pressure and the universe?

[Boratssister]

could the pressure of the universe explain the expansion of the universe ? I was daydreaming when I considered atmospheric pressure and how the energy of the atoms creates the pressure. Then I took the gravity away and all the atmosphere then expanded . Then I wondered whether the expansion of the universe worked in the same way?May be galaxys and blackholes solar winds are responsible for this, that is if galaxys have a kind of solar wind?
Forgive me if this is ridiculous or has been covered before. I posted this on a whim.

[Cougar]

Even when great leaps of [scientific] progress do occur, they only rarely come "out of the blue." Advances are nearly always preceded by years, decades, or even centuries of patient accumulation of facts and data and ideas." [Rocky Kolb, Blind Watchers of the Sky]

[Jeff Root]

To expand on Cougar's excellent answer, pressure was probably the first
thing that astronomers thought of as the initial cause of the expansion
when it was realized back in 1929 or threabouts that everything must
have started out all squished together in one place. But they quickly saw
that pressure couldn't do it. The farther apart two galaxies are, the faster
they are moving away from each other. That wouldn't happen if pressure
were the cause.

-- Jeff, in Minneapolis

[Boratssister]

To expand on Cougar's excellent answer, pressure was probably the first
thing that astronomers thought of as the initial cause of the expansion
when it was realized back in 1929 or threabouts that everything must
have started out all squished together in one place. But they quickly saw
that pressure couldn't do it. The farther apart two galaxies are, the faster
they are moving away from each other. That wouldn't happen if pressure
were the cause.

-- Jeff, in Minneapolis

Thankyou for your thoughts, the universe can be counter intuitive ! 2 galaxies at opposite sides of our visible universe are moving away from each other faster than galaxies in the centre! Strange! I see , if pressure was the explanation, a kind of brownian motion would be observed. That is to say that galaxies would be random in there motions,? Is there some kind of gravitational pull at the edge of the universe causing the acceleration of far out galaxies?

[DrWho]

Is there some kind of gravitational pull at the edge of the universe causing the acceleration of far out galaxies?
Possibly - see this reference on Dark Flow (http://en.wikipedia.org/wiki/Dark_flow). However, this appears to be an anomolous movement in a particular direction. But in general, the universe is expanding (and accelerating) uniformly in all directions due to a repulsive force labeled as Dark Energy (http://en.wikipedia.org/wiki/Dark_Energy).

[Jeff Root]

No, there is nothing pulling at any edge or edges. The conventional
wisdom is that the Universe doesn't even have any edge. It may be
finite or it may be infinite, but even if it is finite, there might not be
anyplace that is significantly different from the way things are right
here where we are: On the largest scales, the Universe seems to look
pretty much the same in every direction, nomatter where you are
located.

It is possible for an infinite volume of particles to move farther and
farther apart from one another in the same way as the cosmic expansion,
but it is clear to me that everything that is participating in the expansion
had to be in causal contact at the beginning, so I don't believe it can be
infinite. Measurements suggest that the overall geometry of the Universe
may be "flat", so I can't understand how it could be finite but without an
edge. If the Universe has overall curvature, it can be closed, in which
case it would have no edge, in very much the same way that the surface
of the Earth has no edge: You can keep going in any direction and never
come to the edge of the Earth's surface.

The cause of initial expansion is unknown, the cause of Inflation-- which
is a hypothesized extremely brief, fast, and large expansion event that
might have occurred when the Universe was a tiny fraction of a second
old-- is also unknown, and the cause of the current acceleration of the
expansion-- which has apparently been going on for the last few billion
years, after a period of slowing during the first several billion years of
the Universe's existence-- is ALSO unknown. The cause of the slowing
would be the mutual gravitational atttraction of all the matter in the
Universe for all the other matter.

