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apolloman
2008-Sep-15, 01:54 PM
This may well be silly question but I can’t figure it out (I’m not the brightest person).

The premise I understand to be true is:

a) the Universe was infinitely small and had infinite energy “just prior” to the BB
b) just after the BB, the Universe inflated (as per the BB inflation theory) at a colossal rate and then calmed down to a more tranquil inflation process

The question then is if the universe was infinitely small, how did it get to the size we see today ?

I thought that anything either infinitely small or large (or with any infinite parameter) will not change no matter what you do it precisely because of this infinite characteristic.
Example, halve a infinite group of atoms and you still have an infinite group of atoms.

What am I missing here ?

The same applies for the energy at the singularity of a black hole. I understand that at the singularity, energy becomes infinite. But considering that the amount of energy entering a black hole or producing a black hole is not infinite, where does this energy come from ?

Lepton
2008-Sep-15, 02:13 PM
This may well be silly question but I can’t figure it out (I’m not the brightest person).

The premise I understand to be true is:

a) the Universe was infinitely small and had infinite energy “just prior” to the BB
b) just after the BB, the Universe inflated (as per the BB inflation theory) at a colossal rate and then calmed down to a more tranquil inflation process

The question then is if the universe was infinitely small, how did it get to the size we see today ?

I thought that anything either infinitely small or large (or with any infinite parameter) will not change no matter what you do it precisely because of this infinite characteristic.
Example, halve a infinite group of atoms and you still have an infinite group of atoms.

What am I missing here ?

The same applies for the energy at the singularity of a black hole. I understand that at the singularity, energy becomes infinite. But considering that the amount of energy entering a black hole or producing a black hole is not infinite, where does this energy come from ?

You have singularity defined incorrectly. A singularity is a mathematical construct and it is a place where mathematics fails. Look at a singularity as a point of infinite curvature of space-time and not as an incorrect point of no volume and all the "infinite density" nonsense disappears.

apolloman
2008-Sep-15, 02:24 PM
Is this valid also for the Big Bang ?

Lepton
2008-Sep-15, 02:26 PM
Is this valid also for the Big Bang ?

Depends. If the big bang started from a singularity...yes.

apolloman
2008-Sep-15, 02:35 PM
Lepton: sorry to insist but how could the universe at its beginning be a point of infinite curvature of space-time if the latter were created at the same time ?
I might be beating around the bush but I'd like to at least try to understands this.

Lepton
2008-Sep-15, 02:41 PM
Lepton: sorry to insist but how could the universe at its beginning be a point of infinite curvature of space-time if the latter were created at the same time ?
I might be beating around the bush but I'd like to at least try to understands this.

Reread my first post and read it carefully. Then explain why you are attributing something to me I didn't say.

ETA - Then again maybe the BB wasn't from a singularity.

Lepton
2008-Sep-15, 02:48 PM
Lepton: sorry to insist but how could the universe at its beginning be a point of infinite curvature of space-time if the latter were created at the same time ?
I might be beating around the bush but I'd like to at least try to understands this.

Space-time was created?

apolloman
2008-Sep-15, 02:50 PM
Lepton: i didn't mean to attribute you something erroneous... I simply missed the point of your statement. Like I said, i'm not the brightest..

so if the BB was from a singularity, then it came from a point of infinite curvature of space-time ? Have I understood this correctly ?

If it wasn't, then the infinite business doesn't hold ? Correct ?

I don't want to waste your time, maybe you can suggest some reading to do ?
Thanks

apolloman
2008-Sep-15, 02:52 PM
Space-time was created?
This is my layman's understanding... I thought that at the moment of BB, space and time were essentially brought existence... I've got this wrong too ?:doh:

Lepton
2008-Sep-15, 02:54 PM
Lepton: i didn't mean to attribute you something erroneous... I simply missed the point of your statement. Like I said, i'm not the brightest..

so if the BB was from a singularity, then it came from a point of infinite curvature of space-time ? Have I understood this correctly ?

If it wasn't, then the infinite business doesn't hold ? Correct ?

