light crazy

[Bob Hegwood]

So did I cause the loss if interest in this topic with my Brain-Dead question?

Was a serious question, and I didn't mean to put anyone off of this topic. I
mean, we're looking at such a HUGE event, that we have absolutely no
idea what existed before the Big Bang, right?

Sorry if the question is irrelevant, or stupid, but I really am interested
in an answer.

Thanks, Bob

[Evil Dr Ganymede]

Was a serious question, and I didn't mean to put anyone off of this topic. I mean, we're looking at such a HUGE event, that we have absolutely no idea what existed before the Big Bang, right?

I've heard it said that by definition, whatever existed before the big bang (if anything) is irrelevant to our universe, because it cannot be detected, and no trace or evidence is left.

But keep one thing in mind - there technically IS no "before the big bang", because time itself (along with space) was created by the event. Time simply didn't exist before the Big Bang occurred. Neither did space - which means that space is being created as the universe expands. It's not expanding INTO anything.

[alphap1us]

Another Brain-Dead question...

If you set off an explosion here on Earth, the initial event starts with matter and energy speeding up and out in all directions as the explosion event unfolds.

If the universe is currently speeding up in its expansion, isn't this a lot like
what happens when an explosion on the Earth first begins? First, everything gathers speed, then it gradually slows down because of gravity and friction within the atmosphere, etc.

Could it be that Einstein's "Cosmological Constant" is simply a way to
describe the first few "seconds" of the event (as it happens on Earth) in
terms which are relevant to this gigantic explosion?

In other words, maybe we're still seeing just the first few seconds of the
Big Bang, and we don't know enough about what exists around
the explosion (i.e. - the environment in which it occurred) to understand
what's going on here.

Thanks, Bob

Bob,
Actually your question is very penetrating. The fate of the universe was an open question during the early part of the twentieth century. There were three models of what it could do. Basically it could expand for a while until gravity pulled everything back together, OR it could come to an equilibrium, where everything pretty much stopped, blanaced between the initial momentum outward and the force of gravity, OR it could keep expanding forever. The way physicist liked to phrase it is "Do we live in a matter or energy dominated universe?" To use your analogy, imagine putting dynamite under a rock. If you put a little, the wieght of the rock is large compared with the energy of the dynamite (The system is matter dominated). The rock will fall back to the ground. If you put just the right amount, the rock could go into orbit. OR, you could put so much, that the rock never stops going. This is an energy dominated system. (Kind of implausible but it's an analogy.)

Cosmology is the same way. If the universe is matter dominated, the force of gravity between the galaxies will pull them back together. Otherwise they will reach equilibirum or keep flying apart.

So, we need to find out which kind of universe we live in. Eventuallly, due to observations, it became clear that our universe is definitely on the third track. The real kicker is that we are even farther on the third track then physics can explain. Imagine looking at your rock with a telescope and finding that it was going faster than right after you detonated the dynamite. That'd be a real head-scratcher eh? Well that's the universe we live in. The galaxies are going away from us faster all the time and we don't know why.

Cosmologists call the thing that makes the galaxies travel away faster (=space expand more and more) dark energy. Some people complain that it is unphysical to talk about things that we can't measure etc. They don't understand that dark matter is just the name for "whatever it is that makes the univrerse expand like that." We'll think of a better name when we know more about its characteristics.

There is a very good explanation of all these things that confuse the whole human race at Prof. Sean Carroll's website. I recommend it for anyone who wants a very clear way to understand all these things.
http://pancake.uchicago.edu/~carroll/cfcp/primer/

Cheers,
Joe

[Bob Hegwood]

I've heard it said that by definition, whatever existed before the big bang (if anything) is irrelevant to our universe, because it cannot be detected, and no trace or evidence is left.

Sorry, but I don't understand how it can be "irrelevant" if this is where the
event occurred. There would have had to have been some kind of
place\time\environment in which the Big Bang occurred... Yes?

But keep one thing in mind - there technically IS no "before the big bang", because time itself (along with space) was created by the event. Time simply didn't exist before the Big Bang occurred. Neither did space - which means that space is being created as the universe expands. It's not expanding INTO anything.

