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I know the conservation of energy doesn't allow that, and i saw a question on this forum about infinite energy: Why can't I do this to get infinite energy?, it says we can convert matter into energy and pump it up and convert back to matter and let it fall to generate energy. Comments were of full this is impossible because of this and this etc.

The reason was General Relativity was telling that gravity affects energy as well, photons would slow down. But if it does, doesn't this mean energy is permanently lost and not converted to anything else? Energy is conserved because sum of kinetic energy and potential energy is always same, as long as particle doesn't give its energy to another thing such as colliding with it.

Then light mustn't lose his energy, never unless he collides with another thing. Comments were saying gravity will slow it down and light will lose speed and kinetic energy, but where did the kinetic energy go? It can't be potential energy, because potential energy requires mass and distance, where photon has no mass and no potential energy. So kinetic energy must always be same. Also, how gravitation affects a thing that even has no mass? Mass is energy yes but is energy necessarily mass? Why should all things that affect mass also affect energy, if not why photons slow down.

Some comments said there is no way to matter to energy and energy to matter but antimatter + matter is gamma rays and gamma rays when condensed could be converted to antimatter and matter. Matter can't do this conversion on its own, but it doesn't matter that it couldn't.

Some comments said energy will be used to make light go upwards will be equal to harvested energy from matter potential energy but why would energy be used to make light go upwards?

Qmechanic
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Yıldırım Gaming TR
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2 Answers2

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To put a simple answer, light travels along spacetime, gravity curves spacetime, hence gravity affects light.

Travelling across this curved spacetime, the photons are red-shifted i.e. increased wavelength. As we know, $$ c=\nu \times \lambda \tag{1} $$ and $$ E=h\nu \tag{2} $$ Light doesn't slow down. But the path it now takes across spacetime might be longer (as its curved) than it would be if spacetime was flat. As it has an increased $\lambda$, $\nu$ is smaller so the photon's energy is now less.

SamuraiMelon
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  • Sorry if it's a bad question but is the amount of antimatter i can create with this energy lowered particle is less than i started with? – Yıldırım Gaming TR Apr 23 '20 at 20:57
  • The total energy of the antimatter at creation will be the same as the energy of the photons used to make the antimatter at the time the antimatter is made. Energy is always conserved. – SamuraiMelon Apr 23 '20 at 21:23
  • But you also said gravity affect light's energy, so if i gained 100GJ from a annihilation and pump photons up with a perfect reflactor or optic cable 10km, will i able to create the same amount of matter and antimatter at the 10km away from the surface? – Yıldırım Gaming TR Apr 24 '20 at 12:34
  • @YıldırımGamingTR Yes, you've specifically specified that you're 'pumping' the photons up. That pumping to get the photons from the surface to 10km away, would require energy. – SamuraiMelon Apr 25 '20 at 15:08
  • But what would happen if used no energy for that, if i made a long pipe of perfect reflactors and transport photons just by reflecting to top? – Yıldırım Gaming TR Apr 26 '20 at 08:47
  • @YıldırımGamingTR Then the photons would lose energy escaping the potential well up to your 10km. Its the exact same principle as how you need to use energy to jump from the Earth's surface. At this point, you could just think of basic Newtonian principles in terms gravity exerts a force on the photon, so the photon loses energy trying to move in the opposite direction. – SamuraiMelon Apr 26 '20 at 13:41
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General Relativity was telling that gravity affects energy as well, photons would slow down.

From the viewpoint of a distant observer, light slows down as the gravitational potential increases (e.g. near black holes) AND speeds up as the gravitational potential decreases (in areas of space without masses near and around them).

But if it does, doesn't this mean energy is permanently lost and not converted to anything else?

It does not, see the explanations above. In addition, it is important to understand that the change in velocity perceived by a distant observer is not acceleration from the point of view of the photon. The movement on the geodetic path (seen as a curve from the distant observer) always happens without any acceleration. Your geodetic path will be different and more curved, but you will never feel any acceleration.

Then light mustn't lose his energy, never unless he collides with another thing.

Exact.

HolgerFiedler
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