Big bang and infinite space

[PurpleBuddha]

When I hear a physicist describing how big the universe may be, I am always puzzled when they mention the possibility that it may be infinite, but not because of the difficulty in grasping the concept of infinity.

Now I understand the difference between the observable universe and the non-observable universe, and why the universe can be much larger than 28 billion light years even if it only started 14 billion or so years ago.

However, for it to be infinite wouldn't the big bang model have to be wrong? When the universe began to expand, it had a finite size. How can something finite in size ever turn into something infinite in size? If by infinite they are including the possibility of the multi-verse and that there may be an infinite number of other universes, than I can gel with that. But it always seems that they are talking about this universe because the topic seems to come up when they mention the unobservable universe being unobservable because it is too far away for the light to reach us.

 

[T'Girl]

I think of it like this, before the "big-bang" the limitless empty universe was already there. The big bang put physical material into this infinite empty space.

Now how dark matter figures into this little hypothesis of mine I'm not sure. As I understand it (or don't) dark matter is what is making the growing sphere of physical material, galaxies-gases-energy, expand faster and faster.

 

[Bones2]

I've always understood the Big Bang to be an expansion rather than an explosion. So rather than being matter growing out and occupying previously empty space, it's actually all of existence expanding.

But then, I don't really know a lot, so I'm almost certainly wrong.

 

[Trekker4747]

I've always understood the Big Bang to be an expansion rather than an explosion. So rather than being matter growing out and occupying previously empty space, it's actually all of existence expanding.

But then, I don't really know a lot, so I'm almost certainly wrong.

That's how I, more-or-less, understand it. There was an "explosion" at the Begining, but that explosion is expanding the very fabric of the universe rather than matter expanding out into infinite nothingness.

It's less "explosion into air" and more... blowing up a balloon.

 

[chrisspringob]

When I hear a physicist describing how big the universe may be, I am always puzzled when they mention the possibility that it may be infinite, but not because of the difficulty in grasping the concept of infinity.

Now I understand the difference between the observable universe and the non-observable universe, and why the universe can be much larger than 28 billion light years even if it only started 14 billion or so years ago.

However, for it to be infinite wouldn't the big bang model have to be wrong? When the universe began to expand, it had a finite size. How can something finite in size ever turn into something infinite in size?

No, the bolded part is what you have wrong. The idea is that the universe is now and has always been infinite, but that "the space has been stretching" as USS Bones put it.

To put it another way, imagine that the universe is permeated by a giant 3-dimensional grid, and the distance between any two grid points is some nominal comoving distance times some scale factor. The scale factor just keeps getting bigger and bigger from its initial value of zero at the moment of the Big Bang. But the grid extends infinitely far in every direction, so from one instant after the Big Bang, the universe was infinite.

 

[Bones2]

It's less "explosion into air" and more... blowing up a balloon.

Yeah, blowing up a balloon. That's the perfect analogy for it as I understand it. And it's unlikely that we're both wrong.

 

[Meredith]

Space can be "Closed" and yet infinite!!

Imagine if the universe was the size of a broom closet and you were in it, you could reach forward and touch your own back! And you would be standing on your own head!

I am thinking the universe is closed yet infinte!

 

[ProtoAvatar]

When I hear a physicist describing how big the universe may be, I am always puzzled when they mention the possibility that it may be infinite, but not because of the difficulty in grasping the concept of infinity.

In what context exactly have you heard that the universe is infinite?

Before the big bang, there was no matter or energy, not even space and time. There was..nothing. At least, our mathemetical desciptions of nature can't reach that far and quantify what was.

Then came the big bang - and the universe came into being; but it was NOT instantly infinite. We know that simply because the universe is too uniform.
Have you heard of inflation - http://en.wikipedia.org/wiki/Inflation_%28cosmology%29 ? It attempts to explain why the universe is so homogenous, given its size; if the universe was infinite from the start, this uniformity would be impossible.

Nowadays, space just keeps...appearing. What was 1 meter some time ago, now it's two meters.

There is a theory according to which the universe is closed. Imagine the universe as having only two spatial dimensions. 'Closed' means that the universe is shaped like a sphere - this means that no matter how far you go, you'll never reach its end - you'll just go in cirlcles; 'infinity' in a maner of speaking.

 

[Jadzia]

You have to take time into consideration when we think of space. There's the idea that the farthest points are retreating from us at the speed of light, and since we cannot catch up with these, in that sense, it is infinite. Remember, there is no absolute concept of now, so we cannot talk about the universe without a perspective of time.

 

[Checkmate]

So what's on the "outside" of this balloon metaphor? What existed before the Big Bang? If it was true nothingness, how did somethingness appear? And why and how is it making it bigger if it was nothing to begin with? And wouldn't the nothingness be what's on the "outside" of the balloon, which would also be infinite in size in order to encompass the balloon as it expands? I get that the universe -- all the stuff that makes up the stuff we're aware of -- fits in with the balloon idea. But I don't see how space itself does. Not the space the universe currently fills, but space as a whole.