-- Jeff, in Minneapolis

[Spaceman Spiff]

Note the presence of the pressure term (lower case 'p') in the second of the Friedmann Equations (http://en.wikipedia.org/wiki/Friedmann_equations#The_equations). If the matter is far from relativistic (pc << mc2, where here p is the momentum), then the pressure is also much less than the rho*c2 term. Such universes are called 'pressureless'. In the present universe, both matter and radiation have small pressure terms relative to the matter's contribution to the rho*c2 term.

This situation has not always been true. The early universe was radiation dominated, and radiation pressure dominated. However, positive pressures (such as those from radiation and matter) contribute attractively to gravitation, perhaps contrary to what one might have guessed.

[astromark]

No, there is nothing pulling at any edge or edges. The conventional
wisdom is that the Universe doesn't even have any edge. It may be
finite or it may be infinite, but even if it is finite, there might not be
anyplace that is significantly different from the way things are right
here where we are: On the largest scales, the Universe seems to look
pretty much the same in every direction, nomatter where you are
located.

It is possible for an infinite volume of particles to move farther and
farther apart from one another in the same way as the cosmic expansion,
but it is clear to me that everything that is participating in the expansion
had to be in causal contact at the beginning, so I don't believe it can be
infinite. Measurements suggest that the overall geometry of the Universe
may be "flat", so I can't understand how it could be finite but without an
edge. If the Universe has overall curvature, it can be closed, in which
case it would have no edge, in very much the same way that the surface
of the Earth has no edge: You can keep going in any direction and never
come to the edge of the Earth's surface.

The cause of initial expansion is unknown, the cause of Inflation-- which
is a hypothesized extremely brief, fast, and large expansion event that
might have occurred when the Universe was a tiny fraction of a second
old-- is also unknown, and the cause of the current acceleration of the
expansion-- which has apparently been going on for the last few billion
years, after a period of slowing during the first several billion years of
the Universe's existence-- is ALSO unknown. The cause of the slowing
would be the mutual gravitational atttraction of all the matter in the
Universe for all the other matter.

-- Jeff, in Minneapolis

That post has said what we know of and can say about this and a number of other threads in this forum... re read it. Take it in, and understand its magnitude... thank you Jeff.

[DrWho]

No, there is nothing pulling at any edge or edges. The conventional wisdom is that the Universe doesn't even have any edge.
There may not be an edge in the conventional meaning of the word, but one can say that a moving edge of observability exists. And if there's nothing pulling beyond the edge of observability, then what is causing the directional movement of galaxy clusters (over a span of 5 Gly), dubbed the dark flow?

[astromark]

Help me to understand your question... Your Dark Flow is the direct action of the force Dark Energy. The answer being we do not know why or what that is. But we do now that it is.

[DrWho]

Help me to understand your question... Your Dark Flow is the direct action of the force Dark Energy. The answer being we do not know why or what that is. But we do now that it is.
Dark flow is unrelated to dark energy. Follow the link I posted earlier to find out more.

[astromark]

Yes, having read the link I see your confusion, not mine.:)
That report is unspecific and having searched out the actual papers have found little reason to change my view. The background cosmic noise as a remnant of the BB is a reference point for the measurement of expansion. Insufficient time has elapsed to make a meaningful evaluation as yet. Far more data is required before a decisive conclusion could be drawn. Thus far its all to easy to jump to unfounded conclusions. I will wait.

[DrWho]

Yes, having read the link I see your confusion, not mine.:)
Why do you think I'm confused?


That report is unspecific and having searched out the actual papers have found little reason to change my view.
Which papers have you read (the paper I read was quite specific) and what is your view?


The background cosmic noise as a remnant of the BB is a reference point for the measurement of expansion. Insufficient time has elapsed to make a meaningful evaluation as yet.
Insufficient time for what?


Far more data is required before a decisive conclusion could be drawn. Thus far its all to easy to jump to unfounded conclusions. I will wait.
Yes, more information is always welcome. However, the results do seem to indicate that something is going on, so the conclusions are founded on observational evidence.

