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HelloKitty
30-10-2005, 03:05:52
Polls for many years have shown that a majority of Americans are at odds with key scientific theory. For example, as CBS poll this month found that 51 percent of respondents believed humans were created in their present form by God. A further 30 percent said their creation was guided by God. Only 15 percent thought humans evolved from less advanced life forms over millions of years.

Other polls show that only around a third of American adults accept the Big Bang theory of the origin of the universe, even though the concept is virtually uncontested by scientists worldwide.

Koshko
30-10-2005, 04:28:16
What I want to know is what started the Big Bang?

Sir Penguin
30-10-2005, 05:13:03
Nothing. It was.

SP

Lazarus and the Gimp
30-10-2005, 07:03:08
Answers like that always strike me as being a bit of a cop-out.

Vincent
30-10-2005, 10:46:44
Bah, who cares. Just because it's the big bang it's nothing special. I can't change it back anyway. It's not an important question like "Will this be a good bottle of wine?" or "Who has borrowed my copy of Age of Mythology?"

zmama
30-10-2005, 11:13:37
Yes

Shakey

The Norks
30-10-2005, 12:16:53
I thought the big bang was increasingly discredited?

KrazyHorse@home
30-10-2005, 12:57:22
Originally posted by The Norks
I thought the big bang was increasingly discredited?

Not true.

There are still a few whackos out there who believe otherwise (a few whackos with physics PhDs, that is) but given the data from WMAP and supernova distance-redshift observations it's increasingly difficult to create models whereby the Universe didn't undergo a big bang.

Venom
30-10-2005, 13:50:16
Yes, well the earth is still flat so that's cool.

KrazyHorse@home
30-10-2005, 13:51:48
The Earth isn't flat. The Universe is, though.

HelloKitty
30-10-2005, 19:18:13
YOU MOMMA"S FLAT!

Vincent
30-10-2005, 19:52:20
and got big banged

Koshko
30-10-2005, 20:16:15
Originally posted by KrazyHorse@home
Not true.

There are still a few whackos out there who believe otherwise (a few whackos with physics PhDs, that is) but given the data from WMAP and supernova distance-redshift observations it's increasingly difficult to create models whereby the Universe didn't undergo a big bang.

Okay but that still doesn't explain what triggered the Big Bang to start. I mean if energy is neither created or destroyed, how did energy come to exist in the first place?

KrazyHorse@home
30-10-2005, 20:53:37
a) I'm not sure energy was created by the big bang. Depending on your exact cosmological model the Universe might have a total energy of 0

b) I'm not making any speculations as to what caused the Big Bang. I was merely responding to Norks' assertion that the Big Bang theory was increasingly discredited.

Koshko
30-10-2005, 23:53:04
Maybe God created the Big Bang and then started the various evalutionary processes throughout the Universe. Tripping the Rift!

HelloKitty
31-10-2005, 00:54:37
Koshko, part of the majority!

The Norks
31-10-2005, 22:28:49
I read recently that there were several credible theories about the 'creation' of the universe and all its stuffs, and that the Big Bang theory was slowly being eroded as a complete or likely explanation. Something to do with mobius strips or time folding over or something, and the universe not necessarily just expanding infinitely. Of course I can't back this up with anything because I read it in passing. It makes sense tho, its a bit arrogant to think that a few hundred years of science and we cracked it.

....Twice now I've written Big Band theory and had to correct it because the idea of an orchestra creating the universe is a bit disturbing.... maybe thats what really happened to Glenn Miller?!

KrazyHorse@home
31-10-2005, 22:31:12
I think you're reading about crackpot theories.

The Big Bang is gaining more and more acceptance because we have better and better data to back it up.

At least, that's my sense of it. But what the hell do I know. I'm just a graduate student doing research in cosmology. ;)

KrazyHorse@home
31-10-2005, 22:42:08
The real new developments have been inflation and the existence of dark energy.

