View Full Version : Center of the Universe
2003-Jul-26, 06:02 PM
If anyone is able, could you please answer these questions.
What do astronomers know of the very center of the universe?
Being the point of the original Big Bang, does it appear to be empty?
Do they even know exactly where it is?
And if it appears that even now it is still spewing out masses of energy that continue filling the universe, after a big Big Bang that came and went some 13 billion years ago - what is happening.
Also, considering that all that was created in the Big Bang is now still actively expanding outward – then logically, there should be a big empty space somewhere around where it originally happened.
It is easy to accept the Big Bang Theory in this expanding universe, but surely the greatest evidence of such an happening should be at the very center of the remains of that explosion. So why do we see or seem to know so little about the center of our universe.
Or am I perhaps missing something.
Please feel free to enlighten me.
2003-Jul-26, 11:54 PM
To the best of our current state of knowledge ... there is no centre of the universe. The big bang can't be thought of as a normal bomb exploding - starting somewhere and expanding out from that. The "explosion" we think of as the big bang isn't like a bomb at all .. rather an explosion of interest. An explosion OF space rather than IN it. If it were like an ordinary explosion then we should be able to look through a telescope and see the edge of the universe, but instead we look out and see back into the universe ... (see the argument about the use of language in another thread is VERY applicable here!!). Just because the universe is expanding doesn't mean it is expanding into something. Still, the universe is expanding (pretty much) uniformly and equally in every part. There is a common way to visualize this expansion without there being a universal centre.
If you take a balloon and draw a couple of points on it and then blow it up the points will, seemingly, all be moving away from each other. The three dimensional universe is to be compared with the two dimensional surface of the balloon (ie the centre of the balloon isn't part of the surface and isn't to be thought of aas the centre of the universe). This isn't to say that the universe is 2D - it;'s much more. unfortunately our brains are unable to fathom the others so lets not try. It's also important to remember that while the points on the balloon (the galaxies in thhe universe) expand the galaxies don't expand within themsleves due to them being bound by gravity.
I hope that helps. Or I might have just confused things a little more.
2003-Jul-27, 01:14 AM
It might also help (or serve to further confuse) to remember that we can only observe the universe "inside-out," i.e., the sphere of quasars that appears to surround us at distances of billions of light years from us do not form a sphere billions of light years in radius. If one could "see" the "big bang" or the "center," that "point" would necessarily be visible to us as the inside surface of a sphere billions of light years from us. To "convert" the visible universe to the "real" universe, one must turn the observed universe "inside-out." ...... from the book The Contracting Universe by John Lancas published April, 2000.
2003-Jul-27, 03:40 AM
What a fascinating question! And even more fascinating are the answers!
Am I right, therefore, in thinking that we stand on the surface of the balloon whereas the theoretical centre of the universe is in the cenre of the balloon? ie, if we're standing on the surface of the balloon, we can't actually see the centre because, well, the surface of the balloon is in the way?
Or am I just talking rubbish?? LOL :huh:
2003-Jul-27, 04:26 AM
no no ... that's the problem with the balloon analogy. The centre of the balloon is not the center of the universe. The 2D surface of the balloon is the only part that corresponds to the analogy. The 2D surface of the baloon IS the 3D universe.
2003-Jul-27, 10:11 AM
Thankyou everyone for the answers:
Yes, I have heard of the balloon theory, but I’m still confused. The main problem being that all our best observations do as you say, seem to come from the observable edges of our universe, and my kind of logic suggests that if you want to know what started the fire, examine the embers.
I will wait and see if there are a few more answers and try and get my head around this one.
2003-Jul-27, 02:53 PM
Well, I think there might be a centre. I heard about the baloon theory from this forum and I agree partially. If the Universe expands, uniform or not, then the real centre could move too leading to another centre and so on.
So there could be two disscusions about the centre of the Universe: one of the first centre and the other about the actual centre.
2003-Jul-27, 04:41 PM
Still trying to get my head around this skin of the balloon theory, so I visited the HUBBLE Site and reviewed some of their findings. (Listed below) Anything in brackets are my questions, and believe me I have plenty of them.
(I have come across the term 2d space used to explain the present state of the universe – sometimes even referred to as flat space – or the probability that if we could travel straight enough for long enough, we would end up were we started off. But if this were so then how could so much matter occupy such an apparently unwinding universe?)
