The energy of the Universe

[geordief]

What might be the overall  energy of the observable universe?

Is it possible that ,to an approximation  it might add up to zero?

 

Since there is a universe beyond what we can observe that may mean we can never know the answer but are there  any models that could be used to answer the question?

 

(Are there as many possible  answers  to the question as there are frames of reference?)

 

 

[MigL]

usually, what one does is set gravitational potential energy as negative, and since it somewhat matches the magnitude of the intrinsic energy of the universe, we can say the universe is net zero energy.
This is the 'universe from nothing' pitched by L Krauss.

See here      Zero-energy universe - Wikipedia

Whether a property can be positive or negative, or simply an 'accounting' trick, or whether it even makes sense to consider energy on a global scale, is for people with better minds than mine to consider.

[zapatos]

On 8/1/2022 at 10:42 AM, geordief said:

Since there is a universe beyond what we can observe...

Hmm. Can you expound on that a bit?

[geordief]

5 minutes ago, zapatos said:

Hmm. Can you expound on that a bit?

Yes

I think it is accepted that ,as the universe expands  galaxies ,one by one will recede from our point of observation  at greater and greater speeds

 

If we look closely enough and long enough I assume  that we will  ,at least in  theory catch one of these galaxies in the process of actually disappearing from view (when its speed of recession exceeds  the speed of light)

 

At that point we will  conclude  that that particular galaxy we no longer see is still there , but no longer as a part of the observable universe

 

Now it would  be a part of the "unobservable universe "-and so "beyond the observable  universe"

We cannot see anything beyond the observable universe but can deduce its existence in an empirical way

 

Does that clarify  what I was saying?

 

(Hope I didn't sound like Mystic Meg in that previous post😀

 

 

 

[zapatos]

16 minutes ago, geordief said:

Does that clarify  what I was saying?

 

Yes, thank you. 😃

[MigL]

By 'set' I mean set the model such that 'gravitational potential is equal in magnitude to the intrinsic energy', so that predictions such as the 'universe from nothing' can be made.

I was not suggesting a 'creator' set the initial conditions in that way, as some have misinterpreted.

My apologies for bad choice of wording.

Edited August 3, 2022 by MigL

[mistermack]

On 8/2/2022 at 4:23 AM, MigL said:

usually, what one does is set gravitational potential energy as negative, and since it somewhat matches the magnitude of the intrinsic energy of the universe, we can say the universe is net zero energy.

Didn't you post elsewhere that energy is frame-dependent? How would that match up with net zero? 

Say you have a bank account with nothing in it, and you borrow £100, then you have £100 in your pocket, and the bank has minus £100, so the net amount is zero. But the bank has to have money from someone else to make the loan.  Maybe the Universe has to have access to the total energy from somewhere else, for what we experience to exist. 

[MigL]

I also said

On 8/1/2022 at 11:23 PM, MigL said:

Whether a property can be positive or negative, or simply an 'accounting' trick, or whether it even makes sense to consider energy on a global scale, is for people with better minds than mine to consider.

 

[joigus]

6 hours ago, mistermack said:

Didn't you post elsewhere that energy is frame-dependent? How would that match up with net zero? 

We live in a De Sitter universe. That means that the universe looks very much the same for every typical observer (galaxy): same horizon distance, same distribution of receding speeds for the galaxies, etc. However you define the energy (sources, geometric terms, vacuum energy) it will be the same for every observer.

It's worth noting though that in general relativity all discussions concerning energy are much more subtle than in classical mechanics.

 

 

Edited August 3, 2022 by joigus
link added

[geordief]

On 8/2/2022 at 4:23 AM, MigL said:

usually, what one does is set gravitational potential energy as negative, and since it somewhat matches the magnitude of the intrinsic energy of the universe, we can say the universe is net zero energy.
This is the 'universe from nothing' pitched by L Krauss.

See here      Zero-energy universe - Wikipedia

Whether a property can be positive or negative, or simply an 'accounting' trick, or whether it even makes sense to consider energy on a global scale, is for people with better minds than mine to consider.

Is the the energy that is bound up in matter (= its mass?) bound up in the form of the various bonds between its constituent  parts?

If so ,is that a bit like Cheshire cat territory where all that was left of the cat was its grin?

 

I think Lewis Caroll was also a foremost mathematician  of his day before falling out of favour for some reason I don't recall.

Edited August 3, 2022 by geordief

[swansont]

55 minutes ago, geordief said:

Is the the energy that is bound up in matter (= its mass?) bound up in the form of the various bonds between its constituent  parts?

If so ,is that a bit like Cheshire cat territory where all that was left of the cat was its grin?

The energy of binding for electrostatic and gravitational interactions is negative, that is, you have to release energy to form a bound system. It’s an energy deficit, as compared to having free particles, so there is no energy bound up in the bonds. 

