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QuantumT

Is gravity really "negative energy"?

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Okay, I just saw this short 3 minute video about our universe coming from nothing.

In it, the narrator says that gravity is the counterpart (negative energy) that balances the universe to a total value of 0 energy. Is that correct?

 

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In general YouTube is a horrible place to try to learn science.  YouTube videos from respected universities are of course fine!

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Is gravity really "negative energy"? No. Gravity is a somewhat nebulous term here. It's an interaction. It's spacetime curvature.

Is gravitational potential energy negative? Yes, by convention. But not AFAIK by anything dictated by nature.

 

The gravitational PE is given by -GMm/r which goes to zero when r becomes infinitely large. So it's very convenient to use this convention. But there is an additive constant, which is assumed to be zero. And everything still works if it has some other value, but that makes the math harder to do. Since it doesn't matter, we use zero.

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34 minutes ago, Bufofrog said:

In general YouTube is a horrible place to try to learn science.  YouTube videos from respected universities are of course fine!

33 minutes ago, swansont said:

Is gravity really "negative energy"? No. Gravity is a somewhat nebulous term here. It's an interaction. It's spacetime curvature.

Is gravitational potential energy negative? Yes, by convention. But not AFAIK by anything dictated by nature.

 

The gravitational PE is given by -GMm/r which goes to zero when r becomes infinitely large. So it's very convenient to use this convention. But there is an additive constant, which is assumed to be zero. And everything still works if it has some other value.

Yeah, I sensed there was something kooky about his claims...

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I wasn't addressing his claim. I was addressing your flawed restatement of it. Can't have a discussion if the original phrasing is botched.

There is discussion of the total energy of the universe being zero. AFAIK, the hypothesis has merit. Everything we do in physics regarding interactions between multiple bodies (or at least almost everything) is in a situation where it depends on the difference of energy, so an additive constant has no impact. IOW, we don't do things that determine an absolute energy of the universe (which of course is frame dependent anyway)

I don't know if a zero-energy universe has been ruled out.

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10 minutes ago, swansont said:

I was addressing your flawed restatement of it.

I'm sorry if I presented it wrong, I didn't intend to. But didn't he say that gravity is the counterpart of matter?

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2 minutes ago, QuantumT said:

I'm sorry if I presented it wrong, I didn't intend to. But didn't he say that gravity is the counterpart of matter?

I don't know. I didn't watch the video. You are supposed to provide the discussion material, so that the video is not necessary.

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36 minutes ago, swansont said:

I don't know. I didn't watch the video.

Then I suppose my presentation is correct. The video is only there, so you can 'see it for yourself'. It is only 3 minutes long.

36 minutes ago, swansont said:

You are supposed to provide the discussion material, so that the video is not necessary.

This is his claim:

claim.thumb.jpg.a41d68a5579f93480b82fb73e2e6d180.jpg

Is that correct?

Edited by QuantumT

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It seems Michio Kaku agrees. He says* the exact same thing.

(* duration 1 minute 16 seconds)

Edited by QuantumT

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The zero energy universe isn't entirely ruled out. The term applies to a treatment where positive matter energy is balanced by negative gravitational potential energy. However this theory only works in Cartesian coordinates and must apply pseudo tensors. Which is frowned upon under GR. There have been some attempts to correct this problem under other coordinate systems however the psuedo tensors are still required.

It is oft also called the Universe from Nothing model as it's oft coined the ultimate free lunch

Edited by Mordred

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12 hours ago, QuantumT said:

Finally I managed to find a description to the claims. It has a name. Zero Energy Universe

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

It's a hypothesis.

I called your attention to the existence of this a few posts back.

16 hours ago, QuantumT said:

Is that correct?

That's the claim. Is the claim correct? We don't know. As Mordred says, it hasn't been ruled out.

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