Vincent
31-10-2005, 22:50:59
I always have a lot of dark energy

KrazyHorse@home
31-10-2005, 23:05:02
Fundamentally inflation is the thought that the early Universe expanded extremely rapidly for a very short period of time during a period in which the density and temperature of the Universe was so large that there was a bunch of physics we're a little bit fuzzy on going on. After this tiny, tiny, tiny fraction of a fraction of a second "normal" physics took over and the Universe proceeded according to processes which we understand pretty well. This takes care of the horizon problem (the Universe is uniform on larger scales than we would expect) and the flatness problem (the Universe is flatter than we would expect)

Dark energy seems to be some sort of vacuum energy (it has a negative pressure). We're not quite sure what it is, but we see its effects on the expansion curve of the Universe (the Universe appears to actually be accelerating in its expansion; since the matter density goes down as the Universe expands, but the dark energy density remains a constant, at some relatively recent time during the expansion the dark energy began to dominate the Universe and thus force it into an accelerating mode)

DaShi
01-11-2005, 04:42:18
He's a witch!

Koshko
01-11-2005, 04:45:35
What if our universe expands and contracts in size like a sine wave?

KrazyHorse@home
01-11-2005, 06:28:38
Not quite a sine wave, but that can happen given certain cosmological parameters.

That situation is strongly contraindicated by the best measurements we have now.

Nills Lagerbaak
01-11-2005, 09:17:31
Although what seems to be confusing things at the moment is the apparant fact that the expansion of the universe is not slowing down (as would have been expected if all the energy in the universe was created in the initial bang).

And as for what was before the big bang, well, that's the area of philosophers and theologins. Unless of course you believe that the big bang was just one of an infinite number of big bangs...

Greg W
01-11-2005, 09:20:35
The big gang bang?

Gary
01-11-2005, 09:23:34
I suspect you need an infinite number of 'Big Bangs' in order to get the infinite number of universes you need to have one like this :)

Of course they're not sequential though (assuming that means anything).

KrazyHorse@home
01-11-2005, 09:33:56
Originally posted by Nills Lagerbaak
Although what seems to be confusing things at the moment is the apparant fact that the expansion of the universe is not slowing down (as would have been expected if all the energy in the universe was created in the initial bang).

It's not confusing at all. There are valid quantum reasons to expect there to be a "cost of having space", i.e. a vacuum energy i.e. a cosmological constant.

The real mindfuck is that the cosmological constant we would expect from current understandings of quantum field theory and the cosmological constant actually observed differ from each other slightly. Like by 35 orders of magnitude.

Nills Lagerbaak
01-11-2005, 09:49:20
hmm, I thought they were trying to explain it by the existence of some other force....dark matter.

Also how is the force exerted by a vacume defined?

Oerdin
01-11-2005, 10:16:22
Originally posted by Koshko
Maybe God created the Big Bang and then started the various evalutionary processes throughout the Universe. Tripping the Rift!

But when were Adam and Eve riding dinosaurs like horses? I saw a spcial on TV about the religious nutters of America and those people were convinced the Earth was 5k years old, Humans used to ride Dinos like horses, and that the rapture was coming any days now (so no need for new enviromental laws). They even built a little bible theme park with fiberglass dinos complete with saddles to prove humans & dinosaurs co-existed. They also had statues of Adam & Eve naked but without genitals. I guess no one had sex or pissed prior to the fall of man.

Oerdin
01-11-2005, 10:21:58
Originally posted by Nills Lagerbaak
Although what seems to be confusing things at the moment is the apparant fact that the expansion of the universe is not slowing down (as would have been expected if all the energy in the universe was created in the initial bang).

And as for what was before the big bang, well, that's the area of philosophers and theologins. Unless of course you believe that the big bang was just one of an infinite number of big bangs...

I thought that depended upon how fast the universe was expanding. If it was expanding slow enough that gravity could pull it back together then we'd have a big crunch, if they were in balance then the universe would be static, and if it was expanding fast enough then gravity could never pull it back together again.

