8 replies to this topic

[Kwantumnaut]

Hello. First let me say I don't know much about thermodynamics, so bare with me lol But I'm just curious as to how the law of conservation of energy (energy cannot be created or destroyed) is considered to be, and how we are certain it is, and always will be unchanging, irrefutable 100% fact.

 

I wonder this mainly because a lot of other theories, information and facts are based and rely on this law, but there have been other laws, facts etc. throughout the world/history of science, that were once said to be proven unchanging and irrefutable, but at some point ended up being disproved or modified, so how do we know the same can't/won't be the case for the law of conservation of energy? 

[lee14]

Inadequately composed 'laws' tend to be overturned when measurements and data acquisition improvements reveal flaws. Then a theory is modified, updated, or replaced. The conservation of mass/energy is founded on physical theory that has never shown the slightest observational defect, and is error free in matching the accuracy of measurement to the underlying explanation. That said, physics is not a complete explanation for every phenomenon, dark matter, dark energy, and black hole interiors remain undefined, partly because Relativity and Quantum Mechanics disagree at certain scales. As better measurements or data are found, both theories will be encompassed in a more complete one. We rely on both, and Conservation of mass/energy, because they work, and the predictions they make within their defined parameters, is flawless.

 

Lee

Edited by lee14, 30 November 2020 - 08:52 AM.

[ButterFly]

The scienctific method can never prove a theory.  All it can do is reject a null hypothesis.  Within a realm, when enough experiments are conducted, and no contrary evidence is presented, a "law" is declared.  Just because there is general relativity does not mean that Newton's Laws don't work within their realm.  Go beyond that realm, and Newton's Laws don't hold.

 

Energy is not completely understood and agreed upon in general relativity.  Neither is the conservation of energy at cosmological timescales.  One day, long ago, all this energy just appeared out of nowhere?  Well, it's here!

 

At short enough time scales, the idea of conservation of energy comes from the "laws of physics" being invariant in time.  The time symmetry leads to conservation of energy in the same way that position symmetry leads to conservation of momentum and rotational symmetry leads to conservation of angular momentum.  See Noether's Theorem.  At root is the idea that we know what the laws are to say what their symmetries are.  Go outside of the realm where those laws apply and it's anyone's guess.

[bitnick]

Isn't redshift due to the expansion of space one example of where energy is not conserved?

[DaveC2042]

Isn't redshift due to the expansion of space one example of where energy is not conserved?

This is better characterised as an open question than a failure of energy conservation.

 

A couple of points:

• At the risk of anthropomorphism,  the universe seems to go to a good deal of trouble to conserve energy (more properly mass-energy) generally.  Things like potential energy, nuclear binding energy, gravitational redshift etc all form a pretty complicated package doing this with great care and subtlety.  That is why physicists see it as a bedrock law and will generally see an apparent violation as most likely a lack of understanding on our part;
• Remember energy isn't really a thing, the way mass or charge are.  It's just an abstract quantity we calculate because it turns out to be really useful, its conservation being a particularly useful aspect of it.  On occasion, we have expanded the definition of it in order that it might still be conserved.  Nuclear binding energy is a good example.  So when we look at metric expansion, one possible way of approaching it is to say there is some field, acting as reservoir of energy, driving the expansion, and thus conserving energy. Eg dark energy.  A similar thing has been done with entropy and black holes - the 'problem' of entropy decreasing when you chuck matter into a black hole was resolved by considering the event horizon surface area to be equivalent to the black hole's entropy.  Of course, this is all just handwaving until you have a specific proposal where the maths all stacks up.

[ButterFly]

 

• Remember energy isn't really a thing, the way mass or charge are.  It's just an abstract quantity we calculate because it turns out to be really useful, its conservation being a particularly useful aspect of it.

It is also good to remember that even in systems where energy is conserved, it's the change in energy that is the physical quantity.  One can add, say, "five" to all the values of energy and still get the same physics out.  That leads to question llike: What happens to the Dirac sea when one is moving?

[bcgilbert]

It is also good to remember that even in systems where energy is conserved, it's the change in energy that is the physical quantity.  One can add, say, "five" to all the values of energy and still get the same physics out.  That leads to question llike: What happens to the Dirac sea when one is moving?

You may find this link interesting?

 

https://en.wikipedia...anck's constant.

 

Barry

[bcgilbert]

A single bare hydrogen atom in an empty void is likely to allow the electron to approach the proton.  there are two possible models for this, firstly the electron acceleration  will radiate freely due to the orbital motion and without  the restoring effect of the other 10^80 hydrogen atoms in the universe (zero point radiation).     Secondly without any reference material in the void (Mach's principle), the electron can have no knowledge of acceleration due orbital motion,  and simply be attracted to the proton without centripetal force to balance the coulomb force.    Feynman did not know this and only considered the hydrogen atom in isolation, not realizing the natural equilibrium resulting from all the hydrogen atoms attempting to allow their electrons to radiate freely and  approach their  protons. this will give you the answer to the puzzle of the infinite energy of the zero point radiation. quite a lot but by no means infinite.  E =MC^2 indicates quit a bit of equivalent mass, hhmmm I wonder?

 

Just saying

Barry

[ButterFly]

You may find this link interesting?

 

https://en.wikipedia...anck's constant.

 

Barry

Oh; I do.  The calculated cosmological constant is a hundred orders of magnitude off from the measured value.  That's a problem.  There's no inertial reference frame one can pick in this scenario.

 

Even though recent measurements of the cosmological constant disagree (see the lecture link I posted earlier), the disagreement is not quite that bad.