Why is it customary to assume that the vacuum energy contribution is neglible?

In summary: I?)In summary, the vacuum's energy is thought to be greater than what is accounted for by normal matter, and this has been a mystery for physicists. In the context of general relativity, the vacuum's energy is thought to be the dark energy that is driving the accelerating expansion of the universe. However, this theory has not been able to explain why the vacuum's energy is so much greater than what is accounted for by normal matter.
  • #1
Galteeth
69
1
This is a question from a non-physicist. Since there is much more observed gravity then accounted for by normal matter, why do renormalization methods remove all of the vacuum's energy? I get that the infinite values make no sense, but why assume it's zero?
 
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  • #2
It might be (or might not be) that vacuum energy is the dark energy that drives the accelerating expansion of the universe. This would put (observationally) the vacuum energy at about 10^(-9) J m^(-3), but nobody knows how to get this number from theory.
 
  • #3
past calculations have shown vacuum energy expected to be about 10^120 greater than this figure. Even correcting for supersymmetry the result is still 10^60 too big.
this is the worst result in magnitude for any theory vs observation in physics.

In past years Robt Forward and Feinman both stated that the vacuum energy in a coffee cup could boil the seas. They must have been working from the calculated figure.
 
  • #4
map19 said:
past calculations have shown vacuum energy expected to be about 10^120 greater than this figure. Even correcting for supersymmetry the result is still 10^60 too big.
this is the worst result in magnitude for any theory vs observation in physics.

In past years Robt Forward and Feinman both stated that the vacuum energy in a coffee cup could boil the seas. They must have been working from the calculated figure.

When you say "greater then this figure" what figure are you referring to?
 
  • #5
The figure given by george Jones in the previous post for the observable vacuum energy.
 
  • #6
map19 said:
The figure given by george Jones in the previous post for the observable vacuum energy.

Huh. But I still don't understand why it's more likely to be zero?
 
  • #7
Galteeth said:
Huh. But I still don't understand why it's more likely to be zero?
The basic idea is that physicists don't like small numbers. The argument goes like so: if you have some theory that allows a continuum range of values for the cosmological constant, then it's going to be extraordinarily unlikely that the particular value it chooses will be either close to zero or to some other specific number. Physicists generally expect that it's going to be vastly more likely for it to be forced to be identically zero due to some symmetry or other. However, no such symmetry has been found.

In any case what it means is that the number we see for the cosmological constant is thought unlikely to be an accident, and must take the value it does for a particular reason.
 
  • #8
"Huh. But I still don't understand why it's more likely to be zero?"

me either. It's not zero, and that shows in many different ways.
But is the dark energy, vacuum energy, casimir energy, driving the expansion ? If not, what is ?
here's a thought
When Einstein added a cosmological constant to his equation G(uv) = 8*Pi*GT(uv) he added it on the left-hand side to make the cosmos static. G(uv) + Ag(uv) = 8*Pi*GT(uv) because he thought it was a property of space.
If we accept that the vacuum contains energy the term should be on the right, as follows: G(uv) = 8*Pi*G(T(uv) + P(vac)g(uv)).
 
  • #9
map19 said:
"Huh. But I still don't understand why it's more likely to be zero?"

me either. It's not zero, and that shows in many different ways.
But is the dark energy, vacuum energy, casimir energy, driving the expansion ? If not, what is ?
here's a thought
When Einstein added a cosmological constant to his equation G(uv) = 8*Pi*GT(uv) he added it on the left-hand side to make the cosmos static. G(uv) + Ag(uv) = 8*Pi*GT(uv) because he thought it was a property of space.
If we accept that the vacuum contains energy the term should be on the right, as follows: G(uv) = 8*Pi*G(T(uv) + P(vac)g(uv)).

So general relativity predicts an expanding universe, but the rate of this expansion is accelerating, which is not predicted by GR?
 
  • #10
Galteeth said:
So general relativity predicts an expanding universe, but the rate of this expansion is accelerating, which is not predicted by GR?
GR only predicts how the rate of expansion (or contraction) is related to the contents of the universe. It neither predicts nor forbids accelerated expansion.
 
  • #11
Chalnoth said:
GR only predicts how the rate of expansion (or contraction) is related to the contents of the universe. It neither predicts nor forbids accelerated expansion.

Ok. I know I am out of my league here, but i was always a bit confused by the way our understanding of gravity is presented. I had read that it was "mysterius" why gravity as a force was so weak and that one of the appeals of string theory was that it could explain this by having some of the gravity "leak" into other dimensions, yet on the other hand we have this mystery where there is much more gravity then known matter seems to account for. (I know these two things are not related, it just seems weird on a surface level.)
 
  • #12
You don't use just matter to account for gravitation. Any energy produces gravitation. In General Relativity it's the energy tensor. So you add the effect of mass-equivalent energy, heat, momentum, electromagnetic radiation, dark energy(whatever that is) and any other energy I haven't mentioned, to come up with a total.
Note that other dimensions are speculative, we don't have an experiment to show them.
 
  • #13
map19 said:
You don't use just matter to account for gravitation.
Well, energy is a property of matter. It isn't something that exists in and of itself. And it's not just energy, but also pressure, momentum, and anisotropic shears that affect gravitation.
 
  • #14
Galteeth said:
Ok. I know I am out of my league here, but i was always a bit confused by the way our understanding of gravity is presented. I had read that it was "mysterius" why gravity as a force was so weak and that one of the appeals of string theory was that it could explain this by having some of the gravity "leak" into other dimensions, yet on the other hand we have this mystery where there is much more gravity then known matter seems to account for. (I know these two things are not related, it just seems weird on a surface level.)

I suspect when the reason for gravity is known you won't need such elaborate explanations "as leaking from one dimension to another"...the value of G is in the magnitude of c^2/R which is an estimate quoted by L Smolin (The Trouble with Physics) of the present rate of cosmic acceleration.
 

1. Why is it important to consider the vacuum energy contribution in scientific research?

The vacuum energy contribution is a key factor in understanding the behavior of quantum fields and their interactions. It is important to consider this contribution in scientific research because it can have significant effects on various physical phenomena, such as the expansion of the universe and the Casimir effect.

2. Why is it customary to assume that the vacuum energy contribution is negligible?

The vacuum energy contribution is often assumed to be negligible because, in most cases, its effects are very small compared to other energy contributions. This allows for simpler calculations and models in scientific research. However, in certain scenarios, such as in cosmological models, the vacuum energy contribution cannot be ignored.

3. What is the origin of vacuum energy contribution?

The origin of vacuum energy contribution is still a topic of debate in the scientific community. Some theories suggest that it is a result of the inherent fluctuations of quantum fields, while others propose that it is related to the properties of space itself. Further research and experiments are needed to fully understand its origin.

4. Can the vacuum energy contribution be measured or observed?

Currently, there is no direct way to measure or observe the vacuum energy contribution. However, its effects can be indirectly observed through various physical phenomena, such as the Casimir effect, which is a manifestation of the vacuum energy contribution between two closely spaced objects.

5. How does the vacuum energy contribution affect our understanding of the universe?

The vacuum energy contribution plays a significant role in our understanding of the universe, particularly in cosmology. It is believed to be one of the driving forces behind the accelerated expansion of the universe and can also affect the formation and evolution of structures in the universe. By studying the vacuum energy contribution, we can gain a deeper understanding of the fundamental laws and principles that govern our universe.

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