Excuse me, but how do you know that it's not expanding INTO
anything? Certainly we don't have the technology to be able to see the
borders of the Universe yet, but that doesn't mean that something
might yet exist beyond the borders does it?

Let me try to use my explosion analogy again...

If the Sun were the size of an atom in the middle of a nuclear explosion,
and the Earth were the size of an electron, how would we know
that anything existed outside of the explosion? We wouldn't have the
knowledge or technology to see beyond the "mushroom cloud" so to
speak.

At any rate, thanks very much for the answer. I do think that this is a
fascinating discussion.

Thanks, Bob

[Bob Hegwood]

The real kicker is that we are even farther on the third track then physics can explain. Imagine looking at your rock with a telescope and finding that it was going faster than right after you detonated the dynamite. That'd be a real head-scratcher eh? Well that's the universe we live in. The galaxies are going away from us faster all the time and we don't know why.

But when an explosion occurs, doesn't the event unfold as follows?:

First, everything is at rest.
Second, the explosion causes particles to accelerate outward
from the center of the explosion.
Third, gravity, friction, etc. cause the particles to slow down.

Could it be that we're still seeing the second stage? That's what I was
trying to ask here. And, since we have no idea what kind of environment
the universe exists in, why is it a surprise that events may not be
unfolding as we expected?

Cosmologists call the thing that makes the galaxies travel away faster (=space expand more and more) dark energy. Some people complain that it is unphysical to talk about things that we can't measure etc. They don't understand that dark matter is just the name for "whatever it is that makes the univrerse expand like that." We'll think of a better name when we know more about its characteristics.

As I recall, Dark Energy is the name given to the force which
cosmologists use to describe the acceleration, yes? What is Dark Matter?

Thanks for the link... I'll go have a look.

Take care, Bob

[andersa]

Sorry, but I don't understand how it can be "irrelevant" if this is where the
event occurred. There would have had to have been some kind of
place\time\environment in which the Big Bang occurred... Yes?

Not necessarily, if space-time itself (as we know it) is indeed created by the Big Bang.

Consider the Earth for another analogy. We stand on its surface, making observations and trying to figure out what it's like deep down under our feet. We can imagine this heap of matter forming a rough sphere under the influence of gravity, and we believe we can tell what the core looks like all the way down to the center of the Earth.

But then somebody asks: What is it like beneath the center of the Earth? Why is it that we can't go any further than some 6,350 km "down" before we magically start going "up" again? Aren't our drills strong enough? Is it an alien conspiracy plot to prevent us from reaching below the zero radius..?

Like the mass of the Earth rests on its central point, the entire space-time of the universe rests on that point we call the Big Bang, at least according to theory (and I don't claim to fully understand that theory myself, but it sounds reasonable). If you can't visit the center of the Earth, try to travel further north from the North Pole, and you'll see what I mean.

[eburacum45]

But keep one thing in mind - there technically IS no "before the big bang", because time itself (along with space) was created by the event. Time simply didn't exist before the Big Bang occurred. Neither did space - which means that space is being created as the universe expands. It's not expanding INTO anything.

As an aside, the New Scientist mentions a theory called quantum Resurrection; apparently after a very very very long time a new universe could arise spontaneously, long after any of these various ends have played themselves out;

quantum fluctuations would happen on a smaller scale during the interim period, producing smaller objects; but a whole new big bang could occur at random after 10e10e56 years, creating a whole new universe.

It seems fairly obvious that (if this theory is right) our own present universe is the result of a random fluctuation in an empty dead universe, and there have been some/many/an infinite number of universes before, and there will be some/many/an infinite number of universes after our own.

Sean Carroll of the University of Chicago seems to be interested in this idea;
see this link.
http://www-news.uchicago.edu/releases/0 ... time.shtml

[Bob Hegwood]

Not necessarily, if space-time itself (as we know it) is indeed created by the Big Bang.

Okay, that makes some sense to me, as long as you're saying "as we know it."

Like the mass of the Earth rests on its central point, the entire space-time of the universe rests on that point we call the Big Bang, at least according to theory (and I don't claim to fully understand that theory myself, but it sounds reasonable). If you can't visit the center of the Earth, try to travel further north from the North Pole, and you'll see what I mean.

