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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?
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
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 says the earth is old is all supported by an *assumption*. Why do you always *assume* that things are uniform?” and so on. We don’t. Observable evidence led us to this point.
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.
Sorry – meant to say
Frankly, I’ve been living in a void most of my life – so why is not convincing?
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?
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
I suppose that if this were true, matter should gradually increase in density as we look farther and farther away.
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.
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 no such effect, so we couldn’t observe it… Hmmm.
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.
Ian-
Thanks for giving us dark energy ‘heretics’ some column inches!
James
PS- good article!
Sorry – meant to say
Frankly, I’m an idiot. Who here needs convincing??
“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 one expect it to manifest itself?
we see “PRECIDENTS” like this all over this planet and we are ignoring it in outer space..
mother nature has shown us that nothing is homogenous and nothing is ever isotropic…its unhealthy for the body of the planet to be homogenous….matter and resources must be kept moving or its growth is stagnated.
One part of Earth has more oil, another better more nutrient Nitrogen rich soil, another better water quality, more inhabitable land etc..ect etc…man, animals and plants all migrate and its healthier that way for a total biosphere.
I’m willing ot bet its the same in instellar space among all the galaxies….and its very likely that its more condensed in “pockets”
the only argument is are these pockets near us or the oppositre side of the universe? But is NOT evenly distributed..Nature is telling us that every day on this Earth.
on earth the natural rsources are spread out unevely and because of this distinction plants, animals and birds all must migrate toward greener pastures.or die due to inactvity and insufficient energy consumption..and as the density of these materials are changed the rate and direction of the migration must follows. The herd follows the greener grass and the predators folow the herd.
its the same perhaps between regions of space and between galaxies and as such we should be challening this belive in homogenous and istropy in how the universe is distributed.
its far from even
go check out the word “anthropomorphism”:
also if things are NOT so homogenous we not only have a problme using type 1a supernova as “standard candles” but we also have to re-consider proto-planetary formation and how the instellar dust and hydrogen atoms were distributed when a protostar is forming.
Its probably not as even this mix of gas and heavy elements…But what are the local triggers that could lead to this?
ask this:
If things are not so homogenous and isotropic how could that effect the bitht of a Joavian gas giant near a star that is similar to our sun in magnitude?
Could this be why these big Giants we are finding are so close to their suns (i.e Venus distance) and so much bigger than Jupiter?
everything is uneven, poorly distruted and is in a total universe wide migration in its attempt to restore order to the chaos of big bang. The same thing is happoenbing on Earth–everyhthing is re-distrubuting
maybe Big Bang wasn’t so isotropic afterall and things are slowly migrating to correct this?
dark matter seems like its got too much faith in Homogenous isotropic universes.
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.
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 stretched? Is there a limit; and if so, what happens at this limit or will it leave voids as well… only to be found clinging near galaxies whose gravity is pulling it nearer?
“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 themselves in such a location”? Do we have another Shroedinger’s Cat here or something? Are we both uniquely rare and overwhelmingly common at the same time, but by observing we quantumly effect our entire region of the universe?
Another fine piece of scientific BS. I have never seen an article with so many “coulds” in it!
True. New Scientist will probably devote an entire issue to it.
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 significant body of research on this and other alternatives to dark energy. A few papers that I have found quite interesting include:
Mustapha Ishak, James Richardson, Delilah Whittington, David Garred “Dark Energy or Apparent Acceleration Due to a Relativistic Cosmological Model More Complex than FLRW?” (arXiv:0708.2943v1 [astro-ph]) where their abstract begins “We use the Szekeres inhomogeneous relativistic models in order to fit supernova combined data sets. We show that with a choice of the spatial curvature function that is guided by current observations, the models fit the supernova data as well as the LCDM model without requiring any dark energy component….”
“Light-cone averages in a swiss-cheese universe” (arXiv:0710.5505v2 [astro-ph] ) by Valerio Marra and Edward W. Kolb: where their abstract concludes “…That is, the equation of state depends linearly on the distance the photon travels through voids. We conclude that within our toy model, the holes must have a present size of about 250 Mpc to be able to mimic the concordance model.”
“Is dark energy an effect of averaging?” by Nan Li, Marina Seikel and Dominik J. Schwarz (arXiv:0801.3420v1 [astro-ph])
where they explain “The present standard model of cosmology states that the known particles carry only a tiny fraction of total mass and energy of the Universe. Rather, unknown dark matter and dark energy are the dominant contributions to the cosmic energy budget. We review the logic that leads to the postulated dark energy and present an alternative point of view, in which the puzzle may be solved by properly taking into account the influence of cosmic structures on global observables. We illustrate the effect of averaging on the measurement of the Hubble constant.”
And the review by Subir Sarkar (Gen Relativ Gravit (2008) 40:269–284, DOI 10.1007/s10714-007-0547-7, RESEARCH ARTICLE) “Is the evidence for dark energy secure?” where he reviews a number of alternatives and concludes in part “… Such alternatives may seem contrived but this must be weighed against our lack of any fundamental understanding of the inferred tiny energy scale of the dark energy. It may well be an artifact of an oversimplified cosmological model, rather than having physical reality.”
