will the universe expand forever?

[atommo999]

as dark matter increases, it pushes our universe apart, but some scientists think that soon the creation of dark matter might slow, eventually leading to a big crunch.  even if this does happen, we wont be around long enough to experience it, but it is still interesting to know. it has been known that the universe is still accelerating away. at the bottom is a predicted picture of the universal acceleration if dark matter doesnt stop driving things apart. that is also known as "the big freeze" a point where everything is too cold to support anything.

dark matter: the properties of dark matter are yet to still be known.

link: http://en.wikipedia.org/wiki/Big_Crunch

[Alex_Ian_Hamilton]

Hi atommo999,
I think you've gotten confused with dark energy and dark matter, if you swap ever time you say matter for energy then you’re pretty much right.

The early cosmological models talked about how the universe was expanding from a point (at the time of the big bang) and that gravity was slowing this down; this meant that you had 3 options for how the universe could go:
If the energy of the explosion isn't able to overcome the force of gravity (which depends on the total mass of the universe) trying to pull it in, then the expansion of the Universe will eventually stop, then things will start to fall back down to the original point and we have a "big Crunch".
If there isn't enough mass (so not enough gravity), then the Universe never slows to a stop and just keeps getting bigger and bigger forever.
There is also the special case of a borderline, where there's enough mass (and gravity) to stop the expansion, but not ever fall back (this requires an exact amount of mass to energy).

20 years ago we thought we had it sussed and we just needed to figure out the mass of the universe and the rate the expansion is slowing down and we're set.
Then two teams using Supernova to measure the deceleration noticed something a bit wrong; the universes expansion is accelerating, something is pushing EVERYTHING apart more today than a few billion years ago.

So that's when we discovered Dark Energy (nothing to do with Dark Matter, it's just stuff the doesn’t make light, so it's dark); and we have no real idea what this is (there are some thoughts, but none work ATM).
http://en.wikipedia.org/wiki/Dark_energy

All we can say is that Dark Energy is increasing, so the universe isn't only expanding ATM, but actually accelerating...
This means that if dark energy doesn't stop (which may happen, we don't have a clue what it is) then there won't be a slowdown, let alone a crunch.

However if Dark Energy keeps growing, then we may eventually end up with the Universe expanding so fast that everything rips apart (the Big Rip).
http://en.wikipedia.org/wiki/Big_rip

It's all a big mystery tho, the biggest in the Universe and we didn’t have a clue until just 10 years ago, and I can't wait to get some answers. 

[Bla]

I think you mean dark energy, dark matter is matter which just doesn't interact with photons, and as e=mc^2 shows, matter cannot be created.
But dark energy is a force that works opposite of gravity, and it has been growing in our universe.
Well, you probably knew this already, just wrote matter instead of energy.

[atommo999]

yes i get confused by dark matter and dark energy as the same thing, however they are not. thanks for saying so i know for next time.

so dark matter: doesnt interact with anything and is non-luminous

dark energy: non-luminous but does interact with other things.

[Bla]

Dark matter also interacts with other things. Dark matter is like normal matter that doesn't interact with photons/light.
Dark energy (I think it's also called vacuum energy) just opposes gravity, making the universe expand faster like you wrote about in post 1.

[Alex_Ian_Hamilton]

Bla, you’re pretty much right, the fundamental thing about Dark Matter is that it doesn’t have any electromagnetic charge; because of this it doesn’t interact with electromagnetic radiation (light just passes straight through) and more-over it wouldn’t interact with the electrons of your body, so it actually would pass straight through your body and even the earth (remember that pressure and chemical bonds are all made by the action of electrons and their charge).
The experiments searching for Dark Matter (and finding none) show that it’s made of some totally new kind of stuff that is charge-less and doesn’t work with the strong nuclear force (that’s the force that holds protons in the nucleus, despite their charge wanting o push them apart); it does however interact through gravity (we can see it warping/bending light). It also doesn’t seem to interact with the weak nuclear force, because so-far we haven’t detected anything that we can pin down as Dark Matter.
Gravitational lensing seems to suggest that Dark Matter is mostly concentrated in a spherical cloud around every galaxy (unlike how flat and disk-like the stars are), but that there are filaments connecting between galaxies (kinda like a very loose cobweb) and that we are just travelling through dark matter all the time, but because it doesn’t interact with our particles, we don’t notice.

Dark energy is a total mystery, one of the theories is vacuum energy, but we have no real information to suggest that; also, the predicted value of vacuum energy is more that 10^100 times away from the real number (that’s 1 with a hundred zeroes), which means that we have something seriously wrong somewhere.
I highly recommend these for more info, hopefully I’ve not made any mistakes...
http://www.astronomycast.com/extragalactic/the-search-for-dark-matter/
http://www.astronomycast.com/cosmology/18/
Fingers crossed that the LHC (Large Hadron Collider, the new particle accelerator in Geniva) will shed some light on it... :-)

[Bla]

Thansk very much for the info! Very interesting.