I don't want to waste your time, maybe you can suggest some reading to do ?
Thanks

As I said reread my original post to see how I said singularities are defined so you can stop attributing my "illustration" as the definition I gave.

Lepton
2008-Sep-15, 02:56 PM
This is my layman's understanding... I thought that at the moment of BB, space and time were essentially brought existence... I've got this wrong too ?:doh:

No. You have a simplification of the BB. Let me ask you a question, what was the BB an expansion of?

apolloman
2008-Sep-15, 03:02 PM
lepton: BB was the creation and expansion of space and time(space-time) and the "distribution" of energy within them (it).
By creation I mean that before the BB, there was no space or time (no space-time) to talk of.

Lepton
2008-Sep-15, 03:06 PM
lepton: BB was the creation and expansion of space and time(space-time) and the "distribution" of energy within them (it).
By creation I mean that before the BB, there was no space or time (no space-time) to talk of.

If the BB was the expansion of space-time doesn't that give you any type of hint that space-time was contained in (or was) whatever the object was that the BB came from? Saying there was no space-time prior to the BB is correct in the sense that the BB was the beginning of time but that in no way says anything prior to the BB.

Cougar
2008-Sep-15, 03:06 PM
The premise I understand to be true is:
a) the Universe was infinitely small and had infinite energy “just prior” to the BB

No. Essentially, we don't know what the heck was going on at the time of the "big bang." What we know is that in the universe's past, the ambient temperature was hotter, and everything was closer together. When we "run the movie backwards" all the way to the "beginning," our extrapolations fail. As Harvard GR prof. Tony Rothman said:



"We mentioned that the FLRW cosmology begins with a singularity. This is a much more serious breakdown than a flat tire or a cracked engine block. It is, in fact, a physical impossibility -- a region where the laws of physics break down altogether and even spacetime comes to an end."

mugaliens
2008-Sep-15, 03:54 PM
Lepton: sorry to insist but how could the universe at its beginning be a point of infinite curvature of space-time if the latter were created at the same time ?
I might be beating around the bush but I'd like to at least try to understands this.

Easy. The snake swallowed it's own tail, and kept swallowing, until it was infinately curved in upon itself.

Then, something happened. It retched. And the universe was born.

Neverfly
2008-Sep-15, 04:17 PM
What does the number one look like?
In arabic, it's : 1
But in Numerals it's : I.
In the ST Universe, number 1 looks like :
http://i.somethingawful.com/mjolnir/images/elpintogrande~13-riker.jpg

The number 1 is just a mathematical construct. It doesn't "look" like anything.
Same with singularity. You are trying to treat it as something you can look at.
You can't.

Jeff Root
2008-Sep-15, 06:34 PM
Hello, apolloman!



The premise I understand to be true is:

a) the Universe was infinitely small and had infinite energy “just prior”
to the BB

As Cougar, said, we don't know how the whole thing got started.
What we do is extrapolate backward in time, applying the laws of
physics to try to understand what the conditions must have been.
That extrapolation tells us that the farther back we look, the denser
and hotter the Universe was. At some moment, the extrapolation
tells us, the Universe would have been infinitely dense. That would
be "time zero" of the Big Bang.

I don't think the Universe was ever infinitely dense. I think that
whatever caused the Big Bang was happening instead.

However, the proportions of abundance of the nuclear isotopes of
hydrogen, deuterium, helium, and lithium suggest very strongly that
the density, temperature, and pressure must have been within a
quite narrow range of values during the first few minutes, so even
if we don't know what the conditions were at time zero, we can be
pretty sure what they were a minute or so later.

The size of the Universe is completely unknown, except that it must
be considerably larger than what we can see. It is conceivable that
it is infinite.

It is also possible that the Universe involved in the Big Bang is only
part of a larger Universe. In that case, the part involved in the Big
Bang is finite, but the larger Universe could be either finite or infinite.

