Perpetual Student
Illuminator
- Joined
- Jul 8, 2008
- Messages
- 4,852
Thanks. I need to review de Sitter space to understand part of your response.Did you read the example with the "string" I gave earlier? That's one way it can happen (that's how vacuum energy arises in quantum field theory). But in this case the physics is simpler. In non-gravitational physics, the absolute value of the energy doesn't mean anything - only energy differences matter, so if you shift every energy by a constant nothing changes. But gravity acts on all forms of energy, even constants - so the absolute value does matter. A scalar potential when the scalar is homogeneous and constant is precisely just that - an overall shift of the energy. Gravity acts on it, and the solution is either de Sitter or anti de Sitter space, depending on the sign (and if there's no other energy around).
It's worth noting that the expansion of space is not a very well-defined concept. In fact in de Sitter and anti de Sitter the space can either be thought of as expanding, contracting, or static - that's a choice of coordinates. Physically the effect of the vacuum energy is to either pull everything in or push it out - and it's perfectly valid to think of that as a force and the space itself as static. Thought of that way, there's no expansion to dilute the energy density.
In that language, inflation is not an exponential expansion of space - it's just a pressure that forces everything to move away from everything else and dilute (though the fact that space is static does not mean it isn't curved - it is - and that's one reason it's possible to keep pushing things without running out of "room").
If you have any math background, I'll give you one more way to think about this. Imagine a sphere. Spheres have constant scalar curvature, and think of that curvature as an energy density (it's directly related to it by Einstein's equations). Now take one of the directions of the space the sphere is in and turn it into time (mathematically, multiply that coordinate by i). That turns the sphere into a hyperboloid (write the equation, multiply by i, and you'll see why). So now the sphere is expanding - exponentially, actually, in this coordinate - but the curvature is still constant.
...
Yes - the energy in the Higgs condensate acts in a way that's nearly identical to the inflaton background.
...
A constant value of the Higgs field is all that's meant by the "Higgs condensate".
OK, easily done -- multiplying one of the coordinates for a sphere turns it into a hyperboloid and the curvature is constant as we move along the "transformed" coordinate to infinity. Is this an analogy or is there an actual equation for energy density that is mathematically structured this way?
Do you refer to the "constant value" (consequently "condensate") of the Higgs field because the Higgs particles are spread out throughout space (due to quantum uncertainty) as you once described to me?
