Energy Is Not Conserved in an Expanding Universe
I know, I know, I can hear you all harumphing and spluttering all the way over here.
HarumphHarumph What you do mean, man!? Have you gone mad? Harumph, I say to you!
The fact is, there’s nothing in Newton’s physics that requires that energy be conserved. The idea that energy is neither created nor destroyed comes out of the idea that the stage physics plays itself out on is invariant and unchanging with time.
And anyone who knows anything about general relativity knows that space and time are NOT invariant.
Spacetime is very, ummm, variant.
Let’s forget about dark energy and dark matter for the moment, and let’s just consider the stuff in the universe that we CAN see and interact with.
All of the energy in the universe is of two types:
- The rest energy of all mass particles: protons, neutrons, electrons. This is the energy in all matter given by E=mc^2. These particles are slow moving compared to the speed of light.
- The energy of radiation particles: photons, neutrinos, etc. These particles are moving close to the speed of light.
In an expanding universe, the universe now is bigger now and was smaller some time in the past. The mass particles, of which there is a constant amount, does not change and is not affected by the expansion other than to become more dilute (i.e., there are fewer of them in a given volume of space).
The radiation particles on the other hand, are redshifted as the universe gets bigger. They actually lose energy.
How do we know this? By looking at the cosmic microwave background radiation. These are the photons that were present at the point the universe became transparent (don’t worry about what that means right now). Those photons have since redshifted into the microwave region of the spectrum.
These photons were at a much higher energy when they zoomed free than they are now. They’ve lost a lot of energy over the course of 14 billion years, now they are a cold 3 degrees Kelvin radiation background.
So, long story short, all of the radiation particles are losing energy due to the expansion of spacetime. And we’re never gonna get that energy back.
As for dark energy, well, we’re constantly getting MORE of that. For all we know about the stuff so far, it’s literally coming out of nowhere.
Please, continue your regularly scheduled harumphing…
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4 opinions for Energy Is Not Conserved in an Expanding Universe
Diddy Mac
Dec 1, 2007 at 1:15 pm
So as the universe expands the the photons lose energy. Is it not he case that there are more photons present now to counter them losing energy so the sum total energy is retained? How about the photons don’t lose any energy cause the red shift means a less intense amount of qaunta and that’s indepenent of a photons energy level. Yeah it’s cold out there, but if it’s possible for a radiation particle to lose energy it must pass onto another particle.
lee
Dec 4, 2007 at 5:51 am
diddy mac is exactly right
……..wen the particle loss enegry ..its doesnot mean tat the enrgy disappears ..i may be taken by another particle….
and if we take the whole system of universe into cosidration…offcourse the energy is conserved………plzz mail me to munnabhai_1433@hotmail.com,if you r ready to talk with me regarding this matter/////…..
r06u3AP
Dec 9, 2007 at 9:07 pm
I disagree with Diddy Mac. THe photons do indeed lose energy from the expansion. And, no, there aren’t more of them and no, they didn’t transfer any energy to other particles. They are red-shifted.
There is an idea that if energy is conserved cosmically, then the net energy of the Universe is exactly zero. How can this be? Well, for regular (”positive”) energy in the form of mass, material interactions and radiation to exist, there must be a “negative” energy that cancels it all out.
I would suggest that the negative energy attribute of the Universe is spacetime itself, along with it’s dynamic properties of expansion and acceleration due to dark energy. And if you’re looking for a quantum principle that fits in with that, what could be more fitting than the idea that matter and spacetime are quantum conjugates that arose at the moment of the Big Bang, driven by the “negative/dark” energy hyperinflation of spacetime that overrode gravity as mass/matter/radiation came into existence simultaneously?
It all seems pretty simple to me!
Expanding Universe and Conservation of Energy
Dec 10, 2007 at 5:04 pm
[…] been getting lots of questions about my post on how conservation of energy isn’t conserved in an expanding universe. Happily, I just ran across this excellent post from Sean that may clarify things a bit more. Does […]
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