[shomp]

Mainstream physics has been delighted to ignore/abandon essential conservation laws when talking about the expanding universe. It's kinda weird, I tried publishing a paper on it recently and it was not received well. In general, if conservation laws are to hold, expansion must be balanced with [eventual] contraction, is that not obvious? Apparently it was quite contentious to say until... this article?

[antognini]

Noether's theorem tells us when we would expect conservation laws to hold and when we would expect them to fail. In the case of global energy conservation, there would have to be a global time invariance associated with the spacetime. But this is manifestly not the case in an expanding universe. It is generally not even possible to have a well defined notion of global energy in a dynamic spacetime.

[shomp]

Noether's theorem tells us when symmetry guarantees conservation, but it says nothing about conservation in the absence of that symmetry - it's not a biconditional statement. Talking about endless expansion is like observing 1 second of a pendulum's swing and concluding there's no time symmetry because it's only moving in one direction. The symmetry exists at the full cycle scale, not the snapshot scale.

[antognini]

It's true that it leaves open the possibility of a conserved quantity that is not associated with a symmetry. But the kinds of conservation laws we are thinking about, like conservation of energy, do originate from a symmetry. So if the symmetry is broken it is very reasonable to assume that the conservation law would be broken as well.

[ASalazarMX]

> In general, if conservation laws are to hold, expansion must be balanced with [eventual] contraction, is that not obvious?

Why would this be? The only physics we know is the one inside our observable universe, there could be variations beyond, or even unknowable laws that don't require conservation of matter outside the edge of the universe.

Our incredibly vast universe could be a minuscule blob feeding from an incredibly vaster parent universe, in which case it could be breaking conservation infinitely from our perspective.

[shomp]

Because energy cannot be created nor destroyed

[xwolfi]

Evidently energy was created, or it would not exist, would it ? It probably can be destroyed back to the pre-energy state in some way, just not on a scale we comprehend or even care about.

I suppose we're like bubbles on a boiling pot of water when the fire stops: all this agitation spreads out on the entire volume, and sure no energy was lost, but there are so little bubbles and so much water, once the heat has spread out entirely, the whole volume of water looks pretty dead.

[shomp]

>Evidently energy was created, or it would not exist, would it ?

It is constantly transforming, but that does not signify that it was created, that is beyond the evidence

[zygentoma]

No, the assumption was that dark energy is a property of space itself so it does not conserve energy at all in an expanding space.

Also this discovery does still is being explained with dark energy (albeit time varying …) so it still does not assume global energy conservation.

[mr_mitm]

Maybe this helps: https://www.preposterousuniverse.com/blog/2010/02/22/energy-...

My favorite quote:

> I like to think that, if I were not a professional cosmologist, I would still find it hard to believe that hundreds of cosmologists around the world have latched on to an idea that violates a bedrock principle of physics, simply because they “forgot” it. If the idea of dark energy were in conflict with some other much more fundamental principle, I suspect the theory would be a lot less popular.

[shomp]

You go into a cafe and order a slice of cake. One is delivered. You order three more, three more are delivered. You conclude that the kitchen has infinite cakes based on the observable evidence. That's the argument.

[frotaur]

I mean no disrespect, but are you a trained physicist, or at least familiar with the 'mainstream material'?

Because there is no shortage of 'crackpots' that have 'obvious' solutions to unsolved physics problems, and that want to publish papers about it.