But we know what's happening when we get to the North Pole, and we
know why we start going South if we continue on our journey... This probably
was NOT the case at some point in the past, because we hadn't learned
enough about our environment. That's really all I'm saying here. I don't
understand how someone can say that nothing exists outside of our
universe if we haven't learned enough about it to make an informed
decision.

Does that make sense?

Take care, Bob

[alphap1us]

The real kicker is that we are even farther on the third track then physics can explain. Imagine looking at your rock with a telescope and finding that it was going faster than right after you detonated the dynamite. That'd be a real head-scratcher eh? Well that's the universe we live in. The galaxies are going away from us faster all the time and we don't know why.

But when an explosion occurs, doesn't the event unfold as follows?:

First, everything is at rest.
Second, the explosion causes particles to accelerate outward
from the center of the explosion.
Third, gravity, friction, etc. cause the particles to slow down.

Could it be that we're still seeing the second stage? That's what I was
trying to ask here. And, since we have no idea what kind of environment
the universe exists in, why is it a surprise that events may not be
unfolding as we expected?

Bob, I think you are confused about some of the mechanics terms we are using. When you detononate the dynamite, all its energy is transferred in a hundredth of second to the rock. This is the only time that acceleration happens. Otherwise, the rock is travelling at constant velocity, minus the effects of gravity, friction, etc.
So, are we still in the second stage? Dark Energy is a way of getting around the question. Something is causing the universe to expand at much greater than constant velocity over a very long period of time and the dnymaite/rock analogy breaks down.

As I recall, Dark Energy is the name given to the force which
cosmologists use to describe the acceleration, yes? What is Dark Matter?

Yeah I don't know why I wrote dark matter there. If you want to find out what it is, read the Carroll introduction. he will probably expalin it better than I could. If you are still confused, ask me here.

Cheers,
Joe

[alphap1us]

But we know what's happening when we get to the North Pole, and we
know why we start going South if we continue on our journey... This probably
was NOT the case at some point in the past, because we hadn't learned
enough about our environment. That's really all I'm saying here. I don't
understand how someone can say that nothing exists outside of our
universe if we haven't learned enough about it to make an informed
decision.

Bob, you are touching on an extremely delicate point here. When a physicist says the "universe," they mean by definition the entire environment in which we exist. It may seem hubristic to make claims about all of creation when we can only see the part we can, but you have to consider the alternative. That alternative is making claims based on some supernatural principle that we can't observe, and we all know where that leads....

You might also say that one alternative could be reserving judgment until we know more. In one sense we are reserving judgemet, since a physicist is always ready to be proven wrong, if some can make a better claim that is supported by reliable evidence. So ,there is always a sense that we are just doing the best we can for now. And when we see more things, hopefully we can make better guesses.

Cheers,
Joe

[Evil Dr Ganymede]

Sorry, but I don't understand how it can be "irrelevant" if this is where the event occurred. There would have had to have been some kind of place\time\environment in which the Big Bang occurred... Yes?

It's irrelevant in the sense that there's no trace at all left of it. There is no physical or detectable evidence of any material from "before" our universe was created, and it would seem that it's impossible to detect it (and we probably wouldn't even recognise it if we saw it )

Excuse me, but how do you know that it's not expanding INTO anything? Certainly we don't have the technology to be able to see the borders of the Universe yet, but that doesn't mean that something might yet exist beyond the borders does it?

Because you need Space to exist for something to expand into . The universe IS space-time - as yet there's no concept of a "super-space" in which space-time itself it's expanding through. (I don't think there is, at least).

Just to boggle you further though, I've heard one theory (I think it's called membrane theory) that suggests that dark matter/energy may actually the manifestation in our universe of the gravitational influence of mass in OTHER universes beyond our own. Kinda like the shadow of a force, acting on matter in our universe...

[Bob Hegwood]

Bob, I think you are confused about some of the mechanics terms we are using. When you detononate the dynamite, all its energy is transferred in a hundredth of second to the rock.

Okay then Joe, let me re-phrase it then... Could it be that we are still
experiencing the 1/100th of a second? I mean, how would we know what
time frame is involved in a previously (to us) non-existent environment?

