Linked Questions

65
votes
6answers
17k views

Is the total energy of the universe zero?

In popular science books and articles, I keep running into the claim that the total energy of the Universe is zero, "because the positive energy of matter is cancelled out by the negative energy of ...
31
votes
5answers
4k views

Redshifting of Light and the expansion of the universe

So I have learned in class that light can get red-shifted as it travels through space. As I understand it, space itself expands and stretches out the wavelength of the light. This results in the light ...
17
votes
3answers
13k views

Is the law of conservation of energy still valid?

Is the law of conservation of energy still valid or have there been experiments showing that energy could be created or lost?
26
votes
3answers
9k views

Energy conservation in General Relativity

I understand that energy conservation is not a rule in general relativity, but I'd like to know under what circumstances it can still be possible. In other words, when is it possible to associate a ...
18
votes
5answers
7k views

Conservation law of energy and Big Bang?

Did the law of conservation of energy apply to the earliest moments of the Big Bang? If so, what theoretical physics supports this? I hear that Einstein's theory of relativity disputes the law of ...
8
votes
2answers
724 views

Pass to globally conserved currents from locally conserved currents in curved spacetime

Let us begin with a Lagrangian of the form $$\mathscr L= \frac 12 \sqrt{-g}g^{\mu\nu}\partial_\mu\phi(x)\partial_\nu\phi(x)+\mathscr L_g,$$ where $$\mathscr L_g=\frac 1{16\pi k}\sqrt{-g}R.$$ ...
7
votes
3answers
548 views

Is energy conserved in general relativity? Does $\nabla_aT^{ab}_{\rm matter}=0$ represent the conservation of energy and momentum?

For example, the radiation dominated cosmology, the energy density of radiation is proportional to $a^{-4}$ and the volume is proportional to $a^3$, where $a$ is the scale factor. So the total energy ...
3
votes
2answers
644 views

What is the total energy of the Universe? [duplicate]

The Law of Conservation of Energy states that: Energy can't be created nor can be destroyed. It only changes from one form to another. According to this the total energy in a closed system never ...
1
vote
2answers
371 views

Perpetual Motion Machines [closed]

If you go on YouTube, you will find a large number of machines that work for almost forever. But why do all of them stop working after some time? Which Law (Other than Conservation of Energy) ...
3
votes
0answers
151 views

Avoiding Pseudo-tensors when addressing global conservation of energy in GR

Discussions about global conservation of energy in GR often invoke the use of the stress-energy-momentum pseudo-tensor to offer up a sort of generalization of the concept of energy defined in a way ...