I personally don't think that an infinite Universe could all be involved
in a single Big Bang. That makes no sense to me. However, the
conventional wisdom is that if the Universe is infinite, then it has
been infinite from the beginning. That implies that if the matter which
we see spreading out is infinite in extent, then it was already infinite
in extent in the first instant of the Big Bang.

Which is to say, if the Universe is infinite, it was never small.

If the Universe is not infinite, then we just don't how big it was at the
very beginning.

The energy of the Universe wasn't infinite, either, but energy is a
relative measure. By taking gravitational potential energy as negative,
the overall energy of the Universe can be considered to be zero.



The same applies for the energy at the singularity of a black hole.
I understand that at the singularity, energy becomes infinite. But
considering that the amount of energy entering a black hole or producing
a black hole is not infinite, where does this energy come from ?
The energy in or of a black hole is not infinite.

The density of the matter which forms a black hole tends toward
infinite as it collapses. So the matter at the center approaches
infinite density. That density produces a curvature of spacetime
which also approaches infinite.

Any black hole has a particular mass. The greater the mass, the
larger the size of the black hole. As you undoubtedly know, mass
is a form of energy. So the mass of a black hole has a particular
energy equivalent, found by the familiar E=mc^2 formula.

-- Jeff, in Minneapolis

DrRocket
2008-Sep-15, 06:56 PM
This may well be silly question but I can’t figure it out (I’m not the brightest person).

The premise I understand to be true is:

a) the Universe was infinitely small and had infinite energy “just prior” to the BB
b) just after the BB, the Universe inflated (as per the BB inflation theory) at a colossal rate and then calmed down to a more tranquil inflation process

The question then is if the universe was infinitely small, how did it get to the size we see today ?

I thought that anything either infinitely small or large (or with any infinite parameter) will not change no matter what you do it precisely because of this infinite characteristic.
Example, halve a infinite group of atoms and you still have an infinite group of atoms.

What am I missing here ?

The same applies for the energy at the singularity of a black hole. I understand that at the singularity, energy becomes infinite. But considering that the amount of energy entering a black hole or producing a black hole is not infinite, where does this energy come from ?

I don't believe that there is anything in the Big Bang hypothesis that leads to a conclusion that the universe every contained an infinite amount of energy. Density and energy density (matter and energy are really the same thing per relativity) can be infinite without either mass or energy being infinite, if the volume is zero.

It does not logically follow that if the volume is zero at time 0 that it must remain so forever. This is related to the notion of a contraction in the branch of topology called homotopy theory. Consider the function F defined for t between 0 and 1 inclusive and X any vector in 3-space (or n-space if you like) defined by F(t,X)=tX. F is a continuous deformation of 3-space to a point (or expansion from a point depending on how you look at it). F(0,X)=0 and F(1,X)=1.

Now, this does not say that the singularity that is predicted by general relativity is physically, valid. That is likely a matter that will not be resolved until there is a valid theory of quantum gravity or some other unification of general relativity and quantum mechanics. What it does say is that there is no mathematical or geometric obstruction to an expansion of the universe from a point. Note that in the example in the preceding paragraph F(t, . ) is just a change of scale for any non-zero t, and the resulting space is in fact ordinary 3-space, infinite in extent, with only a change in the length scale.

Cougar
2008-Sep-15, 07:19 PM
However, the proportions of abundance of the nuclear isotopes of
hydrogen, deuterium, helium, and lithium suggest very strongly that
the density, temperature, and pressure must have been within a
quite narrow range of values during the first few minutes, so even
if we don't know what the conditions were at time zero, we can be
pretty sure what they were a minute or so later.
This is correct, and those abundances imply things must have been cooling rapidly (otherwise the universe-wide abundances of these elements would be different than what we observe). Remarkably, based on the above-referenced observations, most theoretical cosmologists (Susskind, Vilenkin, Steinhardt, Turok, Smolin, to name a few) are in agreement about the state of the Universe just one second after its mysterious beginning (if it was even the real beginning, which is not an absolute fact by a long shot).

EvilEye
2008-Sep-15, 07:46 PM
We are still in that singularity.

By saying that, I mean that by trying to place it as an object "in space" is erronious.