I sometimes think that far too much attention is given to dark energy when it is only one hypothesis amongst many that can explain a few of the many problems remaining in our understanding of cosmology.
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.
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.
i’ve got no background whatsoever in physics to back this idea up, but sometimes when i read about the universe being more like strands and filliments than a big ball shaped object it occurs to me if the universe expands like a bunch of wild weeds in all directions, curvations, etc, then wouldn’t a lot of aspects of the Copernican model get debunked?
do we really even have a sense of how big the universe is to presume that the nature of gravity and the electromagnetic forces is uniform?
hope my questions make sense. i’ve got a limited vocab with this stuff.
A gran escala, el universo es homogéneo e isotrópico, lo que significa que sin importar el lugar donde uno esté ubicado, y más allá de nebulosas y cúmulos galácticos ocasionales, el cielo nocturno parecerá aproximadamente el mismo. Naturalmente hay ciertas “agrupaciones” en la distribución de las estrellas y galaxias, pero por lo general la densidad de cualquier lugar será igual a la de cualquier otra ubicación a cientos de años-luz. […] Fuentes: Ian O’Neill para Universe Today, arXiv:0807.1443v1 [astro-ph], New Scientist Blog.
What New Scientist is to science equates to what super market tabloids are to science. I don’t mind alternative theories, but anything from NS leaves me suspicious.
My thanks to Sceptic Tim for the arXiv eprint references. Lots of reading for the next few days. Also, might Type Ia SN ‘standard candles’ not be so standard after all? It seems that under or over luminous examples of these SN are being found with increasing regularity. If this is so, where does this leave Dark Energy & cosmic acceleration?
Robb,
Think of the universe (just after the big bang) as a compacted sponge. Pick your shape… square, cube, circular, rectangular, pony shape etc.
As time goes by, the sponge expands. No matter where you are located inside this sponge everything is moving away from you; current theory suggests this… with the exception of objects which are gravitationally affected by one another; such as local groups of galaxies.
With this being the case, then certainly voids are created over time.
Take into account that about every 5 years or so, we seem to find out we are misjudging distances somewhat, and the universe is a different age than we previously thought.
Every time we find technology to see something new or better we do come up with new answers, however we come up with a lot more questions!
Of course, remember that the “Big Bang” hypothesis is also called into question by the same things that bring concepts like dark energy into question. “Dark Energy” is invoked to try to explain some of the persistent holes in the “Big Bang” hypothesis, so where there is no need for “Dark Energy” there may also no longer be a need for the “Big Bang”. So don’t continue to try and shoehorn the “Big Bang” into a reasonable picture of the state of our universe if it no longer makes sense.
I also want to point out that a LOT of money gets spent on research that is popular. So even when the research tends to demonstrate that the assumptions of the theory or hypothesis are wrong, don’t expect the researchers to embrace the facts. It’s hard to pay your mortgage and send your kids to college when your career is in a discredited scientific field (something we are seeing now in the AGW field).
I may be missing the point, but surely, isn’t this part of what Science is about: refining models, ideas & theories, checking assumptions & seeing wether the assumptions can hold true/be supported by evidence/observations when scaled up, down or generally pushed to extremes?
I must agree with alphonso that Science is all about refining models, ideas & theories. While the original theory of the Big Bang may not fit well with current theories of quantum cosmology, it’s certainly no reason to dump the theory as a whole. Just look at inflation, multidimensional string theory, spontaneous inflation, multiverse theory developed not to disprove the Big Bang theory but to expand on it’s framework to help explain and-or match observations made in the past several years. Remember, even Einstein spent his last years trying to bring a mathematical explanation of gravity into general relativity, whereupon he eventually failed. Now quantum theory is undergoing the same problem trying to develop a quantum theory of gravity, to incorporate it into a framework with quantum mechanical explanations of the electromagnetic , weak (electroweak) & strong forces. Surely an inspiring & worthwhile pursuit. Anyway, great article Ian & quite thought provoking.
“After all, good science should not be akin to religion where an assumption (or belief) becomes unquestionable.”
Now, go and try to question “climate change…”
thanks Aodhhan. appreciate your thoughts. i find this stuff fascinating.
seems like the big bang will be hard to dethrone on the whole, not that it needs toppling. how else to account for the expansion of matter in all directions if not some ‘bang’ at the start, whether or not it was from a singularity or some branes clanging together.
it continues to astound me how some of the ideas/forces that underlie the universe are so simple (like gravity) while others are so complex and strange (like quantum particle behavior).
one way or the other though the universe exists for the propagation of life. whereever life is able to exist, it does. it gets wiped out in massive waves, then starts again. at least until all the stars go out. or maybe we can slide out through another dimension. ok i’m rambling now.
But doesn’t the fitting of the CMB require dark energy? How does that look if that isn’t included then?
Of course we’re in a void. It’s only prudent to quarantine a virus somewhere it can’t harm anyone.
robbb-
Part of the problem with the “Big Bang” is that is it trying to explain why everything is traveling out-wards. Except that much of the recent work is starting to show that it may not be. The only real “evidence” of an expanding universe is the “standard candle” supernovas that aren’t really standard and the red-shift of galaxies.