If you want to find out what it is, read the Carroll introduction. he will probably expalin it better than I could. If you are still confused, ask me here.

Again, thanks very much for that link. I have indeed been persuing
the pages, and I've also added the link to my web site. Is a very nice
resource for those of us without formal training.

Take care, Bob

[Bob Hegwood]

It's irrelevant in the sense that there's no trace at all left of it. There is no physical or detectable evidence of any material from "before" our universe was created, and it would seem that it's impossible to detect it (and we probably wouldn't even recognise it if we saw it )

But once again, how do we know that there's no trace of it left?
Seems to me that Dark Matter and Dark Energy could be plausible
candidates ...

I understand that I'm out of my depth here, but I'm greatful for these
replies. If I had had the opportunities, I'd have loved to become a
Cosmologist. Still simply fascinating stuff.

Thanks, Bob

[Evil Dr Ganymede]

It's irrelevant in the sense that there's no trace at all left of it. There is no physical or detectable evidence of any material from "before" our universe was created, and it would seem that it's impossible to detect it (and we probably wouldn't even recognise it if we saw it )

But once again, how do we know that there's no trace of it left?
Seems to me that Dark Matter and Dark Energy could be plausible
candidates ...

They could be, I guess. But it's quite likely we'd never be able to prove that was the case, since we don't know what anything in a previous universe looked or behaved like, or what form it would be in having survived the transition to this universe (Well, apart from Galactus... ).

I understand that I'm out of my depth here, but I'm greatful for these replies. If I had had the opportunities, I'd have loved to become a
Cosmologist. Still simply fascinating stuff.

Trust me, it takes a rare breed to be a cosmologist - there's a ridiculous amount of maths and high-concept stuff going on there... I did a course on that in my MSc and while I could understand a few of the concepts, most of it was just complete gobbledigook to me. I think it's much more fun to just talk about the wacky implications and various Big Ideas like this .

[t00fri]

...
If I had had the opportunities, I'd have loved to become a
Cosmologist. Still simply fascinating stuff.

Thanks, Bob

Bob,

while I have kept quiet during that discussion for various reasons, I wholeheartedly agree with you as to the fascination of Cosmology!

In fact what I am referring to is not the classical Cosmology that is based on an effective, thermodynamic input for the Universe (pressure, density , equation of state, Boltzman's equations...) together with Einstein's general relativity and the picture of 'Inflation'. That's all fine and it's scope is well understood.

The "new" cosmology, usually now called "Particle Cosmology" has recently become an enormously booming theoretical field worldwide. It is most actively pursued at the world's leading theoretical physics institutes...

Why is it so fascinating?

Well, first of all, as the name says, one addresses the most basic and puzzling questions of Cosmology within the truly /microscopic/ and highly successful framework of theoretical Particle physics, notably also including String theory. Within the traditional framework of describing the Universe as a thermodynamic environment (gas, liquid, radiation) the depth of possible results is /necessarily/ limited. Such an /effective/ description of the Universe can never penetrate to the very origin of those questions. Only Particle Physics with its truly microscopic framework of Quantum Field Theory and String Theory has a chance of success.

The field has recently received a lot of new impact, for various reasons:

Experimentally:
-----------------
-- The amazing highly accurate results on the early universe from the cosmic microwave background experiments (BOOMERANG, MAXIMA,WMAP).

From these we know that the geometry of the universe is /flat/ with high precision and the picture altogether strikingly agrees with that of 'Inflation'. We now have precision results on crucial cosmological paramters, including, of course, the amount of matter density and notably of Dark Energy.

-- The large scale stcructure experiments [SDSS] beautifully complement these results and together lead to a strikingly consistent set of experimental precision constraints.

-- The Type Ia SuperNova data again fit into the picture and had provided the first evidence that the Universe is accelerating (i.e. nonvanishing "Dark Energy")

-- Many experiments demonstrating compelling evidence for Dark Matter, the nature of which being still unknown. Fact is that most of the Universe's matter is dark i.e. NOT luminous!

Theoretically:
----------------

From these recent precision experiments, a set of basic cosmological questions have emerged where theoretical Particle physics holds considerable promise for a solution!

-- What is Dark Energy? Why is it so small? What sets the scale? Could it be related to the tiny mass of neutrinos??