[astromark]

Why... because you said this, ' Dark flow is unrelated to dark energy.' I do not agree. However do not let my opinion challenge your enthusiasm to explain. You also ask where and what is my view... where,? on the net. I hit the search key. and read. Its not compulsory to except.
My view,? I try not to be to quick with a my view... I want more decisive information. and that is what I will wait for. If you think I am wrong to stick to my more uniform expansion of a lumpy universe view, that's fine with me... As being wrong is a art form I seem to have mastered. It comes as no shock to me that you think I am confused...I often am. I thrive on it. I just want more of your observational evidence confirmed as fact. Not arm waving... I am seeing a lot of that.

[DrWho]

Why... because you said this, ' Dark flow is unrelated to dark energy.' I do not agree.
Well, it isn't. It's a specific effect affecting a specific cluster of galaxies. I'm not saying that the results haven't been challenged (they have, and have been defended) and that further measurements won't provide a better understanding of the observed phenomenon (the paper is only a year old). But one thing is clear, if the effect is real, then it cannot be down to what we understand as dark energy (which applies uniformly).

[astromark]

That there are fluctuations of the rate at which we observe the expansion I understand and agree. I would expect it. Gravatational clumping and clusters of galaxies are bound to influence the rate of movment. I know so little of dark mater, dark energy and now dark flow...Gravatational attraction at a galactic level may never be part of human experience so does it matter so much... to argue the point is just plain silly. We obviously understand and comprehend what we read. The manner and method of expression is the issue., and if you except it.
You seem to have forgotten the question; Re the OP. That the universe is expanding we have no doubt. Why and by what mechanism is the question as yet unanswered... mark.

[DrWho]

Gravatational clumping and clusters of galaxies are bound to influence the rate of movment.
Galactic motion has nothing to do with the expansion of space.


I know so little of dark mater, dark energy and now dark flow...
Agreed.


Gravatational attraction at a galactic level may never be part of human experience so does it matter so much... to argue the point is just plain silly.
What's plain silly is that comment. We have an excellent understanding of gravitational attraction both at the galactic level and the local level, so it is very much a part of our experience. And even if it were not, you're saying it's silly to inquire about it? The workings of quantum mechanics is beyond human experience and yet according to your logic, it would have been silly to look into it!


We obviously understand and comprehend what we read. The manner and method of expression is the issue., and if you except it.
Huh?


You seem to have forgotten the question; Re the OP. That the universe is expanding we have no doubt. Why and by what mechanism is the question as yet unanswered.
You seem to have difficulty following the chain of reasoning in an extended conversation.

[astromark]

You have done it again.... you said ' Galactic motion has nothing to do with the expansion of space' and that is wrong. Objects of mass that are not gravationaly bound are moving away. Yes its said that it is space itself that is expanding. Do you not see this,? As for your 'Huh?' and 'Agreed'... you are being interpreted as hostile. Stop it.
I am well up to a conversation. But I think you must concede some facts as yet are not all so clear. I have looked back through this thread and want to help those whom ask... You tell me what is pulling the universe apart and by what force that is applied,? Remember the question...

[DrWho]

You have done it again.... you said ' Galactic motion has nothing to do with the expansion of space' and that is wrong.
How is it wrong? You are mistaken. Do you expect that distant galaxies are moving through space at near lightspeed and faster? No, the galaxies themselves move at very modest speeds through space relative to CMB. It's the space between the galaxies that is expanding rapidly, at larger scales.


Objects of mass that are not gravationaly bound are moving away. Yes its said that it is space itself that is expanding. Do you not see this,?
I do, which is why it's incorrect to say that galactic recession is due to the movement of galaxies rather than cosmic expansion of the space between them.


As for your 'Huh?' and 'Agreed'... you are being interpreted as hostile. Stop it.
Well, I had no idea what you meant to say there and that was my first reaction. Should I have ignored it?


I am well up to a conversation. But I think you must concede some facts as yet are not all so clear.
Then why not ask for clarification? I respond to 'Huh?' queries.


