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When you send a rocket into space, you burn chemicals (releasing energy located in electrons in the chemical bonds holding the atoms together) gaining thermal e

When you send a rocket into space, you burn chemicals (releasing energy located in electrons in the chemical bonds holding the atoms together) gaining thermal energy (the energy of moving atoms in hot rocket exhaust) which is then redirected into kinetic energy (still moving atoms, but they're all moving in the same direction, and more orderly about it). When the spaceship moves upwards relative to a large mass (Earth), this kinetic energy is traded for gravitational potential energy. It's still associated with the atoms and other particles, just like the kinetic energy was. This does mean that objects in distant space have more of this energy than objects at the bottom of a gravity well, and are therefore more massive (because of mass-energy equivalence). Falling into an intense gravity well is actually one of the more efficient ways to convert mass into energy, which is why the area around black holes is often particularly energetic, with the matter falling in emitting energetic X-rays. This is why you can see quasars even though they are billions of light-years away (the radiation heats the surrounding material and it is very bright.) Besides general physics reading, I can recommend the book "Einstein's Universe" to help build a general understanding of both special and general relativity, with particular regard to matters such as mass-energy equivalence.

saagarjha 6y ago
> Falling into an intense gravity well is actually one of the more efficient ways to convert mass into energy, which is why the area around black holes is often particularly energetic, with the matter falling in emitting energetic X-rays. The heat comes from gravitational compression and friction with other material in the accretion disk, not because objects at the bottom of a gravity well have less mass.
- fennecfoxen 6y ago
  It's true that object in freefall being attracted towards a gravity well does not have less mass as it approaches deeper parts in the well. However, it will have less rest mass from its potential energy, and more mass due to its kinetic energy. If the object continues on a trajectory past the gravity well and out to space beyond, it will lose that kinetic energy, and regain the potential energy. So in that sense, it's true: the overall mass doesn't change. But if the object smacks into something, like an accretion disk around the black hole, or the atmosphere of a planet, then the kinetic energy escapes the object, and is lost to the surrounding system (through mechanisms like friction and compression, as you've mentioned). Per Einstein, this lost energy really does mean the object has lost mass.

saagarjha 6y ago

> Falling into an intense gravity well is actually one of the more efficient ways to convert mass into energy, which is why the area around black holes is often particularly energetic, with the matter falling in emitting energetic X-rays. The heat comes from gravitational compression and friction with other material in the accretion disk, not because objects at the bottom of a gravity well have less mass.

fennecfoxen 6y ago
It's true that object in freefall being attracted towards a gravity well does not have less mass as it approaches deeper parts in the well. However, it will have less rest mass from its potential energy, and more mass due to its kinetic energy. If the object continues on a trajectory past the gravity well and out to space beyond, it will lose that kinetic energy, and regain the potential energy. So in that sense, it's true: the overall mass doesn't change. But if the object smacks into something, like an accretion disk around the black hole, or the atmosphere of a planet, then the kinetic energy escapes the object, and is lost to the surrounding system (through mechanisms like friction and compression, as you've mentioned). Per Einstein, this lost energy really does mean the object has lost mass.