Monday, July 18, 2011

Poll 83 - Is Energy Not Conserved?

Poll 83 - "Cosmologist Dr. Sean Carroll says energy is not conserved in general relativity, because as our spacetime universe expands so does the amount of energy. Do you agree with him?"

This poll ended July 13 2011. As you can see here, more people disagreed than agreed, which is really not that surprising: haven't we all been taught that there is a finite amount of energy in the universe? Isn't the Law of Conservation of Energy one that can never be broken? Every time a new "free energy" device is announced, the critics chuckle and say "that's impossible, you can't get something for nothing". So what's Dr. Carroll thinking about here?

I've talked in this blog a number of times about Sean Carroll's writing, and it should be obvious by now that I'm a fan. His blog on the Discover Magazine website is called "Cosmic Variance", and if you go there right now I'm sure you'll find some new entries with some nourishing food for thought. This poll question relates to an entry of his from 2010 called Energy is Not Conserved, and I invite you to follow the link and read the entire piece. Here's a couple of paragraphs to whet your appetite: 
...It’s clear that cosmologists have not done a very good job of spreading the word about something that’s been well-understood since at least the 1920's: energy is not conserved in general relativity.

The point is pretty simple: back when you thought energy was conserved, there was a reason why you thought that, namely time-translation invariance. A fancy way of saying “the background on which particles and forces evolve, as well as the dynamical rules governing their motions, are fixed, not changing with time.” But in general relativity that’s simply no longer true. Einstein tells us that space and time are dynamical, and in particular that they can evolve with time. When the space through which particles move is changing, the total energy of those particles is not conserved.
There's much more to his entry than that, but reading these words is what prompted me to create the poll question we're looking at today. If you are in the camp who disagrees, please read Dr. Carroll's whole entry and see if he changes your mind about this fundamental question on the nature of our reality.

Some of the other entries where I've talked about Sean Carroll's ideas include I'm You from the Future, Flow, How to Time Travel, Temporal Mass, and What's Around the Corner? You might also recognize him from his appearances on the excellent documentary series Through the Wormhole with Morgan Freeman, which if you haven't had a chance to watch I would highly recommend. Next week, we're going to talk about some of the ideas raised in that series with a set of entries that begins with "Imagining the Second Dimension".

Till then, enjoy the journey!

Rob Bryanton

Next: New video - Poll 77 Living in a Simulation

1 comment:

Myrtone said...

Is it common sense that energy is not conserved? There may be a corresponding conservation law to every definable symmetry, but in order for symmetry to be guarateed, there has to be intrisic certainty, determinism and no mixed states. With non-determinism and mixed states, how can we prove that any symmetry is not a quantum coincidence? Also, vehicles, aircraft and vessels nood energy to keep moving.

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