Any Astrophysicists in the house?

[Alecu]

This is actually the first time I manage to read about such things this year :biggrin: . Not too many people are interested in this :(.

 

About dark matter and dark energy. I read about dark matter in some books and the thing is that we can interact and see all the object because of the fundamental forces in the universe, electrical charge, weak nuclear force and strong nuclear force. Don't remember all of them exactly or their names. Gravity is a fundamental force too.

 

Most particles are affected by such forces and thus we can perceive them. The thing about dark matter is that it may be formed of particles that only interact with the rest through gravity. In a way such particles are totally "transparent" and "invisible". Some of these particles are called neutrinos I think. So even if they exist we would only be able to perceive the gravity that they exert.

 

Another idea is that dark matter has an incredible low density and an enormous volume. Since it composed out of particles that are probably way,way smaller than atoms it makes detecting them almost impossible because of all the "noise". Scientist have trouble isolating such particles and they have to somehow isolate the radiation/interaction so that they can be certain that indeed dark matter particles caused the interactions in their tests.

[marharth]

Offhand... Based on nothing I can really explain... The idea of an expanding and contracting universe might have merit... Meaning that there was already rotation present at the moment of the big bang, and what existed before the big bang was another universe which was collapsing into a singular point. Although there is a natural tendency toward atrophy, once the rate of spin was low enough to no longer enough to overcome the forces of gravity, the universe would slowly start to collapse again, as it collapses, the spin would start to increase again changing into centripetal force, drawing the universe together quicker and quicker until it coalesced into a super-massive singularity containing enough energy to tear itself apart again and giving rise to a new universe. So the energy we see could be a product of the circumstances related to the big bang. Where that energy came from initially, from countless cycles of expansion and contraction... Not a clue, but since we're talking about an event far beyond evidence, far before time even existed... You may as well just call it a creative constant that for all applicable purposes, always was (take that for whatever you want).

 

Since we have no real measure of the lifecycle of universes, and can only get an idea of an expanding one based on ancient light and background radiation that tells us it is still expanding, for all we know, our universe could merely only be in its early stages of continued expansion.

 

The thing is that we're talking about a universal scale here... Something so utterly vast that it encompasses everything within our understanding. Even when you consider the theory of a Multiverse, it's only relating other possible universes with our own, rather than trying to encompass all universes inside some even more vast system, with that system probably inside yet another... and so on, because when something works really REALLY well and the rules remain constant, it can be scaled up and down infinitely. We just don't know all the rules yet.

Well that is pretty interesting. Makes sense to me, I am trying to find more issues with what your saying but it seems like a good possibility.

 

Honestly I have never really thought dark matter and dark energy was enough to explain the universe being held together.

 

I guess one of the fundamental problems with these kinds of things is we simply don't know enough. We can't ever see the edge of the universe without violating the current laws of physics. The modern human brain can't even understand the idea of a thing without a start or a end.

[BlackRampage]

So here's the thing, I was walking from my class to my car and for some reason I started thinking about that whole Dark Energy thing... You know, the force which is causing distant galaxies to not only move further away from the center, but also moving further away from each other at an increasing rate contrary to gravitational mass. And I got to thinking... Could it be possible that this increasing rate might be due to a sort of universal rotation, such that some element of centrifugal force is being applied to galactic bodies which causes them to accelerate more the further away they get from the z axis?

Well, I'm no astrophysicist, but according to most theories nowadays dark energy is what is often called "the cost of having space".

In other words: That the volume of space itself has some kind of energy. It might sound strange at first but when you think about it, the expansion of the universe must take some kind of effort. In the effort of creating more space-time, dark energy is created.

 

It would also confirm the theory that dark energy is homogeneously distributed throughout the galaxy. (if dark energy takes the form of a "cosmological constant", that is)

 

Naturally this would mean that the more the universe expands, the more of this dark energy is created. Which is why the universe appears to be expanding at an ever increasing rate contrary to gravitational mass.