--What is the mechanism for the striking matter-antimatter asymmetry in the Universe? Could it be related to the tiny mass of neutrinos ("Leptogenesis"!)?

-- What is Dark Matter? Is it composed of the new kinds of particles predicted by Supersymmetry? The forthcoming gigantic particle colliders (LHC@CERN,...) will most probably find an answer.

-- Why are the dark energy density of the Universe and its matter density about equal TODAY??

-- What dynamics sets the initial conditions for 'Inflation' to work as needed by experiments? String Theory?

-- What is the role of extra space-time dimensions? Could the small dark energy be a remnant from higher dimension dynamics?

String Theory is formulated in 10 space-time dimensions with 6 of them 'curling up' in the process of 'compactification, such that we are left with 3 space +1 time dimensions.

-- What is the nature of the Big Bang? Was there a Universe before the Big Bang that underwent a Big Crunch (before being 'recreated' with a Big Bang)? Hence, when was the beginning of time??

Only String Theory has presently the potential to provide answers related to Big Bang issues. It allows to explicitly study the Universe close to space-time singularities like we picture the Big Bang.


So there is lots of exciting theoretical and experimental work ahead of us!

Bye Fridger

[Michael Kilderry]

-- What is the nature of the Big Bang? Will there be a Big Crunch? Was there a Universe before the Big Bang?

There is also a big rip theory in which the universe's accleration increases to the extent of the Milky Way galaxy and solar system flying apart, the earth exploding and all matter breaking up. If this is the end of the Universe it is predicted to happen in 20 billion years.

Michael Kilderry

[t00fri]

-- What is the nature of the Big Bang? Will there be a Big Crunch? Was there a Universe before the Big Bang?

There is also a big rip theory in which the universe's accleration increases to the extent of the Milky Way galaxy and solar system flying apart, the earth exploding and all matter breaking up. If this is the end of the Universe it is predicted to happen in 20 billion years.

Michael Kilderry

I was talking about serious theoretical physics, not stuff speculated about e.g. by sci-fi authors...
But you will barely be able to appreciate the difference

Bye Fridger

[Michael Kilderry]

It may sound fake, but it actually is a proper scientific theory, I read it on space.com, I'll see if I can track down the article and put down a direct link.

Michael Kilderry

[t00fri]

It may sound fake, but it actually is a proper scientific theory, I read it on space.com, I'll see if I can track down the article and put down a direct link.

Michael Kilderry

Never mind. If I did not mention it, it is not anything very serious... Just take my word for it [ Don't forget that my field of theoretical research includes this area...]. I admit, it is perhaps not explicitly excluded yet.

Sorry, but I don't care about popular Space sites with science writers that more or /less/ understand what they are writing about...

I guess you are implicitly referring to those rather exotic papers ("phantom cosmologies") by Robert R. Caldwell/Dartmouth College & collaborators, entitled "Phantom Energy and Cosmic Doomsday" e.g.
http://xxx.lanl.gov/ps/astro-ph/0302506
[Phys.Rev. Lett. 91 071301 (2003)]

In their view, dark energy is "phantom energy", in which the sum of the pressure and energy density is negative.
In other words, the equation-of-state parameter w=p/rho, the ratio of the dark-energy pressure p to its energy density rho is assumed < -1. A value w<-1/3 is required for cosmic acceleration.

The assumption of "phantom energy", w<-1, violates the socalled "dominant energy condition", rho >= |p| , that prevents the theory to become unstable. It was later found that only very contrived scenarios might be able to "live" with w < -1...

Well,...Sci-fi writers will be all exited about the implications of that "theory".

Again, this kind of speculations are not based on a microscopic field theory framework, but rather once more on the thermodynamic language (pressure, density, equation of state...) of classical cosmology.

Bye Fridger

[Evil Dr Ganymede]

If you want to find out more about all this, but put in more understandable/accessible terms, I strongly recommend getting the "The Elegant Universe" book by Dr Brian Greene (there's also a PBS TV series made from that, apparently). I thought it was a very good explanation of quantum mechanics, string theory, folded up dimensions and where this branch of physics seems to be going. I don't think it requires much more understanding of science than "A Brief History of Time" would.