Inflation, Expansion, Dark Matter and Dark Energy

[reddog12]

There are obviously some smart people here.

By what process could Inflation possibly happen in the initial time following the Big Bang?

Also, how is it that the continuing expansion of the Universe is now seen to be accelerating faster now than in the past?

And does anyone have a clue what Dark Matter and Dark Energy really are?

Thanks.

[arahant]

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There are obviously some smart people here.

By what process could Inflation possibly happen in the initial time following the Big Bang?

[/ QUOTE ]
The standard explanation is that there was a phase transition that, in addition to forming much of the matter that exists today, released an enormous amount of energy. This energy resulted in the expansion. You know, like an explosion (analogy only). A nice lay explanation here: Link (http://abyss.uoregon.edu/~js/cosmo/lectures/lec21.html)

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Also, how is it that the continuing expansion of the Universe is now seen to be accelerating faster now than in the past?

[/ QUOTE ] Well, that is an active research problem. The most frequently mooted explanations are dark energy and a positive cosmological constant (a term in general relativity that was added, and then removed, as a 'fudge' factor). Short answer...we don't know.

As an aside, while you may have just misspoken, it's not thought to be accelerating faster than in the past. It's just that in the past, theory indicated 0 or negative acceleration, but observation indicated otherwise.

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And does anyone have a clue what Dark Matter and Dark Energy really are?

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I do, but I'd prefer not to say. Knowledge is power, you know.
Seriously though, 'no'...they are also basically 'fudge factors'. ("expansion is accelerating, so we got missing energy...galaxies are rotating at the wrong speed...how about some more matter"). Some people postulate that dark matter consists of undetected elementary particles...Wikipedia gives a nice summary of both of the current state on both of these I think, but I'm tired, so you'll have to get there without a link /images/graemlins/smile.gif.

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Thanks.

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It was my pleasure. I hope this brief answer provides you years of lasting happiness.

[evank15]

http://upload.wikimedia.org/wikipedia/commons/b/b9/GalacticRotation2.svg

That is what dark matter is. A is the predicted model, B is the observed data. As far as we know the only thing that can account for the discrepancy is dark matter. By the way, that is a rotation curve for a typical spiral galaxy ripped from wikipedia.

Dark matter interacts only gravitationally, otherwise it has zero effect (as far as we know I guess) on baryonic (visible etc) matter.

I guess I didn't answer any of your questions, just adding to the discussion.

[FortunaMaximus]

Now what would non-visible matter that only has gravitational effects be doing in an Universe?

[arahant]

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Now what would non-visible matter that only has gravitational effects be doing in an Universe?

[/ QUOTE ] Just hanging out?

[FortunaMaximus]

Something like that, probably hiding in the shadows. Damn WIMPs. Anyway, I'm puzzling it over. Might have something for Boro and evan to chew apart in a day or a week.

[reddog12]

Not to sound stupid, but do we actually know what gravity is?

Also, no one has mentioned anything about dark energy.
What the hell is it?

I mean, to me, it appears that really we have almost no clue about the universe we find ourselves in.

What if the universe has 12 dimensions, and we can only detect four?

Maybe we're a few centuries away from figuring it out, or maybe we'll never know - it's beyond our comprehension.

[MoreGentilythanU]

"Also, no one has mentioned anything about dark energy.
What the hell is it?"

I think someone mentioned this before but it's just a fancy term to explain why the universe is accellerating despite the fact that the only action at distance force in the universe -Gravity- pulls things together.

[arahant]

[ QUOTE ]
Not to sound stupid, but do we actually know what gravity is?

Also, no one has mentioned anything about dark energy.
What the hell is it?

I mean, to me, it appears that really we have almost no clue about the universe we find ourselves in.

What if the universe has 12 dimensions, and we can only detect four?

Maybe we're a few centuries away from figuring it out, or maybe we'll never know - it's beyond our comprehension.

[/ QUOTE ]

Well, yeah. It's a tough problem!
In terms of 'knowing what gravity is', I would have to say 'yes, we do'. It's described very well mathematically. I think there are a lot of things in physics that people expect to be able to 'understand' on some intuitive level, and that will never be the case. Walter Hess has a quote to the effect of 'much exists in the world that we'll never be able to comprehend, because our cerebral organization is devised only to secure the survival of the individual in it's surroundings'.

Even if physics fills in all the holes we have in our understanding, it's unlikely to provide an explanation that people find intellectually satisfying. The questions people want to ask of physics aren't really appropriate questions. When you say, 'what is dark energy', 'what is gravity'...it's as though you are looking for an explanation in terms of things we see every day, like particles.

Still I think it's safe to say that there are some big gaps in our understanding, but compared to our understanding 500 years ago, the progress has been absolutely stunning. Seeing the way people work, the missteps and errors that even very bright people routinely make, it amazes me that we've come so far in our understanding.

We basically have a model that works, and explains almost all the phenomena we see. The things we still want to explain are so distant as to border on the philosophical (dark matter, neutral kaon decay, etc...).

[FortunaMaximus]

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Well, yeah. It's a tough problem!

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No kidding. It's probably up there right now as one of the toughest problems in science.

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We basically have a model that works, and explains almost all the phenomena we see. The things we still want to explain are so distant as to border on the philosophical (dark matter, neutral kaon decay, etc...).

[/ QUOTE ]

Well, that's a good thing, as that was true of all raw posits and postulates before they became provable theories. Sure, it seems unachieveable today, but I don't think the solutions are so distant and far-off they cannot be achieved in a reasonable amount of time. Half a century maybe, and that's pessimistic.

Um, although at this point I'm more interested in quantum and temporal theory than anything else, the more that physics lays the framework for the Universe, the more reasonable the questions that are asked, can be asked with the shoulders of previous theories to stand on.

At least at this stage, we can recognize there are gaps, and to some extent, realize where they are, and the paths towards filling them are becoming clearer and better defined.

Of course, the Holy Grail is the GUT. Grand Unified Theory. While we may not have the complete theory, we're getting there, aren't we? At least we know now that there is a theory that will explain everything.

It may very well end up being 42, but looking at the number 42, there are an innumerable number of ways one can get to 42. /images/graemlins/tongue.gif Sometimes the greatest of theortical gold is hidden in fiction.