Questions on Dark Energy...

[rrw4rusty]

Hi!

 

Question 1:

Correct me if I'm wrong but it seems like its assumed that Dark Energy is now over powering Dark Matter so that Dark Energy is 'pushing' the universe outward rather then 'pulling' it outward. If this is so, why is the pushing (or, if I have it back wards, pulling) assumed?

 

Question 2:

I believe that current theory says that about 5 billion years ago (that time frame could be wrong) the clumpy dark matter's gravity, weakened by the expanding universe, was over powered by the constant dark energy and the accelerating runaway expansion began. One of the things that led to the discovery of dark matter was the way galaxies rotate -- the outer stars rotated at the same speed as the inner stars. Since dark energy now overpowers dark matter wouldn't we see this anomaly in galactic rotation begin to vanish. Also, if 5 billion years ago, dark energy had no effect because dark matter still over powered it, would galaxies rotate differently than they do today?

 

Question 3:

Is the expansion of space between galactic clusters driven by the creation of new space/time and is this related to the separation of virtual particle pairs?

 

Thanks!

Rusty

[timo]

Question 1:

Correct me if I'm wrong but it seems like its assumed that Dark Energy is now over powering Dark Matter so that Dark Energy is 'pushing' the universe outward rather then 'pulling' it outward. If this is so, why is the pushing (or, if I have it back wards, pulling) assumed?

When constructing sensible equations for the gravitational field there is one degree of freedom left over; say an integration constant. This constant can not be directly linked to any known physical entity but does affect the physics. Since it is (read: seems generally considered) somewhat unsatisfactory to have a physically non-further-specified mathematical possibility affect actual physics, one sometimes assumes this constant is caused by some yet-unknown physical entity or mechanism which is then called "dark energy".

 

 

Question 2:

...

I don't understand most of what you say. Some general remark: It is usually quite meaningless to compare forces without any given scope (typical silly statements often found are "the electromagnetic force is much stronger than the gravitational one"). You question seems to have a scope at some point at least: For the rotation of galaxies you can completely forget dark energy influence.

 

Is the expansion of space between galactic clusters driven by the creation of new space/time and is this related to the separation of virtual particle pairs

It would probably be consistent with being interpreted as creation of new space. Not sure about new time because as far as I know you already talk about space expanding with time, not about spacetime expanding with ... well, what? That said, I do not know if that actually is a common interpretation.

The expansion is not explained by or attributed to mainstream particle physics. In some quantum gravity it would probably be related to the creation of something, but probably real and not virtual stuff.

[Arch2008]

Question 1:

General Relativity indicates that the universe must expand or contract. Hubble discovered that it was in fact expanding. When the rate of expansion was measured, it was discovered that the universe was not slowing down as was expected due to the gravitational forces in play, but that the rate of expansion was actually increasing. From the observed rate of expansion and the estimated mass of the known universe, a value for the amount of energy that could cause this phenomenom was calculated. The observations and calculations seem to be more than substantiated by the WMAP results, so Dark Energy's effect is more than just assumed.

 

Question 2:

Dark Energy has not "overpowered" the effect of Dark Matter on a galaxy's spin. Dark Energy may be the energy of empty space. As the amount of empty space increases due to the expansion of the universe, so does the amount of Dark Energy. The greater the amount of DE, the greater the expansion. If DE doesn't "decay" into something with normal mass, then in about 22 billion years it will be stronger than the nuclear force that binds atoms together. Currently, DE is not strong enough to overpower atoms or galaxy spin.

 

Question 3:

Supposedly, if you think of a unit of space as an energy grid, when a virtual particle pair is created, the particles temporarily "borrow" energy from the grid and the energy of the grid slumps. When the particles recombine and annihilate, the energy is returned to the grid, sort of like a wave function. As this continues, a "negative pressure" is created that stretches or inflates the space. So the existing space time is bent by the effect of gravity and stretched or inflated by the effect of DE.

[rrw4rusty]

Arch2008,

 

Edit: I must have been having an LSD flashback -- all references to 'your first post' are references to Atheist's post -- the reply before yours (sorry Atheist!).

 

Thank you for your reply and the effort put into your thoughtful answers!

 

Edit: In response to your first post... kindly replace 'space/time' with just 'space' if the expansion of the universe only involves 'space'... perhaps I use the term space/time too loosely though I thought space and time were so closely related affecting one always affected the other.

 

Question 1:

<snip> so Dark Energy's effect is more than just assumed.

