Zero-Energy Universe Hypothesis: Questions & Answers

In summary: I'm not really sure how to describe it. In any case, I don't think that there is any "corresponding negative potential gravity" that exists to counteract dark energy--it's just a weird property of dark energy that we happen to have named it that.
  • #1
DiracPool
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I ran a search and didn't see anything posted recently, at least, on the current thoughts behind the zero-energy universe idea.

http://en.wikipedia.org/wiki/Zero-energy_universe

The zero-energy universe hypothesis states that the total amount of energy in the universe is exactly zero: its amount of positive energy in the form of matter is exactly canceled out by its negative energy in the form of gravity

I had a few questions about this:

1) What is the opinion of people on this site of the validity of this idea in general?

2) The positive energy in the form of matter is supposed to be exactly or nearly exactly canceled out by the negative potential energy in the form of gravity. What about electrical potential energy though, doesn't this also factor in? If not, why?

And

3) I read somewhere that observationally, the 3-d metric of space is found to be very close to flat, which supports the zero-energy model, but the 4-d metric is supposed to be curved. Is this true? Does this refer to perhaps a negative curvature of Minkowski spacetime? How does that play into the zero-energy universe model and, also, how is dark energy supposed to fit in?
 
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  • #2
DiracPool said:
What is the opinion of people on this site of the validity of this idea in general?

I think it depends on a particular definition of "energy", which has issues; in fact, *any* definition of the term "energy" that tries to give it a global meaning (which this one does) has issues in GR. In certain spacetimes, the issues can be resolved in a fairly reasonable way; but the spacetime that describes the universe as a whole is not such a spacetime (the main reason is that the universe is expanding).

DiracPool said:
What about electrical potential energy though, doesn't this also factor in?

It's part of the "positive energy in the form of matter"; "matter" in this particular case includes radiation, EM fields, etc.--basically anything that isn't gravity.

DiracPool said:
I read somewhere that observationally, the 3-d metric of space is found to be very close to flat

Yes; more precisely, it is found to *be* flat to within the accuracy of our current observations. But note that this depends on how we choose to slice up spacetime into space and time: see below.

DiracPool said:
which supports the zero-energy model

Not really; you can construct a "zero energy" model of the universe regardless of its spatial curvature.

Also, the curvature of 3-d spatial slices depends on how you "cut" them out of 4-d spacetime. The slices that are found to be flat, to within the accuracy of our current observations, are slices cut in a particular way that makes the universe appear homogeneous and isotropic. There are good reasons why we use this particular slicing in our models, but that doesn't change the fact that other slicings, with non-flat spatial slices, are possible.

DiracPool said:
the 4-d metric is supposed to be curved. Is this true?

Yes. *Any* 4-d spacetime that has matter (in the general sense I referred to above) present *must* be curved, by the Einstein Field Equation.

DiracPool said:
Does this refer to perhaps a negative curvature of Minkowski spacetime?

No, because there is no such thing as "negative curvature of Minkowski spacetime". Minkowski spacetime is flat (4-d flat), by definition: that's what "Minkowski spacetime" *means*.

DiracPool said:
How does that play into the zero-energy universe model

It doesn't, really; as I noted above, any 4-d spacetime that has matter present must be curved (4-d curved).

DiracPool said:
how is dark energy supposed to fit in?

Dark energy is basically treated as a kind of "matter" (in the generalized sense I gave above), which happens to have some peculiar properties not shared by other kinds of "matter". This is true in basically any cosmological model, whether it claims to be a "zero energy universe" one or not.
 
  • #3
PeterDonis said:
Dark energy is basically treated as a kind of "matter" (in the generalized sense I gave above), which happens to have some peculiar properties not shared by other kinds of "matter". This is true in basically any cosmological model, whether it claims to be a "zero energy universe" one or not.