You tell me what is pulling the universe apart and by what force that is applied,? Remember the question...
Whose question? The OP question about whether pressure is causing the expansion has been answered. The follow up question was about whether there is some gravitational pull at the edge of the universe, I responded with some recent findings dubbed the dark flow. Standard dark energy isn't an 'edge' effect, it applies to all of space. So what question are you talking about?

[philipi]

I don't think energy, or plasma, or gas in interstellar space behaves according to Boyles Law for Gases. Boyle's Law is operative in Earth's atmosphere, or at the very least in the gravity well of a planet.

It would be great if an astronomer or physicist weighed in on this.

Here's a wiki
http://en.wikipedia.org/wiki/Boyle%27s_law

[Boratssister]

Thankyou jeff and other contributers. I hope humans are able to answer these problems. The sort of gravitational forces I was referring to was the blackhole hole kind. Would our visible universe falling into a giant black hole which is bigger than our universe explain the accelerating galaxys and the red shift and the background radiation. Forgive me , I make answers up when I don't know......

[DrWho]

Would our visible universe falling into a giant black hole which is bigger than our universe explain the accelerating galaxys and the red shift and the background radiation.
No. Galaxies are receding in all directions from our vantage point and from every other galaxy's vantage point (rather than a bulk movement in a single direction).

[Boratssister]

No. Galaxies are receding in all directions from our vantage point and from every other galaxy's vantage point (rather than a bulk movement in a single direction).

In theory then no galaxys should collide? Or clusters of galaxys should not collide? Are any clusters of galaxys colliding ?

[DrWho]

In theory then no galaxys should collide?
Not quite true. Galaxies that are close enough to be gravitationally bound can and do collide because their mutual attraction overcomes spatial expansion.


Or clusters of galaxys should not collide? Are any clusters of galaxys colliding ?
Yes, galaxy clusters can collide for the same reason. In fact we (the local group) will likely collide with the Virgo cluster.

[Boratssister]

Not quite true. Galaxies that are close enough to be gravitationally bound can and do collide because their mutual attraction overcomes spatial expansion.


Yes, galaxy clusters can collide for the same reason. In fact we (the local group) will likely collide with the Virgo cluster.

So is it is safe to say, that all galaxys are accelerating away from each other appart form those galaxys whoms gravity forbids this.... It seems I need to understand gravity a bit better. Thankyou Drwho!

[Jeff Root]

Things that are very far apart are generally moving farther apart. Things
that are near each other are generally gravitationally bound to each other,
or at least to the same collection of stuff. Things that are much more than
10 million light-years apart are almost always moving away from each other.
Things that are much less than a million light-years apart are almost always
gravitationally bound to the same galaxy or group of galaxies.

Everything must have started out in the Big Bang as a hot gas, as you
assumed. Although the pressure idea doesn't work (at least, not by itself),
the hot gas part is correct. The gas expanded and cooled to the point that
the mutual gravitation of regions with greater than average density could
start to hold the gas together. Bunching appears to have occurred mainly
at three levels: stars-- where the atoms collide with one another and
interact via friction as well as gravity; galaxies-- where stars exchange
gravitational potential energy and kinetic energy with one another; and
clusters of galaxies, where the large distances involved means that not a
whole lot has had time to happen beyond simple gravitational attraction.
Of course, galaxies that are not so far apart have had time to collide and
even merge. The evidence so far seems to suggest that the bunching
occurred at all levels at approximately the same time, or that it began at
the largest scales first, with the gas separating into regions which would
eventually become clusters of galaxies; those regions then clumped into
regions which would eventually become galaxies, and those regions then
clumped into stars. Currently we see a very important level of clumping
with giant molecular clouds, which can produce hundreds or thousands
of stars. The Orion Nebula is one such. As the name implies, molecular
clouds are home to larger molecules than the simple gases which created
the first generation of stars, so their clumping is different from that which
created the first stars. Generally, they clump more readily.

-- Jeff, in Minneapolis