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Question69
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- TL;DR Summary
- Is energy conserved in GR?
Is energy really not conserved in a constantly expanding universe?
Is energy really not conserved in a constantly expanding Universe?
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In summary, the conversation discusses the conservation of energy in a constantly expanding universe and references a blog post by Sean Carroll on the topic. It also mentions an Usenet Physics FAQ article that discusses the concept in further detail. The conversation concludes with the confirmation that there are no further questions on the topic.
- #2
PeterDonis
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The short answer is, it depends on what you mean by "energy" and what you mean by "conserved". 
Sean Carroll's blog post on the topic is a good place to start:
https://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/
Sean Carroll's blog post on the topic is a good place to start:https://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/
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PeterDonis
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Credit where credit is due, this bon mot is not original with me, it comes from this Usenet Physics FAQ article, also worth reading:PeterDonis said:it depends on what you mean by "energy" and what you mean by "conserved".
https://math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html
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Question69
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Oh I've read that already, it was when I first found about it really, I just thought I'd ask you guys because maybe Sean is wrong :)PeterDonis said:The short answer is, it depends on what you mean by "energy" and what you mean by "conserved".
https://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/
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PeterDonis
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Um, no.Question69 said:
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PeterDonis
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That would have been a good thing to mention in the OP of this thread.Question69 said:
Do you have any further questions on the topic?
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Question69
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I should have, yes, and no.PeterDonis said:
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PeterDonis
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I'll take that as "no further questions". Thread closed.Question69 said:
1. Is energy truly not conserved in a constantly expanding Universe?
According to the law of conservation of energy, energy cannot be created or destroyed, only transformed. However, in a constantly expanding Universe, the total amount of energy remains the same, but it becomes more spread out and less concentrated. This means that while energy is still conserved, it may not be as easily observable or usable in certain areas of the Universe.
2. How does the concept of dark energy affect the conservation of energy in an expanding Universe?
Dark energy is a theoretical form of energy that is thought to be responsible for the observed accelerated expansion of the Universe. It is believed to make up about 68% of the total energy in the Universe. While the exact nature of dark energy is still unknown, its presence does not violate the law of conservation of energy. It is simply a form of energy that we do not fully understand yet.
3. Can energy be created or destroyed in a constantly expanding Universe?
No, energy cannot be created or destroyed in any scenario, including a constantly expanding Universe. As mentioned before, the law of conservation of energy states that energy can only be transformed from one form to another. In an expanding Universe, the total amount of energy remains the same, but it may appear to be lost or gained due to the expansion and distribution of energy.
4. How does the expansion of the Universe affect the conservation of energy on a smaller scale?
The expansion of the Universe does not affect the conservation of energy on a smaller scale. The law of conservation of energy still applies to all systems, regardless of their size or location in the Universe. The only difference is that the energy may be more spread out and less observable on a smaller scale due to the overall expansion of the Universe.
5. Is the concept of energy conservation still relevant in an expanding Universe?
Yes, the concept of energy conservation is still relevant in an expanding Universe. While the total amount of energy in the Universe may remain constant, its distribution and concentration may change due to the expansion. This does not violate the law of conservation of energy, but it does require us to consider the effects of expansion when studying and observing energy in the Universe.
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