The first one is like trying to measure the size of the universe in cubits – there is no standard length of a cubit, it changed depending on who you were talking too. And it was measured in terms of things that had no standard lengths themselves (the Romans measured the cubit as the measure from a man’s hip to the fingers of the outstretched opposite arm).
The second one is the real problem. While ‘tired light’ has been discounted, it’s not the only hypothesis on why the red shift might occur. Given a recent experiment where light was slowed down to 38MPH (yes – MILES PER HOUR) in a laboratory under conditions similar to deep space, how can we say that light traveling 8 billion lightyears won’t be affected in ways that create a blue or red shift?
I don’t buy the ‘big bang’ theory as is, and I believe most don’t; there are too many internal theories about what the universe was just before it.
I can’t totally buy in to the universe as a whole expanding from the ‘big bang’; however it is hard to dismiss what the doppler affect is displaying. To me, I still wonder why in the large scheme of things it looks like the universe is stretching out, however at a (relatively) smaller scale we don’t see galaxies, dark matter, galaxy clusters etc stretching out equally. I don’t think gravity alone can keep the small things in check the way things currently are.
It’s good to be critical and not believe everything you hear. You don’t have to totally dismiss something, but if your gut tells you something isn’t right… then you should seek out an answer. Sooner or later, it will get proven; even if it takes a millenia.
thanks JamesB and Aodhhan. yet more food for thought. let’s say for the sake of argument that the Big Bang theory is wrong. what’s your feeling on how the universe actually formed?
Brilliant! Sometimes the simple explanation can be the correct explanation. Maybe dark energy will go the way of the luminous aether. (Remember Michelson-Moreley experiment?)
robbb-
Recently I’ve been looking at alternative theories of cosmology and physics and am leaning towards a infinite universe that has always existed and will always exist. One that is not expanding, though there is a horizon beyond which we will never be able to see or know anything about, ever.
The 3 dimensional universe is bounded by a 4th dimension that isn’t infinite. And while it’s useful sometimes to think of “time” as a “one way dimension” it’s actually isn’t a dimension at all, so the 4 dimensions are all spacial dimensions and are the only dimensions that exist.
Matter and energy is the intrusion of this finite 4th dimension into the 3 dimensions we know and forces are part of how these intrusions are played out in 3d space (which is a very simplified concept, but gets the point across). Under this model, Quantum Mechanics and General Relativity actually dovetail with each other, rather than conflict as under current dogma – they are simply unified as part of the same phenomenon.
The biggest difference mathematically is the concept that “null” is a real value and represents a value that is as real as any other value and has meaning (IE- nothing is something too…).
I’ve posted on this site before that I think the next big breakthru in physics and cosmology will be “dimensional physics”, just like the last big breakthru was “electromagnetic physics” and before that was “kinetic physics”. Einstein touched on this concept in General Relativity, with the idea that gravity was simply warped space.
The infamous Michelson-Moreley experiment was a failure due to applying kinetic physics to an electromagnetic physics problem. I firmly believe that we are applying electromagnetic physics to a dimensional physics problem, and the aether of the Michelson-Moreley experiment is the dark energy of today, and neither exist except in our misunderstanding of the nature of the universe.
You may have guess that I favor a particular alternate theory, and I do. It’s the only one I found incorporates what I call “dimensional physics” into it’s solutions.
Regarding the suitability of using Type Ia SN as standard candles, this link arXiv:astro-ph/0701912v2 addresses the possibility of SN light-curve evolution over large (z>1.5) cosmological distances. It does point out the suitability of using corrected SN Type Ia lightcurves to infer the existence of Dark Energy but also notes that higher accuracy lightcurve corrections will be needed to distinguish between different cosmological models of Dark Energy, especially at higher redshifts.
thanks JamesB. I don’t have enough understanding of the science to have a strong opinion on your concept, but it’s interesting b/c I havent read much dissent about the Big Bang and pondering alternatives is always fun brain gymnastics.
I won’t go too far down this road at the moment but I have had some extremely unusual, detailed experiences with what one might call the supernatural, which either means I am nuts (doesnt feel like it) or there is much more to be discovered about the true nature of existence. I feel it’s not all Out There. Much of it is Right Here.
One thing I feel I have learned is that an openness to new knowledge and a humility before the great mysteries is somehow the key to incredible discoveries and leaps of mind. I am open to all possibilities.
To: JamesB., I share your suspicion that the universe is infinite, always was and always will be. It is also possible that we are at the center of what we regard as the “observable universe” is nothing more than a finite spherical volumn of perhaps 25 to 35 billion light years in diameter. Assuming the current “red-shift” theory is a good one and linear; man or any intelligence will never see beyond their “red-shift one” barrier. As to what is beyond this barrier? It is probably the same stuff we currently see in all directions. There is nothing logical to suggest otherwise.
O this I am sure its true,
The Universe is just a clue.
yepper
Where’s the category for aliens?
😉