[Marxist ßastard]

IANAA either, but here goes:

 

Any cosmological model must satisfy the Einstein field equations. The Robertson-Walker metric is the simplest known solution to the Einstein field equations which can be made to match empirical observations about the whole universe. It's based almost entirely on the principle that on a large enough scale, space is homogeneous – that is, all points in the universe are equivalent. This precludes rotation like you're talking about, since it implies that the universe has no center or central axis. (It's also the simplest possible reason why every object in the universe moves away from Earth at a rate proportional to its distance, a result called Hubble's law.) Developing the RW metric further and adding dark energy yields the ΛCDM model, which explains a lot of phenomena in a relatively simple way and has a lot of consensus behind it. Dark energy explains the accelerating expansion of the universe, and models including dark energy perform quantitatively better than those without at predicting some empirical results. And as BlackRampage said, dark energy is just a way of saying that a vacuum has energy associated with it, which is actually pretty mundane.

 

Some solutions to the Einstein field equations involve rotation. The Gödel metric is one, and it has the potential to describe a universe very well – just not ours. It describes some very weird behavior and doesn't match up with Hubble's law. And it still includes dark energy. I can't tell you if all “rotating universe” solutions to the Einstein field equations violate Hubble's law and still include dark energy, but it's at least a starting point if you're still interested.

Edited October 22, 2011 by Marxist ßastard

[Vagrant0]

IANAA either, but here goes:

And it still includes dark energy. I can't tell you if all “rotating universe” solutions to the Einstein field equations violate Hubble's law and still include dark energy, but it's at least a starting point if you're still interested.

Like Einstein, math is not my strong suit and I wouldn't even know where to begin in working with most basic physics equations. Additionally the raw data available is not something I am intimate enough with, even if it were readily accessible to know how to factor it into those equations.

 

All points in space cannot be equivalent on any scale, but rather our ability to accurately measure those distances relative to eachother decreases as the scale increases. This is one of the reasons why relativity works well on large scale, but not on the extremely tiny, such as with sub atomic particles. This goes into that part of not knowing all the rules yet, we have two theories, Relativity for the large, Quantum for the small, but no complete singular theory. What I mean is that if we look at very small things, such as the parts that make up an atom, there is still space between the electrons and the nucleus, space between electrons, space between protons and neutrons, and space between those components in each. We have trouble determining the actual space between those things, but we know that they cannot all be equal to eachother based on what we can determine to the best of our ability.

 

I'm not suggesting that I have any better idea myself, but I was under the impression that part of the reason why both of these are theories rather than laws, was because there were instances where they don't work as well. I know this sounds dismissive of long-standing, popular beliefs, but isn't the point sometimes to try and suggest something outside the box and see if it holds water based on what we know to be true? I know there are all sorts of theories out there, but I would think that if this one wasn't valid, there would be an easy way to prove it based on the math involved. Yeah, i know... Applying Newtonian physics to a universal model seems like a step in the wrong direction but many of the theories which exist were based around creating a rational of explaining things which could not be empirically calculated at the time, or which were lacking some element to make them compute.

[Lisnpuppy]

Here Vagrant...write to these guys...no I am being serious (and not sarcastic or making light or anything as I love this stuff...but I can barely balance the checkbook. lol). Maybe you could actually start a dialogue with them. I mean..who knows. At least we know they can do the math.

 

http://www.bbc.co.uk/news/science-environment-15165371

[Marxist ßastard]

Actually, yeah, you could try to get in touch with the researchers. I'd be interested to hear any response you get back.

 

But in the meantime, since you're in school right now, you could just look in the time schedule and find a professor who teaches classes on astrophysics/cosmology. If one isn't available, any physics faculty with a doctorate would probably work. They could probably clear up all your lingering doubts in, like, 10 minutes.

 

I wouldn't even know where to begin in working with most basic physics equations

The point is that in general relativity, there is a finite number of models which could possibly describe the universe, and they all have to fit within a defined framework. You can't just make up a model and expect it to work out. And if you derive a model within the framework starting with a rotating system of particles, you may not have enough degrees of freedom left over to specify important stuff like conservation of mass-energy.

