Conservation of energy in cosmology

In summary, according to Sean Carroll energy is not conserved in cosmology anyway, so the claim that the universe came from "nothing" doesn't violate any conservation laws.
  • #1
windy miller
303
25
Models like Vilenkin's tunnelling from nothing model described here:
https://www.sciencedirect.com/science/article/abs/pii/0370269382908668
claim the universe came from "nothing". It is claimed this doesn't violate any conservation laws because the negative energy of gravity and the positive energy of matter can cancel each other out. However according to Sean Carroll energy is not conserved in cosmology anyway ,see here:
http://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/comment-page-2/
So my question is why do people like Vilenkin even worry about whether or not the positive energy of matter is balanced by the negative energy of gravity if energy is not conserved in cosmology?

Note: please let's not get into a phislophical debate as to the meaning of "nothing: here , my question is not about that.
 
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  • #2
Energy of matter alone is not conserved, that's what Carroll is saying. Vilenkin however talks about total energy of matter and gravity together, which is supposed to be conserved. The problem is that the energy of gravity is, in general, not defined uniquely in a covariant way. It can be defined such that the total energy is conserved, but some purists do not take this definition seriously because it's not covariant. For those purists only the matter energy is well defined, which is not conserved.

See also https://www.physicsforums.com/insights/does-gravity-gravitate/ by @PeterDonis .
 
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  • #3
Demystifier said:
Energy of matter alone is not conserved, that's what Carroll is saying. Vilenkin however talks about total energy of matter and gravity together, which is supposed to be conserved. The problem is that the energy of gravity is, in general, not defined uniquely in a covariant way. It can be defined such that the total energy is conserved, but some purists do not take this definition seriously because it's not covariant. For those purists only the matter energy is well defined, which is not conserved.

See also https://www.physicsforums.com/insights/does-gravity-gravitate/ by @PeterDonis .
Ah ok thanks very much , appreciate the reply.
 

Related to Conservation of energy in cosmology

1. What is the conservation of energy in cosmology?

The conservation of energy in cosmology is a fundamental principle that states that energy cannot be created or destroyed, but can only be transformed from one form to another. This applies to the entire universe, including all matter and energy within it.

2. How does the conservation of energy apply to the expanding universe?

In the expanding universe, the conservation of energy still holds true. This means that as the universe expands, the total amount of energy remains constant, but it is spread out over a larger volume. This is known as the conservation of energy density.

3. Does the conservation of energy apply to dark energy and dark matter?

Yes, the conservation of energy applies to all forms of energy, including dark energy and dark matter. These mysterious substances may have different properties and behaviors, but they still follow the fundamental principle of energy conservation.

4. How does the conservation of energy impact the fate of the universe?

The conservation of energy has a significant impact on the fate of the universe. If the total amount of energy in the universe is positive, it will continue to expand forever. If it is negative, the universe will eventually collapse in a "big crunch." Current observations suggest that the universe has a positive energy density and will continue to expand.

5. Are there any exceptions to the conservation of energy in cosmology?

No, the conservation of energy is a universal principle that has been observed and tested in countless experiments and observations. It is a fundamental law of physics and applies to all systems, including the vast and complex universe.

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