We measure our universe from the inside. It's just bigger now than it was before.... from our point of view.... and still expanding.

If there were some sort of "outside" the universe would be one single point in infinity anyway.

thorkil2
2008-Sep-15, 08:35 PM
Was just about to post the same observation: The idea of the point origin of the Universe is meaningless unless there is an external frame of reference from which to reference it. I've repeatedly heard (from physicists working in this field, no less) how the Universe started as a pin point or the size of a dime, or some other such nonsense. The expansion was entirely internal, because from any reference frame within the Universe, there is no "external," and I would offer tentatively that since distance is a function of time, that the Big Bang had more to do with the unfolding of time and that 3-dimensional space is a consequence, but perhaps that should be relegated to ATM.

thorkil2
2008-Sep-15, 08:43 PM
The Hollywood version of the BB as an exploding fireball is nonsense.

spratleyj
2008-Sep-15, 11:02 PM
I've gotten two different explanations of the big bang and I'm not sure which is correct... 1) there was a tiny "point" in space with near infinite density 2) the "particles" were spread out in space and then expanded...

Let me note that the 2nd was the explanation given by Dr. Humprehyes so it may not be reliable at all... the 1st from various dumbed down big bang articles and books...

EvilEye
2008-Sep-15, 11:07 PM
The Hollywood version of the BB as an exploding fireball is nonsense.


That's why I prefer (and wish science would change the term to...) S.E.

Sudden Expansion

Cougar
2008-Sep-15, 11:27 PM
I've gotten two different explanations of the big bang and I'm not sure which is correct... 1) there was a tiny "point" in space with near infinite density 2) the "particles" were spread out in space and then expanded...
Both wrong, each in more ways than one. :) ]. The big bang is a theory about the evolution of the Universe, NOT about the "creation" or beginning of the Universe.

The theory points out that the initial expansion is poorly described by the idea of sending matter from somewhere flying out into some existing space... No! All space is more sensibly thought to come into existence in conjunction with the matter. At "time-zero," the question of one thing coming before another reduces to nonsense.

If you really must know, ;) the matter is thought to have resulted from the huge amount of energy released from the sudden decay of the extremely high energy vacuum field to the nearly zero low energy vacuum we find ourselves in today.

EvilEye
2008-Sep-15, 11:34 PM
And this is why we are searching for the Higgs Boson. "Matter Is Fatter"

Space itself is something that pushes things apart. Like anti-gravity. (but not really)

We haven't had enough time to see the entire evolution of our universe from beginning to end to understand how it works.

Again... from being inside it ourselves, we can only calculate what HAS happened, and then guess what will happen.

Where it began is ...again, a superflouis question. It's like asking who you were before you were concieved.

thorkil2
2008-Sep-16, 03:58 AM
That's why I prefer (and wish science would change the term to...) S.E.

Sudden Expansion

The incrediblely thing is that there are real physicists out there who subscribe to the fireball view (at least based on the way they describe the BB).

apolloman
2008-Sep-16, 08:44 AM
thanks for all the replies.

I'll read them all carefully and hopefully get things right this time.

EvilEye
2008-Sep-17, 03:02 AM
The incrediblely thing is that there are real physicists out there who subscribe to the fireball view (at least based on the way they describe the BB).


That's because it was incredibly hot... but not because it was an explosion.

If you blow up a balloon, and measure the temperature of the skin (the skin is our universe) .... it will rise as it expands. Same with a rubber-band.

That's what they mean.

But the bigger it gets, the cooler it gets, until it cannot cool anymore.

That's the end.

thorkil2
2008-Sep-17, 07:56 AM
That's because it was incredibly hot... but not because it was an explosion.

If you blow up a balloon, and measure the temperature of the skin (the skin is our universe) .... it will rise as it expands. Same with a rubber-band.

That's what they mean.

But the bigger it gets, the cooler it gets, until it cannot cool anymore.

That's the end.