January 15, 1996
Hubble's Deepest View of the Universe Unveils Bewildering Galaxies across Billions of Years
Representing a narrow "keyhole" view stretching to the visible horizon of the universe, the HDF image covers a speck of the sky only about the width of a dime located 75 feet away. Though the field is a very small sample of the heavens, it is considered representative of the typical distribution of galaxies in space because the universe, statistically, looks largely the same in all directions. Gazing into this small field, Hubble uncovered a bewildering assortment of at least 1,500 galaxies at various stages of evolution.
(In all directions – does this then include the center of the universe? If so, then perhaps this is more representative of some which is growing – not merely expanding.)
Harry Ferguson, one of the HDF team astronomers added: "One of the great legacies of the Hubble Telescope will be these deep images of the sky showing galaxies to the faintest possible limits with the greatest possible clarity from here out to the very horizon of the universe."
(This statement verifies that we, or the galaxy of which we are such a small part, is indeed far far away from the outer reaches of the galaxy. And that is the outer reaches of a galaxy as it was 11 to 12 billions of years ago. How much bigger is it now?)
Essentially a narrow, deep "core sample" of sky, the HDF is analogous to a geologic core sample of the Earth's crust. Just as a terrestrial core sample is a history of events which took place as Earth's surface evolved, the HDF image contains information about the universe at many different stages in time. Unlike a geologic sample though, it is not clear what galaxies are nearby and therefore old, and what fraction are very distant and therefore existed when the universe was newborn. "It's like looking down a long tube and seeing all the galaxies along that line of sight. They're all stacked up against one another in this picture and the challenge now is to disentangle them," said Mark Dickinson of the HDF team.
(Surely the tunnel analogy is the one thing most representative of Three Dimensional Space. To travel through our galaxy or even from our galaxy to the Andromeda Galaxy is to travel through Three Dimensional Space – therefore traveling to any destination in the universe would be the same.)
Follow-up observations will be conducted by a variety of ground and space-base telescopes at other wavelengths of the electromagnetic spectrum, from X-ray through radio. An infrared camera scheduled to be installed in Hubble during the 1997 Servicing Mission will likely image the field to search for even farther primeval galaxies, whose light has been shifted to the infrared region of the spectrum by the expansion of the universe.
(And lastly – what exactly is the universe expanding into – I have read that it is created time and space as it expands and that we may never know what lays beyond – mostly because of the vast distances involved. But whatever lays out there – cause and effect tells me our universe may just be one of many)
Damn, I’m getting an headache – I’m off to take some pills.
Perhaps if I sleep on it, it might seem a little more logical when I wake up. Some hope.
2003-Jul-27, 11:55 PM
"In the beginning was Nothing. No space, no matter or energy. But according to the quantum principle, even Nothing was unstable. Nothing began to decay; i.e. it began to "boil," with billions of tiny bubbles forming and expanding rapidly. Each bubble became an expanding universe. "
Dr. Michio Kaku (http://home.flash.net/~csmith0/bigbang.htm)
2003-Jul-28, 12:10 AM
ahh VARN! Good to see you've been reading the brilliant Kaku!
2003-Jul-28, 02:29 AM
Okay... BUT how can "nothing" do "something" like decay and boil?? :unsure:
2003-Jul-28, 07:10 AM
The balloon analogy is a good one because it implies that there is no actual centre in 4 dimensional space, which is clearly the case. The centre of space would also be the "centre of time". If you were to travel around the outside of the balloon (theoretically), you could come around to the same point. But remember the surface of the balloon is 4-dimensional so you'd have to do some time travelling as well. Weird. Confusing...all of the above.
2003-Jul-28, 12:02 PM
A little history on the ballon analogy:
In the 1920s an astronomer named alexander freidmann gave two conditions for an expanding universe:
1) The universe is the same everywhere.
2) There is no point in the universe that can be said to be the centre of the expansion of the universe.
Visualise the univesre as a 3-d expanding balloon and ourselves as 2-d. so, we are on the 2-d surface, and cant see into the 3-d space of the balloon. But there is no point on our 2-d surface tat can be said to be the centre of the expansion (the expansion starts in 3-d space). Now ,put this analogy in our universe, with us as 3-d and the universe as 4-d (with time as the fourth dimension). The expansion is ba ck in time in the 4th dimension (into which we can't see).
I hope that explains it.
2003-Jul-29, 11:52 AM
Dr. Kaku has made the assumption: 'at the beginning was
Nothing'. This cannot be proven and is a big assumption.