These are serious questions. I'm sorry if they sound sarcastic or anything. I've never been able to wrap my head around it.

 

[ProtoAvatar]

So what's on the "outside" of this balloon metaphor? What existed before the Big Bang? If it was true nothingness, how did somethingness appear? And why and how is it making it bigger if it was nothing to begin with? And wouldn't the nothingness be what's on the "outside" of the balloon, which would also be infinite in size in order to encompass the balloon as it expands? I get that the universe -- all the stuff that makes up the stuff we're aware of -- fits in with the balloon idea. But I don't see how space itself does. Not the space the universe currently fills, but space as a whole.

These are serious questions. I'm sorry if they sound sarcastic or anything. I've never been able to wrap my head around it.

The pre big bang 'nothingness' is defined as the absence of matter, energy, space and time. As I said, mathemetically, the time cannot be rewinded to provide a more complete description.

There is a speculative theory according to which vacuum fluctuations (aka the uncertainty principle) existed even then, and they provided the energy necessary for the big bang.

 

[Jadzia]

So what's on the "outside" of this balloon metaphor? What existed before the Big Bang? If it was true nothingness, how did somethingness appear?

As we continue to dig deeper into scientific truth, whatever theory we settle on, we can always then ask why things have to be that way and not another way. ie, what made it be like that.

No scientific explanation is ever complete, so it's never really an explanation at all.

One of my favourite quotes: "There is no explanation that does not itself have to be explained."

Except nothingness... An absence of space, time, matter, mind, geometry, number... and anything else. Nothingness doesn't need an explanation, because there isn't anything there to explain. The only valid starting point in a true explanation of reality, would be nothingness.

And somehow, nothingness has to mutate into what we have today. The crucial step... and perhaps the most mind bending concept in philosophy, is that nothingness must spontaneously change into something other than nothingness.

 

[Alpha_Geek]

I still sometimes think about the pulsing universe model and if it might be valid after all. Granted, much points away from it, but my monkey brain can't grok everything simply expanding into nothingness... ya know?

 

[Mr. Laser Beam]

What existed before the Big Bang?

The Big Foreplay.

 

[Trekker4747]

What existed before the Big Bang?

The Big Foreplay.

And right now we're in The Big We Can Just Cuddle.

 

[RoJoHen]

And somehow, nothingness has to mutate into what we have today. The crucial step... and perhaps the most mind bending concept in philosophy, is that nothingness must spontaneously change into something other than nothingness.

This is the part that makes my brain hurt.

 

[PurpleBuddha]

And somehow, nothingness has to mutate into what we have today. The crucial step... and perhaps the most mind bending concept in philosophy, is that nothingness must spontaneously change into something other than nothingness.

This is the part that makes my brain hurt.

I have been seeing more and more physicists rejecting the idea that before the big bang there was nothing, and then nothing turned into something. I find myself agreeing with them. There is, of course, no real evidence either way, but I go with what intuitively makes sense until someone comes along and demonstrates otherwise.

Anyway, as to the people mentioning the big bang acting more like an expanding balloon, I see that. Yet, that is what perplexes me. Early on this "balloon" was relatively small and then grew.

Check out this chart:

http://www.kheper.net/cosmos/universe/universe.htm

at 200 seconds after birth, the radius of the universe was 55 light years. At 500,000 years after birth, when the universe was still a wee little baby, it was 1,500,000 light years. And so it continued to grow. At what point can something that is finite become infinite?

I realize it is expanding faster than we could over take it if we tried to reach to the edge in some futuristic space ship, but just because it is faster than us, does not mean it has made the jump to infinity.

I guess I am still wondering perhaps what they mean when they say it "might" be infinite in size. How might this be true and the big bang model, which measures the size of the young universe (among other things) both be accurate?

The fact that space is curved, maybe to such a degree that it is closed, doesn't seem to make it infinite to me, any more than it makes the earth infinite. I think this addresses what Meredith was saying about touching yourself in the closet.

I hope that clarifies what I am saying a little. And I don't want people to think I am dug into a position here. I really want to understand what they mean when they say it might be infinite, and if this squares with the big bang model.

Edit: Isn't it mind boggling to imagine the universe expanding as far as 55 light years in a mere 200 seconds? Makes warp drive look pretty shitty.

 

[Lindley]

Well, there's your FTL drive: Just invent a time machine, hop back to the big bang, traverse a much smaller distance, hop back to the future, and you're suddenly really far away.....

 

[PurpleBuddha]

Nice.

Come to think of it, that is a cool illustration of how space and time are connected.

 

[Iasius]

I guess I am still wondering perhaps what they mean when they say it "might" be infinite in size. How might this be true and the big bang model, which measures the size of the young universe (among other things) both be accurate?

As far as I understand it, these figures given for the size of the universe at certain intervals after the big bang generally refer to the presently observable universe only. It would be surprising if the universe and the observable universe were one and the same, after all, we're at the center of the observable universe.

The entire universe seems to be much larger than the observable universe and may be infinite in size.