I'm assuming there is a typo in this. I'd have to think about whether the skin of a balloon might increase in temperature as it expands, but the dynamics are not the same as those of the Universe, and the temperature of the Universe definitely did not go up as it expanded, as you noted subsequently. It's temperature curve was continuously downward from the BB. In any event, some of the descriptions I've read (from some of those same pinpoint/dime people) are descriptions of an explosion. Now I guess I have to back that up, which will take some digging.

(Not to digress, but it seems to me the problem of measuring temperature changes on the surface of an inflating balloon would take some very creative experiment. If I blow it up directly, the gasses entering the balloon are influenced by my own body temperature, so it warms. If I use a compressed source like a tank, the temperature of the gasses entering drops as the compressed gas expands, since the pressure in the balloon is less than that in the tank, so would cool the surface. The compression of the gas by the elastic balloon as it enters from either source causes an increase in temperature. It would take some pretty sensitive measurements and a lot of fudge factor to get a measurement of temperature change due solely to the elastic change in the surface. Probably easier just to take a sheet of balloon rubber and stretch it wthout all the inflation factors. Anyway, unrelated to the universe or this thread; sorry for the digression, but it caught my interest.)

EvilEye
2008-Sep-18, 03:04 AM
It was more of analogy, which is hard to put into math terms anyone could understand.

Yes.. the temp went down. But the sudden expansion created the heat, and has been cooling gradually since seconds after.

I was just trying to make it (the analogy) simple. I made the mistake of not giving a detailed timeline.

thorkil2
2008-Sep-18, 03:46 AM
Yes.. the temp went down. But the sudden expansion created the heat, and has been cooling gradually since seconds after.


I'm having a little trouble with that one, I'm afraid, but am I missing something in the difference between heat and temperature? Just can't buy that the expansion caused the heat. But then again, with all that heat, I've never bought into the vacuum fluctuation as a source of the BB, either.

mc^2
2008-Sep-19, 10:08 AM
The initial "singularity" associated with the Big Bang in any FRW GR model is actually something very very special... it is a singularity for which the space-time curvature tensor describes zero curvature and infinite compression.

Jeff Root
2008-Sep-19, 01:59 PM
EvilEye,

I think you are just a bit confused about how temperature relates to
compression and expansion. When you compress a gas, its temperature
increases. When you allow a gas to expand, its temperature decreases.

Pump air into a metal tank or a rubber balloon or tire. It becomes hot as
the pump compresses it. As the air sits in the tank or balloon or tire, it
slowly cools off until it is the same temperature as the surrounding air.
When you release the compressed air from the tank, balloon, or tire, it
becomes cold as it decompresses.

Why the Big Bang started out hot is unknown. Expansion cooled it.

-- Jeff, in Minneapolis

EvilEye
2008-Sep-29, 06:56 PM
EvilEye,

I think you are just a bit confused about how temperature relates to
compression and expansion. When you compress a gas, its temperature
increases. When you allow a gas to expand, its temperature decreases.

Pump air into a metal tank or a rubber balloon or tire. It becomes hot as
the pump compresses it. As the air sits in the tank or balloon or tire, it
slowly cools off until it is the same temperature as the surrounding air.
When you release the compressed air from the tank, balloon, or tire, it
becomes cold as it decompresses.

Why the Big Bang started out hot is unknown. Expansion cooled it.

-- Jeff, in Minneapolis


I understand that. I'm speaking of the very first moment of the big expansion.

It wasn't anything in the balloon. It is the balloon itself. There could be no temperature with no time, and no space. The expansion itself must have created the heat and has been cooling since as it expands farther.

OK.. stretch a rubber band very quickly, and it will be extremely hot, but begins cooling as soon as it reaches it hottest.

thorkil2
2008-Sep-29, 07:12 PM
Wouldn't it be easier and make more sense to ascribe the temperature and the expansion to the same initial condition rather than make one responsible for the other when there is nothing in known physics that would permit that? Remember, when you stretch a rubber band, you are putting energy into it from an external source, whereas the temperature and expansion of the big bang were entirely internal--self-contained. The rubber band analogy won't fly.