2003-Jul-29, 02:06 PM
[B] :) according the the known facts the sun is in the centre of the solar system we know this because of the fact all the planets revolve around it and we have over whelming evidence to prove this.We also have overwhelming evidence to prove we have a centre in our milky way galaxy.....why is it so hard to find the centre of the universe?THE SAME ANALOGY CAN BE USED TO FIND THE CENTRE OF THE UNIVERSE BY USING THE COLOUR SHIFTS OF THE GALAXIES TO SEE THE DIRECTION OF THERE MOVEMENT AND MAP OUT WHETHER THERE IS A "CENTRE OF GRAVITY' WHERE ALL KNOWN CELESTIAL OBJECTS REVOLVE AROUND. Its most likely there are multiple universes within the existing one in a much larger universe ,otherwise it would be impossible for it to hold together. Similar to your ballon theory murmured in some opinions, however imagine a clown holding a whole bunch of little helium ballons at a street corner and each ballon is a little universe and the whole bunch would consist of the whole universe. these little ballons would be most likely be interconnected by "black holes" or "worm holes" to even the "pressure between the universes to keep them "constant" similar to tornadoes that balances out differential atmospheric forces. Which ballon would be the centre of the universe, the answer would be they would all have a centre of their own universes>
2003-Jul-30, 12:51 AM
The background radiation from the big bang is the same measured from anywhere on earth if there was a center it would be more intense on one side.
2003-Aug-02, 01:08 AM
Remember that our perspective (in the middle) is an illusion.
See "The Contracting Universe" chapter on Topology of the Universe.
2003-Aug-26, 09:09 PM
My EX thought that she was the center of the Universe. Was she ever wrong. :D
2003-Aug-31, 09:47 PM
This is the point at which science and religion merge. Neither is able to come up with a good explanation about why there is something rather than nothing. They both have devised hundreds (if not thousands)of theories, but neither has any substantial proof of their theories.
From the viewpoint of science, the big bang created space. This wasn’t an explosion that expanded into space; there was no space before the big bang. That’s hard to understand, but so is a God that has always existed. God created the universe out of nothing, and the big bang created the universe out of nothing. Same-o, same-o!
If there is a center to the universe we can’t ever find it because we can’t see any of the current universe: only the universe in the past. We use the concept of a universe without a center as almost an act of faith. We can not prove that the universe has no center. There is nothing to establish the lack of center in an empirical manner.
Of course it is confusing, no one in the history of humanity has understood it. So, don’t fee bad because you don’t.
2003-Sep-01, 02:51 AM
What we are looking at here, is a physical interpretation of something which is multi-dimesional.
Who can say where is the physical center of the Universe?
And if so, by what criteria. Does one consider the space of physical center? or the center of the distribution of matter? And then again, what qualifies? Is dark matter included? or elements from other possible dimensions? And to what extent? Then the element of time. At what point of time do we want to consider?
It is becoming very interesting to consider what may have been before the big bang. Or even how it came about. Here's a hypological perspective.
What if this life form often called 'God', and sometimes dubbed a Supreame being,
is from another dimension? One that perhaps exists above and beyond our physical realm. One which we can not detect by means available to us.
And perhaps this above and beyond realm pre-existed ours by enough time for such life form(s) to develop.
Could such a being have introduced elements from his realm to create a new realm which had not existed before? Such an event may have had a violent reaction. Perhaps even a big bang.
Some long amount of time later life develops, us.
If we are part of a realm which is infearier to the realm from which it origionally came, how can we see back past our own beginning?
How can we concieve something existing and/or pre-existing us which we can not detect with our senses?
How do we contact beings from such a realm? Or do they contact us?
And if so, what criteria is set for a relationship between us and them?
Hypological of coarse.
2003-Sep-02, 03:42 PM
The present day understanding of the center of the universe is the result of the observed expansion of galaxies. Generally, the further away a galaxy is, the faster it is moving away. Every observer in every galaxy would perceive that his or her galaxy is at the center of an expanding universe. This observation is also responsible for the “big bang” model, which describes the beginning of the universe; run the clock of time in reverse and all the galaxies move back together.
The presently accepted model stops this expansion at the boundary of galaxies. Gravity is supposed to keep galaxies together, resisting the expansion of space. The balloon model referred by others previously has the galaxies represented by fixed pennies or buttons. Another example often given in college texts about the expansion, is the rising raisin bread model, with raisins representing galaxies that are being spread further apart due to the expansion of the expanding bread dough.
I have another model describing the expansion that allows galaxies and matter itself to expand. (According to the proposed theory this is a very slow expansion, 12 billion years to double in size at the current rate of expansion). Celestial and atomic stability is also preserved. The novel part of this model is that not only are galaxies the perceived center of the universe, any and every location becomes the perceived center of an expanding universe.
