
Energy Is Not Conserved (2010) - monort
http://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/
======
batbomb
Martin Perl, the author mentioned in the paper, was a Nobel prize winner and
one of the first people I met when I got to SLAC. His office was across the
hall from mine. Unfortunately, Martin passed away this year. He was a very
nice, smart, and humble man.

------
carapace
This cleared up that question for me. Noether showed that every physical
symmetry implies a conservation law and vice versa, the symmetry of time flow
and the conservation of energy are one such pair. Due to the fact that time is
not flowing uniformly (Relativity) energy is not conserved.

~~~
antognini
The converse of Noether's theorem does not turn out to be true in general.
Noether showed that if there is a symmetry in the system then there is a
corresponding conservation law. But the existence of a conserved quantity does
not (in general) imply the existence of some symmetry in the physical system.

(I should note that there are more careful ways to get something that looks
like the converse of Noether's theorem, but the literature is fairly
complicated -- you have to distinguish between trivial conservation laws and
non-trivial conservation laws. Here's one answer online:
[http://physics.stackexchange.com/questions/24596/is-the-
conv...](http://physics.stackexchange.com/questions/24596/is-the-converse-of-
noethers-first-theorem-true-every-conservation-law-has-a-sy))

~~~
eru
Yes. Though carapace's argument works on a weaker level: the symmetry is
broken, so we have no particular reason to expect a conservation.

------
clavalle
When the Universe is taken as a whole do the changes of gravitational energy
in spacetime exactly cancel out the changes of matter energy (including dark
matter) due to the expansion of spacetime? How do we know (is there some
mathematical reason to believe this is the case)?

When the author says that spacetime absorbs matter energy or gives matter
energy, what does that really mean? Does it mean it can be used as a
convenient sink or well in regards to changes of potential energy? What are
the rules governing that transfer or do we just make things balance and decide
that spacetime did it?

I am trying to shake this uncomfortable feeling that it is too convenient. I'd
love to know the ground those kinds of operations stand on.

------
lotsofmangos
If energy is not conserved across distortions in space time, then neither is
momentum. That em-drive people have been testing is forcing a distortion in a
resonating wave that should just be varying the flux density from one end to
the other, it it looks the epitome of something that should just sit there and
do nothing. It's a lopsided microwave oven. But that could make a pinch in
spacetime that isn't completely symmetrical at the neck, so you end up with a
sort of spacetime ramjet.

Probably not, but it would be nice.

edit - this nonsensical waffle was brought to you today by too much coffee,
not enough sleep, and the number 7.

~~~
PeterWhittaker
Well, we know that momentum - and energy - are only conserved across a long
enough timeframe. I'm working from 30 year memories year (special relativity
class during my undergrad) so bear with me....

Consider a charged object moving at high speed (nearing c) toward an object
with the same charge, but on a path to pass "beside it" (it doesn't really
matter by how much, so long as the one will not hit the other); treat the
second object as a stationary reference frame, to make this conceptually
easier.

At any given time, there is force of repulsion between the two objects.
Normally (relative speed much, much less than c), this force can be
approximated as an r-squared force acting along the line separating the two
objects.

So far so good. No problems with conservation of anything here, all the
vectors in the various force diagrams add up just fine.

But the objects are moving relative to each other at speed nearing the speed
of light, and the repulsive force is transmitted at the speed of light...

...which means that at any given instant, the force exerted on one particle by
the other is parallel not to the line drawn from one to the other at the
moment the force is exerted (at the moment it arrives) but parallel to that
line from a few moments ago.

At any given time, when the objects are close enough to one another, the
forces acting on each object are an angle to the line drawn from one the
other.

In order to have conservation of anything, one has to make a vector
integration over a sufficiently long time frame ("long enough" before and
"long enough" after the collision, that is, the moment the incoming object
passes by or begins moving away from the other).

Otherwise, things just don't add up.

Like I said, I am casting my mind back to a brain-popping moment from 30 years
ago in which we sat there slack jawed, eyes agape, and a little aghast,
starting at the blackboard while the prof stood there with a Cheshire Cat grin
tossing his chalk up and down, waiting for us to accept - or at least merely
acknowledge - that we weren't in Kansas anymore, that the universe was rabbit
holes all the way down, and that we'd been lied to since junior high.

Fun times.

~~~
DougMerritt
> momentum - and energy - are only conserved across a long enough timeframe

> In order to have conservation of anything, one has to make a vector
> integration over a sufficiently long time frame

My understanding was that the time frame was strictly a matter of the
Heisenberg Uncertainty Principle -- if the time is less than specified by HUP
for the situation, then conservation generally does not hold, but if time is
greater than that, then conservation is strictly held.

The simple model of virtual particles involved in Feynman diagrams is that
they are precisely the ones that take time less than HUP.

Unless you're talking about relativistic effects where adjustments are needed,
but after those adjustments, it's back to the above again.

~~~
PeterWhittaker
Well, awesome that to be the case, that conservation does not hold at time
less than Thup.

That leaves an awful lot of interesting physics happening to cause
conservation to emerge at macroscopic scale.

HC SVNT DRACONES, no?

~~~
DougMerritt
To some extent, but mostly this is long-explored territory with few dragons.

It's not often put this way, but you _could_ say that the virtual particles <
HUP establish the wavefunctions that have effects fully evaluated by the time
of > HUP, such as the phase cancellations that cause light to take the path of
least time, which is otherwise puzzling.

------
ggchappell
This is interesting, and I would like to find out more about it. That equation
with the Del & T is meaningless to me, since I don't know what the letters
stand for. A search for "energy-momentum conservation" turns up lots of
college physics labs about energy conservation and momentum conservation.

Can anyone help me find out more?

Also, I have read that Newton's three laws of motion, if suitably formulated
so that they are meaningful in a non-euclidean space, and being careful to say
"derivative of momentum", NOT "mass times derivative of velocity", continue to
be exactly right, as far as modern physics is aware. But since Newton's laws
essentially say, "momentum is conserved", that would not be true if this
article is correct (right)?