[geordief]

49 minutes ago, swansont said:

The energy of binding for electrostatic and gravitational interactions is negative, that is, you have to release energy to form a bound system. It’s an energy deficit, as compared to having free particles, so there is no energy bound up in the bonds. 

Is that just a mathematical convention?Could it just as well be the other way round ? (positive energy could be considered negative and vice versa)

 

Or does it have to be that way?

[md65536]

17 hours ago, mistermack said:

Didn't you post elsewhere that energy is frame-dependent? How would that match up with net zero?

You could choose a frame of reference where the entire universe has some great momentum, just by using an observer that's travelling at high speed relative to most stuff. It probably doesn't mean much to give a net momentum to the entire universe (because that's relative to what?). Or you could choose a frame where the universe has no net momentum. If you can do that, you can consider the "invariant energy" of the universe.

Adding to what joigus wrote, I think anywhere you are in the universe you can define an observer where, measured locally, the net momentum of the universe is zero? I hope this isn't a gross misrepresentation of GR. Basically, such observers everywhere don't share a frame of reference with each other, because space is expanding between them, but they're also not moving through space relative to each other, so they can each be "at rest relative to the local zero-momentum frame of the universe"... I think.

Edited August 4, 2022 by md65536

[swansont]

10 hours ago, geordief said:

Is that just a mathematical convention?Could it just as well be the other way round ? (positive energy could be considered negative and vice versa)

 

Or does it have to be that way?

Positive and negative come out of the math so you'd have to make changes in the equations, and some of them really wouldn't work anymore.  The choice of what is zero is arbitrary but since what you are interested in is the change in energy between two states, it's often moot. if you chose a nonzero number you'd have it in two places that are subtracted, so it would cancel. Adding more terms that don't matter is kinda pointless. 

[Glancer]

On 8/1/2022 at 8:23 PM, MigL said:

Whether a property can be positive or negative, or simply an 'accounting' trick, or whether it even makes sense to consider energy on a global scale, is for people with better minds than mine to consider.

It could be an accounting trick.  In the same way that KE_i + PE_i = KE_f + PE_f. 

The kinetic energy of the big bang is KE = EBB (energy of the big bang).  Potential energy of curvature of spacetime equals zero. 

I assume you know where I"m going with this.  If I have to explain, it means you've never studied Conservation of Mechanical energy.

[MigL]

2 hours ago, Glancer said:

it means you've never studied Conservation of Mechanical energy.

I don't think anyone has, as there is no such thing.
Quit wasting forum bandwith with idiocy.

[Glancer]

5 minutes ago, MigL said:

I don't think anyone has, as there is no such thing.
Quit wasting forum bandwith with idiocy.

Why the hurt feelings?  I was only trying to talk about physics.

[MigL]

1 minute ago, Glancer said:

I was only trying to talk about physics.

You should learn some first ...

[Glancer]

24 minutes ago, MigL said:

You should learn some first ...

You didn't know that Conservation of Mechanical energy is physics?

Edited August 7, 2022 by Glancer

[Glancer]

What happened to all the people here who knew physics?  It's like dead around here.

[Markus Hanke]

6 hours ago, Glancer said:

You didn't know that Conservation of Mechanical energy is physics?

Spacetime isn’t a mechanical medium, so this is irrelevant. 

Also, it might surprise you to hear that the law of conservation of energy exists only in flat spacetime - in the presence of gravity, things become rather more complicated.

[Glancer]

12 minutes ago, Markus Hanke said:

Spacetime isn’t a mechanical medium, so this is irrelevant. 

Also, it might surprise you to hear that the law of conservation of energy exists only in flat spacetime - in the presence of gravity, things become rather more complicated.

Show me the experiment that supports your incredibly dubious claim.

And don't tell me any superstring theory bologna, because all that baloney is made up.

[exchemist]

7 hours ago, Glancer said:

You didn't know that Conservation of Mechanical energy is physics?

Mechanical energy can be converted into non-mechanical forms of energy, e.g. chemical or electrical energy. So it is obvious that mechanical energy is not conserved. 

[Glancer]

10 minutes ago, exchemist said:

Mechanical energy can be converted into non-mechanical forms of energy, e.g. chemical or electrical energy. So it is obvious that mechanical energy is not conserved. 

Conservation of energy refers to any kind of energy, not just mechanical.  Your knowledge of physics is corrupted.

If you put a mathematical theory based on elements with no experimental reality (strings, LQG, MWI) then you should get a CAT scan.  Or even better, you should go find some source of Common Sense, maybe a book about common sense, and read it.

[MigL]

Then why would you write something so wrong as 'conservation of mechanical energy' ???

Energy ( of all forms, even mass ) is conserved locally; not globally.