Was church dogma right all along?
2003-Sep-02, 09:19 PM
Where is Earth in relation to the center of the universe <_<
2003-Sep-03, 02:02 AM
It is at the center of the precieved expansion.
2003-Sep-03, 08:26 AM
:blink: [FONT=Courier][SIZE=7][COLOR=blue]Snowflake,are you saying the Earth is the center of the universe??
2003-Sep-03, 06:05 PM
I think it is important to remember something here in this discussion. A singularity cannot be defined by itself. Just as "good" cannot be defined without "evil", space cannot be defined (as we understand it) without something. In this case, let's say that nothing is the something between two or more somethings. Nothing cannot define itself. Two nothings cannot make a something, but nothing is something. We know a jar is empty because of the space defined by the jar. Yet there is nothing in the jar (with the exception of air, of course). Make any sense at all or am I kidding myself?
I don't want to pretend to understand the universe as well as the good Dr.(or even the guy that empties his trash on Wednesdays), but I agree with the guy that said follow the red-shift back to the center. Even if things have shifted a bit, we should at least be able to get a general direction to look in.
Looking toward the center, we may not see the actual center because anything that would have been there is now gone (or...?). We may be seeing the other side of the balloon. Could this account for why we are finding galaxies supposedly older than the universe? We could be mistaking the diameter for the radius. Suppose just for the sake of arguement, that we are in a city. It is ten minutes to the city center and twenty to your friend's house directly across town. Your friend is also ten minutes from the city center. Are we confusing the time it takes to get to our friends house with how long it takes him to drive home from the city center? Confusing age with distance? I wonder if there is a chance science has missed something so obvious to me.
I think of the outer fringes of the universe the in same way as the jar analogy - only this one is full of galxies 'n' stuff. The space is not only defined by the inside of the jar, but the outside too. There is something there. Otherwise the universe itself could not be defined. The idea that there is always something on the outside (you can always add 1 to the biggest number and 1 more to that and so on...) leads on to infinity. So, to answer the original question - the center of the universe (aka infinity) is where ever you want to put it because it will always be surrounded by infinity. Center is equal distance to the edges, right?
2003-Sep-03, 07:44 PM
I'm just now reading a neat book by Jenna Levin called "How the Universe Got It's Spots". She does advocate a finite universe rather than an infinite one, which is the only way in which it could have a center in the first place. Unfortunately, even if spacetime has positive curvature, there's no reason to expect it to be shaped like a simple sphere. There's a result that says that the big bang would quickly lead to chaos; and so it is actually surprising that our universe seems to be so smooth (as observed in the background radiation).
Alan Guth's inflationary theory offers one possible explanation for the smoothness; but the resulting side effect is that there may be many other areas of the universe that look totally different from our own little 'smooth' area. So I don't think it's ever going to be practical to talk about find the center of the universe. I highly recommend her book though. I'm enjoying it very much.
2003-Sep-03, 09:32 PM
To the Tripoli Kid
If the expansion of space is allowed to include matter itself. (Which is not that far fetched since matter is mostly space anyway. ) Then the center of the precieved expansion is more universal. Not only is the Earth the center of the expanding Universe, so are you and so am I.
2003-Sep-04, 09:34 AM
:rolleyes: How can we be the center of the universe if some galaxeys are blue shifted??
2003-Sep-04, 03:20 PM
There are at least two conceptual centers for the universe being discussed in this Forum. One is like the center of a pie. A physical point. The other, is the precived center due to the expansion of space.
Nomatter where one in in the universe, space is uniformly expanding away, which causes us to find ourselves at the center of an expanding universe.
I believe that our Universe is finite. We can only see so much of it. If we were to find our location relative to everything else, our galaxy most likly would not be in the center of all the other galaxies. And if there are more Universes, ours most likly would not be in the center.
So you are right to take me to task if I assert that everyone is at the center of the universe, but I think I am right to assert that everyone is at the center of the expanding universe.
2003-Sep-04, 10:16 PM
This may be a bit off the subject, but may clarify what I was trying to say earlier-
Referring back to my statement that the center of the universe (for a lack of a better term) is wherever you want to put it because it is surrounded by infinity, time should also fall into the same category. If someone asked, "What was there before time?" I would have to answer the question with another: "Well, how long before time are we talking here?". You see time is infinite too. It has no beginning and no end. The present is equally far from the beginning as the end, because they aren't really there. We are and forever will be in the middle ages.