Supposedly, there isn't enough matter in the universe for gravity to slow it down and pull it back together again but the new monkey wrench is how much dark matter exists. I, unlike someone here, am not a cosmology student so that's the National Geographic version. ;)

KrazyHorse@home
01-11-2005, 10:40:12
Originally posted by Nills Lagerbaak
hmm, I thought they were trying to explain it by the existence of some other force....dark matter.

Also how is the force exerted by a vacume defined?

You mean dark energy.

The point with dark energy is that we're simply saying we don't know for sure what it is. It could be the energy of the vacuum. It could be something else (though its behaviour is strangely similar to what you would expect from a zero-point energy)

If the scale of the vacuum energy and the scale of dark energy were similar then this discussion would be over. Unfortunately, it's not. So either the existence of dark energy means that there's a hitherto unknown field with some strange properties or that for some reason our understanding of how to calculate the zero-point energy is wrong. Multiplying entities without need is not something I do, so I choose b.

However, the scientific community would like further investigation of this subject (for good reason) so we're looking into it. If we can nail down dark energy even further to show that it behaves very very similarly to how the energy of the vacuum should behave then we'll have further proof that the particle physicists need to search for answers within their field. If we can show that dark energy has some quirky behaviour that's not what we'd expect from vacuum energy then we'll have something to talk about.

There is a pressure associated with a vacuum energy because: if its energy density is a constant rho (this is what we expect) then the total energy in the vacuum is rhoV where V is the volume of the universe. The pressure exerted is -dE/dV = -rho

KrazyHorse@home
01-11-2005, 10:43:52
Dark matter is nothing special. It has no funny cosmological properties. It's simply matter which has such a low interaction cross-section that it doesn't interact meaningfully with the "baryonic" (i.e. visible) Universe.

For instance, ~2% of dark matter is simply thermal neutrinos. The rest is other shit which interacts at even lower scales.

Nills Lagerbaak
01-11-2005, 10:44:50
Well, I';m no expert on things cosmological, but here's how I understand it.
Initially it was thought there were only 4 forces.
Inter mollecular (Nuclear force)
Gravitational (between masses)
Electromagnetic (Between charges)
Radio-active decay force.

All things being equal the universe should slow down once the initial bang happened (As you cannot create energy)
But as the universe is not slowing down, they think there might be some other force acting on the system....

I could havr this all wrong though

KrazyHorse@home
01-11-2005, 10:45:49
Nothing really too interesting about it. It would be nice to actually see it, but that's probably beyond our capabilities right now. Its existence is confirmed in many, many ways (galactic evolution being one of the most important ones)

KrazyHorse@home
01-11-2005, 11:01:09
Originally posted by Nills Lagerbaak
Well, I';m no expert on things cosmological, but here's how I understand it.
Initially it was thought there were only 4 forces.
Inter mollecular (Nuclear force)
Gravitational (between masses)
Electromagnetic (Between charges)
Radio-active decay force.

All things being equal the universe should slow down once the initial bang happened (As you cannot create energy)
But as the universe is not slowing down, they think there might be some other force acting on the system....

I could havr this all wrong though

There doesn't have to be a new "force" in the sense of having a new gauge boson which obeys its own interaction rules.

What there does have to be is some sort of energy density on the order of 0.699*10^-26 kg/m^3. If this energy density exists and is relatively constant in time then it implies a Universe which is undergoing an accelerating expansion (as time goes on and the vacuum term dominates more and more then it comes closer and closer to an exponential expansion). Current QFT would predict an energy of the vacuum which is ridiculously (in fact, catastrophically) large. There are ways to fix this large vacuum energy density. Unfortunately those ways involve making the vacuum energy density 0. Making it slightly larger than 0 is hard and reeks of fine-tuning (which is bad). Either we don't exactly understand QFT or this energy density is something new.

Nills Lagerbaak
01-11-2005, 11:33:16
I'm not sure I fully undestand vacume force.

How do you relate the force on 1g of matter of a certain density in a perfect vacume? Or does a perfect vacume not exist. But if it does then surely the force could be as large as you like?

Nills Lagerbaak
01-11-2005, 11:33:50
Oh, and how far would the vacume succeed in pulling the matter apart? Down to a quark level....