Thanks peter, that is exactly what I was looking for. As far as your comment above, does that mean that there is postulated corresponding negative potential gravity that exists to counteract the dark energy as well as "traditional" forms of positive matter-energy? If so, wouldn't that mean that the vast majority of gravitational energy in the universe exists to counter this dark energy?
 
  • #4
DiracPool said:
does that mean that there is postulated corresponding negative potential gravity that exists to counteract the dark energy as well as "traditional" forms of positive matter-energy?

Actually, I'm not sure, because dark energy doesn't produce attractive gravity the way ordinary matter does. I didn't really take that into account in my previous post. :redface: Dark energy still has positive energy density, like ordinary matter does, but unlike ordinary matter, it has negative pressure, which means the net gravitational effect of dark energy (which depends on both energy density and pressure) is repulsive, not attractive.

Taking this into account, I'm not sure that a model including dark energy can have a negative "gravitational potential energy" that offsets the positive dark energy density, the way you can do that for ordinary matter. So I'm not sure there can be a "zero energy universe" model including dark energy. I would need to take some time to look at the math.
 
  • #5


I find the zero-energy universe hypothesis to be a fascinating concept. It is a theory that challenges our understanding of energy and the universe as a whole. While there is still much research and debate surrounding this idea, I can offer some insights to your questions based on current scientific knowledge.

1) The validity of the zero-energy universe hypothesis is still a topic of debate among scientists. There are some who support this idea and see evidence for it in observations, while others argue that it is still too early to make such a claim. More research and observations are needed to fully understand the energy balance of the universe.

2) In the zero-energy universe model, it is believed that all forms of energy, including electrical potential energy, are canceled out by the negative energy of gravity. This is based on the principle of conservation of energy, which states that energy cannot be created or destroyed, only transformed. Therefore, any excess energy in one form must be balanced out by an equal amount of negative energy in another form. However, there is ongoing research to better understand the role of electrical potential energy in the overall energy balance of the universe.

3) The 3-D metric of space refers to the spatial dimensions of length, width, and height, while the 4-D metric includes the dimension of time. The observed flatness of the 3-D metric supports the zero-energy universe model, as it suggests that the total energy of the universe is indeed balanced. However, the curvature of the 4-D metric does not necessarily contradict this idea, as it is believed to be caused by the presence of matter and energy. As for dark energy, it is still a mystery and its role in the zero-energy universe model is still being studied.

In conclusion, the zero-energy universe hypothesis is a complex and intriguing concept that requires further research and observations to fully understand. It challenges our current understanding of energy and the universe, and scientists are actively working to unravel its mysteries.
 

1. What is the Zero-Energy Universe Hypothesis?

The Zero-Energy Universe Hypothesis proposes that the total energy of the universe is exactly zero. This means that the positive energy of matter is balanced out by the negative energy of gravitational attraction and expansion.

2. How does this hypothesis explain the expansion of the universe?

The hypothesis suggests that the universe is expanding due to the repulsive force of dark energy, which counteracts the attractive force of gravity. This expansion is believed to be accelerating, leading to the eventual heat death of the universe.

3. Is there any evidence to support the Zero-Energy Universe Hypothesis?

While there is no direct evidence, the hypothesis is consistent with current observations of the universe, such as the flatness of the universe and the observed acceleration of expansion. However, more research and evidence is needed to fully support this hypothesis.

4. How does this hypothesis relate to the Big Bang Theory?

The Zero-Energy Universe Hypothesis is a modification of the Big Bang Theory. It suggests that the universe began with a singularity and has been expanding ever since, but the total energy remains at zero. This differs from the traditional Big Bang Theory, which assumes a non-zero total energy of the universe.

5. What implications does this hypothesis have for the future of the universe?

If the Zero-Energy Universe Hypothesis is correct, it means that the universe will continue to expand and eventually reach a state of maximum entropy, known as the heat death of the universe. This would result in a universe with no energy or activity, effectively leading to the end of all life and processes as we know them.

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