 

It's like wavefunctions in quantum mechanics: You can't say that the wavefunction of a particle is 4 - 2i ^0.75 - (x - 2)³. And you can't derive a wavefunction by saying that a particle has a position of exactly x and a momentum of exactly p.

 

All points in space cannot be equivalent on any scale

Okay, let me state this more clearly: If you divide the universe into cubes that are about a billion light-years to one side, the mass-energy density of the cubes will be about equal. And this is relevant to the RW metric because it's intended to describe the whole universe, and not individual objects within the universe. If you look at the ΛCDM model, there are ways to extend it to allow for large-scale variations in the mass-energy distribution. But at (relatively) smaller scales, you need to pick a solution to the Einstein equations which is specific to the phenomenon you're looking at.

 

But the more important result is that there is no center of the universe. If you don't see how that's possible, here's the standard analogy: Imagine that all the space in the universe is on the surface of a rubber balloon, and galaxies are points on that surface. As the balloon expands, all the points move away from each other. Points with greater surface distance from each other will appear to be moving away from each other proportionally faster. Thus the expansion is uniform – there is no center of expansion on the balloon's surface. Now take that curved 2D surface and imagine it's a flat 3D space. That's the universe.

 

part of the reason why both of these are theories rather than laws

Whoa, whoa, whoa. Stop right there. There's no such thing as a scientific law. General relativity and quantum dynamics are just as valid as gravitation, mass-energy conservation, Newton's laws of motion, and the laws of thermodynamics. Like any other scientific theory, they will become obsolete if and only if another theory describes empirical observations much better in every case. But that almost certainly won't happen: Most likely, they'll both survive as edge cases of a more general theory – just like they themselves both reduce to Newton's laws of motion for objects of mundane size and speed.

 

Why would they be so hard to displace? Well, atomic physics requires both general relativity and quantum mechanics; most of spectroscopy relies on quantum mechanics. If either were false, that would mean that all data ever produced in either of those fields (at least) would have to be discounted as a bunch of crazy coincidences. GPS and some other technologies rely on general relativity. Microchips are basically just flea circuses of weird quantum mechanics results. Quantum mechanics has predicted some empirical results down to 11 decimal places. For comparison, the Avogadro constant has 8 – so we're more confident in some parts of quantum mechanics than we are that matter is made up of atoms.

[Dark0ne]

(Complete off-topic and aside: Marxist...where the hell have you been and where have you come from? Your presence here brings back some serious nostalgia.)

[marharth]

(Complete off-topic and aside: Marxist...where the hell have you been and where have you come from? Your presence here brings back some serious nostalgia.)

I have seen him post quite a bit since I joined, I think he lurks a bit in the debate section :P

[Marxist ßastard]

(Complete off-topic and aside: Marxist...where the hell have you been and where have you come from? Your presence here brings back some serious nostalgia.)

What? Oh! Well, actually I'm posting from 2007. See, I'm caught up in a region of localized Gödel space with a closed timelike curve where my world line interacts with space in a... um, supersymmetry... and—

 

[sigh]

 

It's like The Lake House. Here's

; it pretty much gives the movie away. (Haha! That'll never get old!)

 

Oh hey, while I've got you guys from the future on here, can you tell me if gas prices go back down once the US gets out of Iraq? Gas is at, like, $3 a gallon right now and it's just so insane that people are really losing it. And it wouldn't be quite so bad if the jobs market weren't so terrible. I heard that most of the seniors this year only got 1, maybe 2 job offers before graduation. So unless they want to be out of work for 2 months or something (which sounds sorta good now that I think about it – vacation!) they're completely at that one company's mercy!

 

Actually, you know what? I don't want to change the timeline too much (temporal paradox, every proton in your body exploding in the speed of light, and all that), so just tell me, yes or no: Will gas go below $2 a gallon within the next 2 years?