KrazyHorse@home
01-11-2005, 11:47:54
Originally posted by Nills Lagerbaak
I'm not sure I fully undestand vacume force.

It's not a force. It's an energy density. Being a constant energy density it has a negative pressure. This negative pressure causes the Universe to accelerate.

(d^2a/dt^2)/a = -4piG/3(rho + 3p)

where p is the pressure, a is the scale factor, rho is the density and G is the gravitational constant

the left hand side is basically the acceleration of the universe. If the right hand side is negative then the universe is slowing down. If it's positive then the Universe is speeding up.

How do you relate the force on 1g of matter of a certain density in a perfect vacume? Or does a perfect vacume not exist. But if it does then surely the force could be as large as you like?

You're trying to do classical mechanics here.

This is General Relativity, son. Trying to describe the expansion of the universe by appealing to force arguments is just plain impossible.

Nills Lagerbaak
01-11-2005, 11:53:38
Aha, fair enough in a universal scale, but can I ask you the same question but concerning 1 gramme of matter in a perfect vacume in laboratory conditions. But I suppose the greater a vacume you create the more force you require to create it.

KrazyHorse@home
01-11-2005, 11:54:06
Originally posted by Nills Lagerbaak
Oh, and how far would the vacume succeed in pulling the matter apart? Down to a quark level....

Bound states are practically unaffected by the expansion of the Universe. The Hubble constant is vanishingly small.

KrazyHorse@home
01-11-2005, 11:56:29
Originally posted by Nills Lagerbaak
Aha, fair enough in a universal scale, but can I ask you the same question but concerning 1 gramme of matter in a perfect vacume in laboratory conditions. But I suppose the greater a vacume you create the more force you require to create it. ?

What?

Eh?

I have no idea what you're on about here.

King_Ghidra
01-11-2005, 11:58:26
let's start using the word vacuum now huh, just you know, for the hell of it

Nills Lagerbaak
01-11-2005, 11:59:13
I thinking of a hypothetical situation. You have a vacume in a jar and you put a solid piece of matter in it. I assume that the force holding the matter together is greater than the force that the vacume is exerting on it.

Try the same thing but with say jelly. What would happen?

KrazyHorse@home
01-11-2005, 12:08:55
Vacuum energy is just as present inside a piece of matter as it is elsewhere.

KrazyHorse@home
01-11-2005, 12:10:02
So a change in the volume of the matter in the jar does not change the vacuum energy inside the jar. So E is independent of Vmatter. So the pressure on Vmatter is 0.

Nills Lagerbaak
01-11-2005, 12:11:06
ah yes, indeed it is. What is it caused by though Gravity?

KrazyHorse@home
01-11-2005, 12:11:14
The vacuum energy only has a measurable effect when you can change the volume of space itself.

KrazyHorse@home
01-11-2005, 12:12:43
Originally posted by Nills Lagerbaak
ah yes, indeed it is. What is it caused by though Gravity?

Vacuum energy is a result of the bubbling about of quantum fields. Known quantum fields like electrons and photons and quarks and... Or at least maybe it is. But if it is then there's something wrong with how we do the calculation to find its value. And if it's not that then it's something else. Maybe. Who knows?

KrazyHorse@home
01-11-2005, 12:16:19
Gravity is not well understood in terms of quantum fields. To say the least. So it's fair to say that the vacuum energy is caused by everything except gravity. Maybe.

Nills Lagerbaak
01-11-2005, 12:23:13
Mind....exploding....vacume too strong.....

MoSe
02-11-2005, 15:17:18
Originally posted by Nills Lagerbaak
Also how is the force exerted by a vacume defined?

"it sucks"

Dyl Ulenspiegel
02-11-2005, 15:18:40
Quantum suck, the key to understanding the universe.

Rub bish
02-11-2005, 15:25:01
rubbish

Dyl Ulenspiegel
02-11-2005, 15:43:18
star rubbish

Rub bish
02-11-2005, 15:55:00
darkstar rubbish