Negative pressure and dark energy

[relativityfan]

hi,

which phenoma are known in quantum mechanics to cause a repulsive gravity due to negative pressure? as far as i understand, the vacuum energy of the time energy uncertainty has a very low energy density but it should have a positive pressure because it can only push and not pull. am i right?

i would be grateful if you could reply!

 

[Chronos]

Vacuum energy is still on suspect list for sources of the cosmolgical constant. Empirical tests of lamba only require a tiny amount of repulsive energy density in the vacuum. Measuring this energy is another matter. Without some sort of renomalization, calculations indicate vacuum energy should be virtually infinite, which is clearly wrong. The proper method for renormalizing the vacuum energy remains unknown, not to mention a method to measure it.

 

[relativityfan]

but has this vacuum energy a negative pressure? it seems to me that the pressure of this energy is positive and not negative

 

[Chronos]

Agreed. It is believed to have a positive [anti gravity] pressure. The gravitational consequences under GR are, however, unclear.

 

[relativityfan]

very interesting, do you have any reference that demonstrates this? i have never found such information. if we apply GR, then a positive pressure and positive energy density leads to a gravitationnally attractive field, and then this vacuum energy is not compatible with general relativity stating that dark energy has negative pressure, or I am wrong?
I would be grateful to find a reference about this...

 

[TrickyDicky]

very interesting, do you have any reference that demonstrates this? i have never found such information. if we apply GR, then a positive pressure and positive energy density leads to a gravitationnally attractive field, and then this vacuum energy is not compatible with general relativity stating that dark energy has negative pressure, or I am wrong?
I would be grateful to find a reference about this...

Actually, all those supposed properties of lambda are purely speculative,so it's not easy to find references in mainstream science about this, no positive pressure has ever been found in vacuum, what has been experimentally confirmed is that vacuum has negative pressure (atractive) as seen in a phenomenon discovered more than 50 years ago and repeated and checked many times since called the Casimir force or effect, and is also known the energy-stress tensor of empty space has negative pressure in its trace.

 

[relativityfan]

and is also known the energy-stress tensor of empty space has negative pressure in its trace.

really? where did you get that information?

 

[Chronos]

The casimir effect can also be repulsive, depending on geometry. It is, however, more important to note it is not entirely clear the casimir effect is due to vacuum energy. Assuming you have done your homework, relativityfan, you already know this. In fact, I find it highly unlikely anyone who tosses out terms like 'time energy uncertainty' does not. This looks like a troll to me. I am not that easily deceived.

 

[Phrak]

Does dark energy have a rest frame? If so, what is it's stress-energy in Riemann normal coordinates?

 

[TrickyDicky]

really? where did you get that information?

The vacuum energy tensor is Lorentz invariant, so the sign of its trace components has the same sign that the trace of Minkowski metric tensor.

 

[TrickyDicky]

The casimir effect can also be repulsive, depending on geometry. It is, however, more important to note it is not entirely clear the casimir effect is due to vacuum energy.

To the relative extent that most things at this level are clear, I think there is agreement that the casimir effect is due to vacuum energy in the form of a differential in quantized field that give rise to a force, depending on the arrangement of the plates that are used in the experiment it can be atractive or repulsive, but it is usually considered the resultant of a negative pressure.