Negative Pressure

[Aki]

?

[Tormod]

wouldn't that be suction?

 

I found this description on the web;:

 

NEGATIVE PRESSURE: Condition that exists when less air is supplied to a space than is exhausted from the space, so the air pressure within that space is less than that in surrounding areas. Under this condition, if an opening exists, air will flow from surrounding areas into the negatively pressurized space.

 

http://www.ebtron.com/indoor_air_quality/iaq_indoor_air_quality_glossary.htm

[Freethinker]

Originally posted by: Aki

?

The opposite of this post. :-)

[TeleMad]

The original poster may be referring to the negative pressure that caused an expansion of the early universe.

[Aki]

Yeah, I read somewhere about negative pressure a long tim ago, so I don't remember what it was about, but I"m sure it has to do with the expansion of the universe or something like that.

[Aki]

Originally posted by: Tormod

wouldn't that be suction?

 

 

 

 

 

 

 

NEGATIVE PRESSURE: Condition that exists when less air is supplied to a space than is exhausted from the space, so the air pressure within that space is less than that in surrounding areas. Under this condition, if an opening exists, air will flow from surrounding areas into the negatively pressurized space.

 

 

so how does that relate to the expansion of the universe?

[Tormod]

It does not, I had no idea what reference you had in mind when you were asking your question, Aki.

[TeleMad]

Just so you know, I've read about negative pressure and expansion of the Universe in a couple of places, but I don't know the details...so can't help. The only thing I can suggest is searching for keywords: expansion, universe, negative pressure, and tension.

[Aki]

Originally posted by: Tormod

It does not, I had no idea what reference you had in mind when you were asking your question, Aki.

 

Lol, I don't remember myself anymore. I read it in one of the books, it might be in The Elegant Universe, or Hyperspace. But I really don't remember what it was about...

[Bo]

well i've posted several things now on dark energy (maybe someone can assemble the posts?) but here the subject of negative pressure: (as always: i refer to the book of A. Liddle: 'An Introduction to modern cosmology")

 

(things between braces might be a bit technical; skip them if you wish)

In standard Cosmology ALL the matter in the universe is described as a fluid. This means that on the LARGE scale all our planets and stars and solar systems behave like the molecules in a fluid. (of course the interactions are completely different; in a fluid van der waals-bonds and collisions are important; in cosmology Gravity is the only relevant force)

As with the fluid, we can assign a density and a pressure to this 'cosmological' fluid. (note that this pressure doesn't produce any work; because the pressure is everywhere the same).

 

Now it turns out that all normal matter and radiation has a positive pressure. In a way this is equivalent to saying that normal matter has an attractive gravitational force. So slowing the expansion of the universe down.

 

But recent (1998 iirc) measurements showed that the expansion of the present day universe is not slowing down, but speeding up. The 'energy' esponsible for this speeding up is in general called 'dark energy'. And for the dark energy to have the desired properties; it should have a negative pressure.

many ideas on what this dark energy is exist: scalar fields; leaking gravity; Brane collisions.... In other posts i explain those things

 

NB in the normal -non cosmological- sense; Tormod's description of negative pressure is sufficient

 

Bo

[Aki]

what are scalar fields?

 

Is leaking gravity the thing about gravitons can escape to other parallel universe, and therefore gravity is the weakest force?

 

I saw the Elegant Universe episodes, and a brane collision might have caused the big bang, so how does that relate to dark energy?

 

Bo, please tell me more

[Bo]

what are scalar fields?

hmm First of all the question: "What is a field?" Without going into details: a field is in some sense a different way to describe a particle. A classical particle has a certain postion in space. We can specify the particle by specifying the position and the properties of the particle. In quantum mechanics it is a lot harder to talk about exact positions, so one uses to concept of a field. A field is defined over the complete space.

A "scalar field" is a field, with no spin. spin is a (quantummechanical) property of a particle, but this is not really the important point here

The notion of scalar fields in the context of negative pressure is the following: A scalar field, subject to some conditions, can have the properties to drive inflation (the accelerated expansion of the universe) (such a field is commonly called the inflaton field). A nice thing is that such scalar fields, arise very naturally from String theory.

 

Is leaking gravity the thing about gravitons can escape to other parallel universe,....

I wouldn't say 'parallel universe' but 'extradimensional' is the right word. String theory gives the possibility that most 'normal' matter is confined in our 'normal' 4 dimensional space-time, while gravity on the large scale can escape to 5th or higher dimensions, losing it's 'grip' in our 4D world.

 

...and therefore gravity is the weakest force?

No; this has nothing to do with it Even without leaking gravity, gravity is the weakest force.

 

I saw the Elegant Universe episodes, and a brane collision might have caused the big bang, so how does that relate to dark energy?

This is called the ekpyrotic scenario, see another topic

 

Bo

[Aki]

ah, thanks for clarifying things for me Bo.