Dark Energy

[jatmacha]

If Dark Energy is pushing everything apart in the universe then how is it that Galaxies are on a collision course with each other? Even Andromeda and milky way are said to be on a collision course with each other.

[imatfaal]

Andromeda and the Milky Way are actually quite close to each other! And yes, you are correctly they are gravitationally bound and will stay together, and even get closer.

 

The Dark Energy Expansion happens between clusters and superclusters with really enormous gaps between them. It is a background expansion when the space between things gets very slowly bigger. Any two objects that are held together by gravity will stay held together because the gravity is far stronger than the very gentle expansion. But when the gaps between galaxies/clusters are huge - there is both a lot of space to expand and the distance means that gravity between the two clusters is very weak; and in that case the gap grows. The universe is predominantly huge gaps! and these huge gaps are getting bigger - but anything gravitationally bound (like the solar system, the milky way, the local group of galaxies) will stay as it is because gravity is strnger

[CaptainPanic]

If Dark Energy is pushing everything apart in the universe then how is it that Galaxies are on a collision course with each other? Even Andromeda and milky way are said to be on a collision course with each other.

If you have a football stadium full of people, and they all go home after the match, individual people can still bump into each other hundreds of meters away from the stadium.

 

On average, everything is moving away from everything else. But individual stars or galaxies can still approach each other.

 

imatfaal - isn't random motion another reason?

[jatmacha]

Thankyou

[imatfaal]

...

imatfaal - isn't random motion another reason?

 

I don't know - but I don't think so. Where would the random motion come from? Everything is on an expansive course due to initial movement in the initial inflationary period - before Schmidt, Perlmutter and Reiss we were unsure whether residual motion would be greater and we would continue to expand at ever slower rates, or that gravity would win and we would grind to a halt and fall back in; we now think that dark energy is driving an accelerated expansion. But I do not see a place for random motion - about the only things that can account for a galaxy's motion is that it was already moving in the early stages of the universe, gravity, and now dark energy.

[CaptainPanic]

I don't know - but I don't think so. Where would the random motion come from?

Not sure. I am a chemical engineer, not an astronomer. If a gas expands, then the molecules will move away from each other - the density is being reduced. But at the same time, they still continuously crash into each other.

 

So, the way I see the expansion, of both a gas and the universe, is that there is an average expansion, but superimposed on that is some random motion. And for objects that are near each other, the movement caused by expansion is (relatively) small, whereas the random motion of two objects would have at least a factor which is no function of the distance between the two objects (and a factor, like gravity, which is).

 

Obviously, this "random motion" comes from somewhere. Could be gravitational interactions that happened in a (distant) past. Why is a gas molecule moving in the direction it is moving? I don't know.

 

But maybe I should stop using that term "random motion". It's a term used in chemistry (also called Brownian motion), not astronomy...

 

Everything is on an expansive course due to initial movement in the initial inflationary period - before Schmidt, Perlmutter and Reiss we were unsure whether residual motion would be greater and we would continue to expand at ever slower rates, or that gravity would win and we would grind to a halt and fall back in; we now think that dark energy is driving an accelerated expansion. But I do not see a place for random motion - about the only things that can account for a galaxy's motion is that it was already moving in the early stages of the universe, gravity, and now dark energy.

I agree that the state of the early universe will have determined where stuff is moving now.

 

Hope I didn't confuse things too much with my analogy with molecules.

[imatfaal]

Not sure. I am a chemical engineer, not an astronomer. If a gas expands, then the molecules will move away from each other - the density is being reduced. But at the same time, they still continuously crash into each other.

 

So, the way I see the expansion, of both a gas and the universe, is that there is an average expansion, but superimposed on that is some random motion. And for objects that are near each other, the movement caused by expansion is (relatively) small, whereas the random motion of two objects would have at least a factor which is no function of the distance between the two objects (and a factor, like gravity, which is).

 

Obviously, this "random motion" comes from somewhere. Could be gravitational interactions that happened in a (distant) past. Why is a gas molecule moving in the direction it is moving? I don't know.

 

But maybe I should stop using that term "random motion". It's a term used in chemistry (also called Brownian motion), not astronomy...

 

 

I agree that the state of the early universe will have determined where stuff is moving now.

 

Hope I didn't confuse things too much with my analogy with molecules.

 

No don't get me wrong - I totally see where you are coming from, and my first thoughts were why don't the same models apply on the super-scale macro as on the small-scale micro. But on the small scale we can introduce energy via heating up a gas - whereas we cannot introduce energy on the large scale (well couldn't till dark energy). There is a complexity on the small scale that we can, and have to, ignore on the larger scale; the number of interaction of an object in a gas are myriad, the interactions of a cluster (taken as an individual object) are possibly zero. If you are to model the universal expansion through parallel to the molecular world I think you have to consider a system that is minutely above abs zero - it's slow, boring, and can still be modelled with billard balls!

[David Levy]

By Wikipedia: "The Andromeda Galaxy is a spiral galaxy approximately 2.5 million light-years(2.4×10¹⁹ km) from Earth".