[deoxy99]

Well, it depends on the factor Omega. Since I cannot remember what would happen if you changed the value, search it yourself! Search Astrophysics on google

[Bla]

This video is very interesting. It suggests how the universe can form from nothing, by the total energy in the universe being 0.
In that case, the universe will slow it's expansion, and like in a hyperbola it get's closer and closer to 0 in the rate of expansion. Or am I misunderstanding something?

Otherwise, an earlier universe might have caused the current one to exist.
But watch the video! It's one hour where you'll get a lot more clever, it's very very exciting. Highly recommended.

[deoxy99]

Bla, you’re pretty much right, the fundamental thing about Dark Matter is that it doesn’t have any electromagnetic charge; because of this it doesn’t interact with electromagnetic radiation (light just passes straight through) and more-over it wouldn’t interact with the electrons of your body, so it actually would pass straight through your body and even the earth (remember that pressure and chemical bonds are all made by the action of electrons and their charge).
The experiments searching for Dark Matter (and finding none) show that it’s made of some totally new kind of stuff that is charge-less and doesn’t work with the strong nuclear force (that’s the force that holds protons in the nucleus, despite their charge wanting o push them apart); it does however interact through gravity (we can see it warping/bending light). It also doesn’t seem to interact with the weak nuclear force, because so-far we haven’t detected anything that we can pin down as Dark Matter.
Gravitational lensing seems to suggest that Dark Matter is mostly concentrated in a spherical cloud around every galaxy (unlike how flat and disk-like the stars are), but that there are filaments connecting between galaxies (kinda like a very loose cobweb) and that we are just travelling through dark matter all the time, but because it doesn’t interact with our particles, we don’t notice.

Dark energy is a total mystery, one of the theories is vacuum energy, but we have no real information to suggest that; also, the predicted value of vacuum energy is more that 10^100 times away from the real number (that’s 1 with a hundred zeroes), which means that we have something seriously wrong somewhere.
I highly recommend these for more info, hopefully I’ve not made any mistakes...
http://www.astronomycast.com/extragalactic/the-search-for-dark-matter/
http://www.astronomycast.com/cosmology/18/
Fingers crossed that the LHC (Large Hadron Collider, the new particle accelerator in Geniva) will shed some light on it... :-)

Plus, LHC will find the higgs boson, the particle thought to give other particles mass.

[Alex_Ian_Hamilton]

Cosmology is my fav subject, I could talk about it for hours, and even longer if I have a balloon and a marker pen handy (just ask my friends... lol)
Tho do search cosmology, it’s quite a small part of astrophysics, despite dealing with EVERYTHING.

Yes, the expansion of the universe when plotted on a graph can make a hyperbola if the Universe will expand forever (a special shape of curve if you plot size of the universe vs time); or it can make a parabola if the Universe will fall back on itself.

I’ll have to watch that video, it looked interesting from the first 2 mins...
But I do think we’re stretching ourselves with hypothesising about what came before the Universe; I’ve heard of many groups trying to work the maths backwards, but the fact is that we don’t have any complete theories that can stretch back to t=0 (the start of the big-bang and the Universe), despite there being a whole load of clues around (the whole Universe is evidence); anything considering the time before the Big Bang is just speculation at this stage, even if very interesting speculation.

And personally I can’t wait for the LHC to be up and running at full compactly; it’s such a shame that it’s had so many problems (and such a bad show for science in the public media).
With the potential to find the Higgs Boson (to confirm our theories of mass), search for super-symmetric particles (heavy particles from String Theory that could make up Dark Matter) and possible detect extra dimensions... The LHC could be one really exciting experiment that may answer a lot about our Universe.

[atomic7732]

super-symmetric particles

Don't you mean the WIMP's?

[Alex_Ian_Hamilton]

Super-symmetric particles are actually a whole family of particles that are predicted by String Theory.

As I understand String Theory (and please note I’ve not studied it heavily), one of the predictions is that for every fundamental particle we know of today (electrons, photons, quarks, neutrinos), there is a heavier version (one with hundreds to thousands of times the mass).
These should be exactly the same as their lighter variants (have the same charge and such), so they should interact with matter in the same way (tho their mass would change things a bit); but one super-symmetric particle (namely the Neutralino, the super-heavy neutrino) would be a good candidate for dark matter, as it’d be charge-less, colour-less (that actually relates to the strong nuclear force, not the appearance) and generally act like a neutrino, but be very heavy. The Neutralino would also be considered a WIMP (Weakly Interacting Massive Particle); remember the term “WIMP” is just an empty name used to describe the properties of something we haven’t detected, where-as super-symmetric particles are the actual class/family... (much like I’m a web developer, but fundamentally I’m a human, it’s not an either/or situation)
http://en.wikipedia.org/wiki/Supersymmetry

The main thing is tho, that if super-symmetry doesn’t exist (if these heavy particles aren’t found), then we now that String Theory is wrong (or at least in need of a lot of changes)...