dark energy. Just how far and wide can it be… Read more »
Dave
Guest
Dave
July 22, 2008 6:21 AM
“Clifton explains conditions that could explain supernova observations are that we live in an extremely rarefied region, right near the centre, and this void could be on a scale of the same order of magnitude as the observable Universe.” Not only is there a “void” but by happy chance we are “right near the center”. ” . . . . he even goes as far as saying that any given observer has a high probability of finding themselves in such a location.” Huh? Am I am idiot or what. How can our little part of the cosmos be “extremely rare”, and at the same time any observer anywhere in the universe would have a “high probability of finding… Read more »
Astrofreak
Guest
Astrofreak
July 22, 2008 6:49 AM

Another fine piece of scientific BS. I have never seen an article with so many “coulds” in it!

John Mendenhall
Member
John Mendenhall
July 22, 2008 7:52 AM

True. New Scientist will probably devote an entire issue to it.

SkepticTim
Member
SkepticTim
July 22, 2008 10:17 AM
Hi Ian; Good article. I’m pleased to see alternatives to dark energy being explained in readily accessible terms. Clifton’s paper follows a long line of similar theoretical work. Perhaps one of the best advocates of alternatives is David L. Wiltshire Department of Physics & Astronomy, University of Canterbury, Christchurch, New Zealand: eg. “VIABLE INHOMOGENEOUS MODEL UNIVERSE WITHOUT DARK ENERGY FROM PRIMORDIAL INFLATION” (arXiv:gr-qc/0503099v5) where (from the beginning of his abstract) “A new model of the observed universe, using solutions to the full Einstein equations, is developed from the hypothesis that our observable universe is an underdense bubble, with an internally inhomogeneous fractal bubble distribution of bound matter systems, in a spatially flat bulk universe…” There is a quite… Read more »
RL
Member
RL
July 22, 2008 11:10 AM

Ian,

Thanks for the great article. If it has done anything, it has given me some directions and things to look up, study and, hopefully, understand and learn about more. It would be great to one day see a follow-up article that encapsulated respected cosmologists’ reaction tp and critique of Tomothy Clifton’s publication. I don’t have the knowledge or expertise to comment on its correctness, but a description of the debate would be fascinating.

Chuck Lam
Guest
Chuck Lam
July 22, 2008 7:33 PM

I have this visceral feeling that the observeable universe, that is, all we can ever see in any direction, is nothing more then a finite speck, a sphere in shape, in an unimaginable void. The “big bang” might be a simple morphing of energy in this unimaginable void into matter. And the expansion we perceive may be nothing more than the equivalent of “like polarity” repulsion” where one day we will see to the red-shift one limit and not beyond.

wpDiscuz