 

"The Andromeda Galaxy is approaching the Milky Way at about 100 to 140 kilometres per second (62 to 87 mi/s) (400lightyears every million years),^[66] making it one of the few blueshifted galaxies. The Andromeda Galaxy and the Milky Way are thus expected to collidein about 4.5 billion years"

 

Andromeda is expected to collide with the Milky Way galaxy in about 4.5 Billion year. Where was it 4.5 Billion year ago? We might estimate that as it keeps the speed and direction, it was 5 million light years from Earth. So as we go farther in thepast, it should be farther from Earth. Therefore, 13.5 Billion years ago it was about 7.5 million light years away.

 

Why big bang? Wikipedia: "If the distance between galaxy clusters is increasing today, everything must have been closer together in the past".

 

So, why the science takes it for granted that if the distance between clusters is increasing today, then in the past it must have been closer. But they don't except the idea that if the distance between clusters is decreasing today, then in the past it was much farther…

 

Now they try to convince us that the it didn't work dueto gravity power : imatfaal:" "Andromeda and the Milky Way are actually quite close to each other! And yes, you are correctly they are gravitationally bound and will stay together, and even get closer"

 

So, we all know, that all the mass of the univers was close together after the big bang. Actually it was very very close… so why the gravity power at that time didn't keep all the mass in the same spot???

 

If the gravity power works, then all the mass should be kept together. If it didn't work, then, in the expected time of the big bang,the distance between the two galaxies was over 7.5 million light years away.

 

Hence, it is clear evidence, that there was no Big Bang!!!

 

 

Edited August 24, 2012 by David Levy

[alpha2cen]

So, we all know, that all the mass of the univers was close together after the big bang. Actually it was very very close… so why the gravity power at that time didn't keep all the mass in the same spot???

 

If the gravity power works, then all the mass should be kept together. If it didn't work, then, in the expected time of the big bang,the distance between the two galaxies was over 7.5 million light years away.

 

Hence, it is clear evidence, that there was no Big Bang!!!

 

 

 

This diagram has some difference what you said.

http://en.wikipedia....300_no_WMAP.jpg

I do not know this diagram exactly describe Big Bang, but the diagram has difference what you said.

Expansion and accelerated expansion energy term is curious.

At the cooling state after inflation only kinetic energy term is active?

Many discussion might be done before. But...?

Are we on Big Bang state?

Or

How about Higgs potential decrease with time, or gravity decrease?

The conclusion might be clear after many research.

Edited August 24, 2012 by alpha2cen

[ACG52]

So, why the science takes it for granted that if the distance between clusters is increasing today, then in the past it must have been closer.

 

Well if things are moving apart, then if you reverse the arrow of time, things are closer than they are now.

 

But they don't except the idea that if the distance between clusters is decreasing today, then in the past it was much farther…

 

 

Because the distances between clusters is not decreasing today.

 

Now they try to convince us that the it didn't work dueto gravity power : imatfaal:" "Andromeda and the Milky Way are actually quite close to each other! And yes, you are correctly they are gravitationally bound and will stay together, and even get closer"

 

 

Yes, gravity is stronger than the expansion up to distances of 200 million lys. The Virgo supercluster, which includes both Andromeda and the Milky Way, is gravitationally bound.

 

So, we all know, that all the mass of the univers was close together after the big bang. Actually it was very very close… so why the gravity power at that time didn't keep all the mass in the same spot???

 

 

Because the initial inflationary impulse was far higher than it is today.

 

Why do you post on a topic which you have no knowledge of?

Edited August 25, 2012 by ACG52

[EMField]

Well if things are moving apart, then if you reverse the arrow of time, things are closer than they are now.

 

 

 

Because the distances between clusters is not decreasing today.

 

 

 

Yes, gravity is stronger than the expansion up to distances of 200 million lys. The Virgo supercluster, which includes both Andromeda and the Milky Way, is gravitationally bound.

 

 

 

Because the initial inflationary impulse was far higher than it is today.

 

Why do you post on a topic which you have no knowledge of?

 

 

I don't think anyone knows what gravity or energy is, if you do please explain what causes them for me?

[alpha2cen]

This diagram has some difference what you said.

http://en.wikipedia....300_no_WMAP.jpg

I do not know this diagram exactly describe Big Bang, but the diagram has difference what you said.

Expansion and accelerated expansion energy term is curious.

At the cooling state after inflation only kinetic energy term is active?

Many discussion might be done before. But...?

Are we on Big Bang state?

Or

How about Higgs potential decrease with time, or gravity decrease?

The conclusion might be clear after many research.

 

About Dark Energy

 

Current theory

1) Big Bang theory + Dark Energy

2) Steady state theory

3) Parallel University

4) Holographic Universe

5) Others

 

How about this candidate?

1) On Big Bang theory

2) Higg potential decrease + Big Bang theory

3) Gravity decrease + Big Bang theory

4) The Universe rotates after Big Bang or inflation + Higgs potential or gravity decrease. (Big Bang + Universe rotation + Higgs or gravity decrease)

5) Big Bang + External Universe pressure against the expansion is decreasing

6) Others

 

Which one is correct?

Edited August 25, 2012 by alpha2cen