I might add, the present is past even before you're done saying it.
2003-Sep-05, 12:52 AM
Originally posted by DippyHippy@Jul 27 2003, 03:40 AM
What a fascinating question! And even more fascinating are the answers!
Astronomers have been saying recently, that the universe is expanding at such a rate that in X billion years, if you were to look at the night sky, you wouldn't see as many stars as you can see now. Therefore, to me it seems that the universe is still expanding. This also seems to me that Astronomers (rightly or wrongly) are putting Earth OR The Milky Way, which is our Galaxy, (I'm not trying to get you to suck eggs, so please bear with me) which Earth is a part of, at the center of the Universe.
Now, it strikes me that if this analogy were true, then whatever point in the sky we were to look at, whether it be north, south, east, west, up, down, whatever, then the stars and galaxies would all be going away from us at a constant rate. Surely, to prove the point that we aren't in the center of the universe, we should be able to measure the relative distances of our local galaxies. i.e. if we were at a constant distance from, say, Andromeda, this would prove that we are travelling through space at a relative speed with all the other galaxies and therefore, NOT at the center of the universe.
The only problem that I can see from this is that we are on an outer spiral arm of the Milky Way and in (lets say) 1 million years we will have spun away from Andromeda due to the axis of the Milky Way and not from the fact that Andromeda is moving away from us because we are at the center of the universe. Therefore, the way I see it, when we arrive back to where we are now (in about 5 billion years, or however long it takes to do an orbit around the Milky Way) we will be able to see what we see now at the present time.
Don't forget, it isn't all that long ago when Astronomers thought that the Earth was at the center of the universe.
Feel free to put me right if you think that my argument is wrong.
2003-Sep-05, 04:27 AM
Everything has a begining and everything has and end.
At least that is what I think.
2003-Sep-05, 03:46 PM
Having read these posts, I love the various insights but I am still confused.
God is motioned often, yet is it possible that some supreme being could have created the universe when for all we know the universe is all there is. Those who believe in God are often given to believe that their God created the universe out of nothing. So this raises the question – what could possibly exist in nothing – the complete absence of everything? Its just as unlikely the universe was created out of nothing – energy, no matter what its source, does not work that way.
To understand more fully this God thing it would do well to understand our past, where history shows it is virtually impossible to find a previous or present civilization without religion, and those many religions of our past and present were extraordinarily diverse in their beliefs and practices. I have often asked myself what they were actually practicing, and I can only conclude that it was the same thing. All these religions its seems were created on a sense of feeling that there is perhaps something extra, some indefinable quality that exists beyond what we term as the physical world, unfortunately, like ourselves, none of our ancestors were able to fully understand it and as a consequence gave it the names and practices their imaginations dreamed up. It is human nature to give names to all we understand and that which we may never fully understand. Theory is the quest to understand the unknown, and we have given the unknown many labels in our quest to understand it.
On a world where even today there are thousands of varied religions, some very ancient; it seems improbable that if such a powerful and incredible god did create the universe and wished those he created in his own image to know he created it, that there would be such diversity in all around us.
Personally, I have a tendency to believe that what the universe represents is far far greater than those explanations given in dusty tomes. Creation is far to complex to be explained away on one page. Creation, like the birth of our universe – for me, remains an unknown mystery.
It has even been motioned that our galaxy might be near the center of the known universe, because with the exception of the local cluster of galaxies, all else in the universe seems to be moving away from us. This is not likely, because we know our solar system has been moving along with the rest of the matter in space for at least four and a half billion years, and the chances are the Milky Way Galaxy has been doing it for much longer.
So this brings us back to square one. If the universe is the result of some ancient explosion, then why is it so difficult to find its center? All other explosions in the universe have left incredible evidence of the event, so why is it that no matter where we look in space, the universe appears to be uniform? Perhaps the answer to this question can be found in inner space; in the very atoms of which we are comprised, because in many respects looking into inner space is almost like seeing a smaller picture of outer space. Atoms are like tiny solar systems where electrons revolve around a nucleus, and like fractals, this design expands outward to give us solar systems, galaxies and the universe – which chances are – if viewed from the outside would probably look just like a huge galaxy.
There is only one place on this planet, where in inner space we can find something which is expanding and uniform in all directions and that is in living, growing matter. So perhaps the next time some of us feel a need to seek God, perhaps all we have to do is to is to look out into the universe – who knows, it can’t possible be any more fantastic than those incredible magical claims made by those many religions invented by our kind. In a way we are looking from the inside out.