 

Absolutely, but, if I'm catching all of your answer, that wasn't my question. The acceleration of the U-Expansion could be caused by (a) DE pushing outward from within, (b) DE pulling outward from the outside*, or © both. (a) seems to be 'assumed' or choosen... is there a particular reason?

 

* say, just for the sake of an example, the universe was really a bubble in sea of infinite mass of infinite density... its gravity would 'pull' (instead of push) at the matter in the universe.

 

Edit: I now see that in your first response you say (I think) that it is preferable or customary to use what is already there and since 'pulling from outside' assumes that there is something 'outside' then, 'pushing from within' is used because we know we have 'stuff' within. At least I think that is what you're saying... if all that makes sense. Hopefully I haven't missed anything else you've said.

 

Question 2:

<snip> Currently, DE is not strong enough to overpower atoms or galaxy spin.

 

Awesome and informative answer! But someday it will, yes? In watching the Universe show on the History channel it stated that about 5 billion years ago the DE overpowered DM (at some level) and the acceleration of the expansion of the universe started up (or began increasing). Do you know how this 5 billion year time span was determined? (btw, '5' is what I think the show said... it might have been '4' or '7' or ?)

 

Question 3:

Supposedly, if you think of a unit of space as an energy grid, when a virtual particle pair is created, the particles temporarily "borrow" energy from the grid and the energy of the grid slumps. When the particles recombine and annihilate, the energy is returned to the grid, sort of like a wave function. As this continues, a "negative pressure" is created that stretches or inflates the space. So the existing space time is bent by the effect of gravity and stretched or inflated by the effect of DE.

 

Hm... so you are saying that VPPs are created (adding themselves briefly to space/time) and then recombine and annihilate (subtracting themselves from space/time) and this '1-1' (so to speak) -- a break even affair -- creates a "negative pressure"? Its hard to see how adding two particles and subtracting two particles would result in anything. Can you elaborate?

 

Acually my exact question was (and you did answer though I seek clarification), just like a VPP appearing on an event horizon and being pulled apart (therefore really adding a particle to space/time), was this somehow occurring in the space between clusters (perhaps by some force exhorted by the absence of matter -- the vacuum) and this was the cause of the expansion (accelerating of course as this empty space expands). Does that make sense? I am assuming, perhaps incorrectly, that the expansion is because 'more' space/time is being created between clusters and such. Perhaps I am mistaken and space/time is somehow being stretched as it expands(?).

 

Thanks again for your efforts... and for avoiding equations -- I'm a technical writer attempting his first science fiction novel and a long time 'armchair' hobbyist of cosmology and quantum mechanics that rarely gets into the math.

 

Rusty

Edited October 1, 2009 by rrw4rusty
LSD flashback

[Arch2008]

Okay, we don’t have a way to interact with something that is hypothetically “outside” the universe, so a theory about a force “pulling outward from outside” would be total conjecture. If something cannot be disproved, then it may sound interesting, but it will never be science. So the only scientific approach is to deal with a force from within. There is a Dr. Randall who asks if gravity might be leaking into our universe from another dimension and I really hope that she will find a way to prove this;).

 

As for the time when the rate of expansion of the universe began increasing, I believe that the best indicator was data from Type 1a Supernovae. SN’s in galaxies farther away were dimmer than they should have been. It was determined that this dimness could only be accounted for if the SN’s were actually farther away than expected. Instead of the expansion of the universe slowing, as expected, it was actually accelerating. If the effect of DE continues to increase, some think that in about 22 billion years the atoms may fly apart in a “Big Rip”.

 

Negative pressure is quantum mechanics and not my hobby. That said, here goes. Think of the fabric of space time not as something solid, like a brick, but instead as something more like a sponge. Energy for VPP is “squeezed” out of it and then the energy is again “soaked” back up. In this scenario, space time is elastic. Theoretically, General Relativity shows how space time can be bent and twisted by gravity, particularly near a black hole. So an anti-gravitational force like DE “stretches” space time. Any random, minute overstretching temporarily causes more space time that is then filled with DE. The more DE you have, the greater the rate of expansion. Perhaps there was ever only one small speck of space time. Gravity and DE have “molded” it over billions of years into the universe we see today.

 

I hope that this helps.

[Tugrul]

Question 3:

Is the expansion of space between galactic clusters driven by the creation of new space/time and is this related to the separation of virtual particle pairs?

 

I am going to use the baloon example again

 

Okay you have an uninflated baloon, draw two dots right next to each other. Then blow the baloon up, now look at the dots before the baloon was blown up they were right next to each other now they are far away.

 

Baloon=Universe/multiverse

Dot=Galactic cluster

 

Thank you