[BreakfastB0b]

Conservation of energy is not fundamental. Noether’s Theorem shows that Conservation Of Energy only arises in systems that exhibit “Time Translation Symmetry” i.e. conducting an experiment now, and conducting an experiment later always are the same.

If you fling a charged particle like an electron through an increasing magnetic field, it will appear to gain energy.

Locally our universe seems to obey Time Translation Symmetry and thus also Conservation of Energy. However the expanding universe is not Time Translation Symmetric, at the scale of galactic clusters new “energy” is created all the time just like the electron in the magnetic field. That’s what “dark energy” is.

All the different conservation laws have roots in symmetries of the system.

[hinkley]

> If you fling a charged particle like an electron through an increasing magnetic field, it will appear to gain energy.

“If I place a particle into an energetic system, it gains energy.” This is an even worse example than the one in the article. You’re trying to define a closed system that is stealing energy from outside the “closed system”. That’s the same logical fallacy that leads people to think they have discovered a Perpetual Motion Machine. How do people get into advanced topics like Time Translation Symmetry without understanding (and being able to explain) the basics?

[BreakfastB0b]

I have a Physics degree for what it's worth. Though I'll admit I didn't articulate what I meant clearly.

The electron example was assuming that the increasing magnetic field was part of this hypothetical toy universe that violates time translation symmetry. Obviously constructing such experiment in our universe it's not surprising that the electron gains energy because as you said, it's not an isolated system. When considering the system generating the magnetic field it becomes obvious that the overall system does not gain energy.

However our actual universe, at the galactic scale, is just like the toy example. New Space / Energy is created out of nothing as the universe's expansion accelerates. There is no paradox here because conservation of energy is not fundamental but emergent from symmetries via Noether's theorem. Space is a "material" that is not "diluted" by expansion and contains energy.

The inflaton field at the heart of hyperinflation / big bang theory also expands without dilution.

Perhaps there is some larger system our universe is embedded in that does respect time translation system / conservation of energy and the expansion is being driven by a larger process loosing energy but we can't observe it.

[leephillips]

And on the scale of the universe as a whole, energy continually decreases. Expansion entails increase of the wavelength of all light, which implies decrease in energy.

[kgwgk]

I don’t think the answer is so clear for the universe as a whole. The energy of the photons decreases due to the expansion - but the expansion can have other additional effects.

[eli_gottlieb]

Energy doesn't decrease. Entropy increases.