2003-Sep-13, 07:21 AM
According to BB theory there is no "center" (see http://www.astro.ucla.edu/~wright/nocenter.html, http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html - astrophysics, expandining universe -, and http://arcturus.mit.edu/ask/universe.html#q2). One could also say just as validly that everywhere is the center since all points are equivalent and non-unique.
2003-Sep-19, 09:18 PM
HI I am not sure you can use the balloon, because in theore the center should be in the center of the ball.The first thought is no one knows where the universe end so any supposition is only a guess.I believe if you start making guesses you create your own problem with no true answer,because no one knows.
2003-Sep-20, 12:13 AM
So, do we have to find the center to find our location in the infinity or are we on a tangent between infinities or are we here to ask the questions to enable the continuation of the infinities? Any one?
2003-Sep-20, 11:08 AM
Everything that exists in 3 dimensional space has a center, this is the nature of 3 dimensional space.
The balloon analogy is brilliant if we think only in terms of viewing our universe from outside – seeing only the outside - otherwise we have to think in terms of balloons; billions of balloons, a solid ball of balloons – each one inside another, until we reach the center – all expanding outward from that center. Otherwise we end up with billions of individual and very random points of expansion.
We know nowadays that gravity can affect light and redirect it. So do galaxies, effectively being islands of concentrated gravity in space somehow affect the properties of light over vast distances? Is the red shift nothing more than the tugging effect of gravity on light as it leaves a galaxy?
Looking out billions of light years across space only gives us clues as to what was happening billions of years ago. We would have to move billions of years into the future to know what is actually happening now. So making assumptions about what is happening now is nothing more than taking what we discover of the past and accelerating it to match an acceptable theory. Problem being; is that the universe or what we discover about it, is throwing new surprises at us constantly, surprises that constantly make us rethink what we already know. Lets hope the Vast Unknown keeps doing so – we all need mysteries of some kind.
Corkft; thanks for the email but I can’t help thinking – if we already had all the answers as you suggest – what are we doing on this forum?
Answers can only be given from already discovered knowledge; otherwise we are still seeking the answers :unsure. Our kind has done this since our brains first started functioning beyond our basic instincts. It’s taken us millions of years to discover what we now know.
Technological man is still relatively new and we have much to learn and much to discover. ;)
2003-Sep-23, 10:57 PM
A nice little read about the Big Bang - (borrowed from Scientific American)
Thought it might interest some of you.
Scientific American astronomy editor George Musser explains.
This question really has two parts. First, how was matter able to get out of the big-bang singularity? After all, physicists describe a black hole singularity as a pit into which material flows but from which it cannot escape. Let us leave aside the fact that singularities are an idealization. The basic point is that the universe was born with a tendency to expand, which overcame the tendency of matter to collapse. According to relativity theory, space does not like to remain static; for all but the most special cases, it either expands or contracts. But why it initially chose the former is still a mystery.
In some ways, you can think of the universe as a black hole turned inside-out. A black hole is a singularity into which material flows. The universe is a singularity out of which material has flowed. A black hole is surrounded by an event horizon, a surface inside which we cannot see. The universe is surrounded by a cosmological horizon, a surface outside of which we cannot see. (A crucial difference, though, is that the event horizon is fixed whereas the cosmological horizon varies from observer to observer.)
The second part of the question is: Why didn’t matter in the early universe collapse into black holes? After all, physicists say that if you squeeze matter to a high enough density, it will collapse into a black hole, and the density of matter in the early universe was extremely high. The answer is that black-hole formation actually depends on the variation in density from one place to another--and there was very little variation back then. Matter was spread out almost perfectly smoothly.
In fact, cosmologists usually turn the question around. The fact that the universe did not recollapse into a swarm of black holes is evidence that sharp density variations did not exist (or were extremely rare). This lack of sharp variations, in turn, is evidence for the inflationary model that most cosmologists today accept.
Robert J. Nemiroff, assistant professor of physics at Michigan Technological University, responds.
First of all, it is not really known whether or not the universe started from a singularity. Our measurements can take us back only so far; ideas about the nature of the cosmos at the start of the big bang are mostly unproved conjecture.
Second of all, the concept of a black hole is only one type of solution to Einstein's General Theory of Relativity, our best current theory of gravity. This reading of general relativity--known as the Schwarzschild solution--is thought to give an accurate description of the gravity near an isolated, nonrotating black hole, as well as the 'normal' gravity near the earth and throughout our solar system.
But other solutions to general relativity are known to exist, including ones that apply to a whole universe. These alternative solutions typically assume that the early universe was perfectly uniform so that there were no places for black holes to form, even if the density were so great that particles were "cheek by jowl." The most popular class of general relativity solutions applying to the entire cosmos are known as Friedmann-Robertson-Walker solutions. These formulations appear to describe correctly our expanding universe; that is, they demonstrate how objects not held together by local forces (such as the electromagnetism that bonds atoms in molecules or the gravity that keeps the earth intact) stream away from one another in a predictable manner.
Still, there is room in the theories for some of the matter in the universe to be hidden in black holes that might have formed from local, unusually dense regions in the very early universe. These black holes could conceivably contribute to the large amount of dark matter that exists in the universe. Astronomers are therefore diligently searching for these objects. In one scenario discussed by Jeremiah Ostriker of Princeton University and his collaborators, black holes as massive as one million times the mass of our sun might be common throughout the universe and still be nearly invisible. Although other black holes might come out of some big bang models involving quantum mechanics, a common expectation by cosmologists is that only elementary particles survived these early epochs of our universe.
Christ Ftaclas is an associate professor of physics, also at Michigan Tech. He adds the following:
The space-time singularity associated with the big bang differs in two important ways from the singularity associated with a black hole. First of all, a black hole has an "outside." That is, we assume that at large distances from the black hole space-time is essentially flat and defines a background against which we observe the black hole. This is not true in the case of the big bang, because we are all participants.
The second difference is critical to this question: one of the initial conditions of the big bang is expansion of the matter, whereas a Schwarzschild black hole is associated with a static gravitational field. One might think motion would not make a difference, because no velocity is great enough to escape from a black hole, but that is only true for a particle whose motion is measured relative to the stationary black hole. In the case of the big bang, everything is moving, with the result that the solution to the gravitational-field equations is fundamentally altered.
Edward L. ("Ned") Wright is the vice chair for astronomy at the University of California at Los Angeles; he also maintains a thorough on-line Cosmology Tutorial. Wright offers a somewhat different approach to this question:
A black hole is a local region from which light cannot escape. It has a boundary called the event horizon. Inside the event horizon, light cannot escape to infinity, whereas outside the event horizon, light can escape to infinity if it is traveling in the right direction. Even outside the event horizon, however, light that travels straight in toward the black hole will not escape.
In contrast, the universe is thought to be homogeneous and isotropic. Isotropic means that all directions appear the same; this property of the universe is well established by observations that show the effective temperature of the cosmic microwave background is identical in all directions to one part in 100,000. Homogeneous means that any place in the universe is equivalent to any other place. We can observe the universe from only one position, of course, but it does appear to be homogeneous on very large scales, after smoothing over the stars, galaxies, clusters of galaxies and superclusters.
A homogeneous space cannot have a boundary, so there can be no event horizon. And the future behavior of light rays cannot depend on their directions in an isotropic space. Thus, a homogeneous and isotropic universe is not a black hole. The universe does have one similarity to a black hole: light cannot escape from it. But this is true for any place in the universe and for light traveling in any direction, unlike the case for a black hole.
If this proof by contradiction seems unsatisfying, the advanced reader could look at the technical solution to the question. Solving the field equations will show that the space metric in a Friedmann-Robertson-Walker universe expands from infinite density without forming a black hole.
The universe is four-(at least)-dimensionally bound together, what we call space-time.
When we look out in space, we look back in time - towards the Big Bang. The farthest observed galaxies are the closest to the Big Bang in space-time.
Hubble's Deep Field examinations imply that galaxies at 10+ billion years are in all directions.
The Big Bang "centre" therefore appears to be an outside sphere all around us. An analogy of us being on the inside of an inside-out black hole is perhaps appropriate, with the sought after "centre" being the outside "event horizon".
If our universe came into existence at the Big Bang, then that is when matter and space-time all began.
The Big Bang explosion, as said elsewhere in this thread, was in explosion OF space, not IN space. And the centre is back along the time axis of space-time.
Further, the actual question of what there was before the Big Bang, is nonsensical, totally meaningless. Time itself started at the Big Bang. The question only comes up because we humans have such a strong sense that time is an eternal constant. We feel we move inexorably forward at a constant rate. It may well be infinite in the future, but it is not infinite in the past. And along the way, Einstein showed that it was a variable in its progression.
What there was before the Big Bang, and any God or gods as creator are subjects that are inherently unknowable. Outside the natural world - supernatural if you will. They are perfect subjects for discussion under the heading of Philosophy, where enlightenment may well be found. Here, in this forum, Ockhams razor should be wielded deftly.
2003-Sep-25, 10:49 PM
When we look out in space, we look back in time - towards the Big Bang. The farthest observed galaxies are the closest to the Big Bang in space-time.
Can’t say I agree with this Les, because when it is possible to point telescopes in ANY direction in space, only to find it is all essentially uniform – the same – surely we would first have to define the universes center (be it full of matter or still throwing matter out) before we can state which parts of the universe are most distant from that point and therefore nearest to its beginnings. That space appears to be expanding in all directions from our viewpoint only suggests that it is doing exactly the same from all and any given observable viewpoint in the universe - this is exceedingly strange for something that is still expanding from the moment it went POP. Puzzling?
Good point Hadrian.
While I realise that you initiated this interesting thread, maybe it doesn't make sense to even ask the question about the centre of the universe? :huh:
In A Brief History of Time, Hawkins talks about the "no boundary condition" of an expanding universe. If that is true, then can there be a centre? Dave Minsky referenced this a few posts back. The universe is homogeneous.
It seems to come down to us grappling with dimensions. Our brains evolved for a 3D world with time along for the ride. We think of the Big Bang as an explosion out into space. Therefore, it must have a centre. Before Einstein and Dirac (et al), we believed that the universe was a place just this simple. After they extended our language and understanding of mathematics, we know the universe is a much stranger place than most of us can get our heads around. I know I have trouble imagining 4D space - can't draw the damn thing on a graph - yet I can work with multi-(>4)-dimensional databases in executive information system applications.
I also referenced space-time, rather than just space.
Looking back to 10+ billion year old galaxies, we see them as they were back then, and at that point they must be closer to the Big Bang in space-time. Where they are in space, right now, at this instant in reality, we have no way of knowing, but, er, they should be even further away. My brain is starting to hurt.
I think I will go study Dave Minsky's links...
To get a feel for where the "center" of the universe is, it is useful to resort to analogy. Although our perceived space is three dimensional, we can visualize a two-dimensional analog of that space -- the surface of a sphere. We must imagine our entire universe as lying on the surface of that sphere, with us at a single point on that surface. When we look out into space, it is analogous to looking along the surface of that sphere.
Our universe reached its present size by expanding from a single point. In the surface-of-the-sphere analogy, the RADIUS of the sphere was smaller and smaller the further we look back in time, eventually reaching the point where the sphere suddenly appeared as a single point at the instant of the Big Bang.
So the only point that makes any sense as being the "center" of the universe is the point at the center of the sphere. IT IS NOT A POINT IN OUR UNIVERSE. There is no point at which you can point and say, "That is the center of the universe."
Our space is three-dimensional, but it still has a curvature similar to that of an ordinary sphere.
But that curvature is in a direction in which we cannot point just as a creature on the surface of the analogous two-dimensional sphere could not point toward the center of the sphere. The only directions that he could sense would be those along the surface of the sphere. Similarly, the only directions that we can sense are those in which we can point -- up, down, left, right, ahead, and behind.
We cannot point in any direction in space and say the center of the universe is in THAT direction.
The radius of our universe is so large that we have not yet been able to detect the curvature of its surface. We do now know how far we would need to travel in any given direction to find ourselves back at our starting point. However, that does not mean that the radius of the universe is infinite but only that we can see such a small sample of the surface that we cannot yet detect its curvature. The universe is vastly larger than the tiny portion of it that we can see with our telescopes. It's like trying to determine the circumference of the earth by measuring the curvature of the ground in your back yard.
2003-Sep-27, 10:57 AM
You say that our telecsopes can anly see a tiny fraction of the Universe, then why are astronomers talking about high-redshift objects (quasars) that we can see and were formed only 200.000 years after the Big Bang?
By the way I, agree that we can only see our local part of the Universe, but that's because I think the Universe is "infinite".
2003-Sep-29, 07:58 AM
There was no stable matter as such 200,000 years after the Big Bang. The period of star and galaxy formation began some 300 million years after that point. See http://www.pbs.org/deepspace/timeline/ for further information.
2003-Sep-29, 12:18 PM
Sorry, but at redshift z = 6.4 the current recordholder quasar (I think even higher redshifts will be found) has formed only 650 million years after the Big Bang. That still means we can almost see the "edge" of the Universe. And it means the time for objects to evolve is getting shoter and shorter.
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