Not that I believe this would work, but I have a perpetual motion machine idea.
I’m told you can convert between energy and mass. So first step, take a bunch of mass on Earth’s surface, turn it into energy.
Shine it as light up to a space station in Earth orbit.
Collect the light, turn it back into mass, drop it. Collect kinetic energy, repeat.
Why wouldn’t this work? Is there a slightly different energy-to-mass ratio depending on where you do the conversion? (Edit: I just realized this would give a way to tell the difference between “You’re in an elevator accelerating upward” and “You’re in an elevator standing ‘still’ on Earth” from the inside, which if I remember correctly you’re not supposed to be able to do) Would the light lose energy as it traveled upward (Does differently-shaped space redshift it)? Is the answer the same if instead of gravity you used another force? (Say Earth was positively charged, and you converted negatively charged mass to energy, and back)
Would the light lose energy as it traveled upward (Does differently-shaped space redshift it)
Yes. You do lose energy moving light uphill, even if you have perfect emitters and collectors.
Is the answer the same if instead of gravity you used another force? (Say Earth was positively charged, and you converted negatively charged mass to energy, and back)
Say Earth was positively charged, and you converted negatively charged mass to energy, and back
Electric charge is conserved, so you can’t convert only negatively charged matter to energy. You’d need some positively charged matter as well (ideally the corresponding antimatter).
While true, that can’t be all that’s wrong with it, because otherwise if you did this even once, turning all your mass to waste heat, you’d still have violated the First Law. It would still be more useless energy than you started with. Right?
Even the highest entropy energy can still be used to do work, it’s just not as efficient. I would predict that a team of engineers/physicists could exploit this to get free energy in the counter-factual universe where this is the only difference between our laws of physics.
I would expect most of the loss to take place in the collection stage, but short of antimatter, a perfect energy-mass conversion technique doesn’t seem to be available, so there are probably plenty of waste particles when it’s converted to energy as well.
(The parent was at −4 when I found it. When I expanded the comment to read it, I was extremely confused, because it did not fall into my “LW users will downvote this heavily” pattern. ??? )
I didn’t downvote it because it was a plausible-sounding suggestion which led to a clarifying discussion, but my guess is that some downvoted it for giving a somewhat irrelevant/misleading answer. As Adele_L explains, heat loss pertains to the Second Law, while the proposed setup has the more fundamental problem of violating the First Law and even assuming away heat loss does not work because of gravitational redshift, as Plasmon explains.
Not that I believe this would work, but I have a perpetual motion machine idea.
I’m told you can convert between energy and mass. So first step, take a bunch of mass on Earth’s surface, turn it into energy. Shine it as light up to a space station in Earth orbit. Collect the light, turn it back into mass, drop it. Collect kinetic energy, repeat.
Why wouldn’t this work? Is there a slightly different energy-to-mass ratio depending on where you do the conversion? (Edit: I just realized this would give a way to tell the difference between “You’re in an elevator accelerating upward” and “You’re in an elevator standing ‘still’ on Earth” from the inside, which if I remember correctly you’re not supposed to be able to do) Would the light lose energy as it traveled upward (Does differently-shaped space redshift it)? Is the answer the same if instead of gravity you used another force? (Say Earth was positively charged, and you converted negatively charged mass to energy, and back)
Yes. You do lose energy moving light uphill, even if you have perfect emitters and collectors.
I don’t think you can do that. Photons have no electric charge.
Electric charge is conserved, so you can’t convert only negatively charged matter to energy. You’d need some positively charged matter as well (ideally the corresponding antimatter).
My guess is that you’d lose some of the energy as heat every time you tried to convert it into mass.
While true, that can’t be all that’s wrong with it, because otherwise if you did this even once, turning all your mass to waste heat, you’d still have violated the First Law. It would still be more useless energy than you started with. Right?
Energy tends to become more useless, so I don’t see how that’s an argument against my point.
This is true, and is an informal version of the second law of thermodynamics.
But this violates a different law, conservation of energy.
Even the highest entropy energy can still be used to do work, it’s just not as efficient. I would predict that a team of engineers/physicists could exploit this to get free energy in the counter-factual universe where this is the only difference between our laws of physics.
I would expect most of the loss to take place in the collection stage, but short of antimatter, a perfect energy-mass conversion technique doesn’t seem to be available, so there are probably plenty of waste particles when it’s converted to energy as well.
(The parent was at −4 when I found it. When I expanded the comment to read it, I was extremely confused, because it did not fall into my “LW users will downvote this heavily” pattern. ??? )
I didn’t downvote it because it was a plausible-sounding suggestion which led to a clarifying discussion, but my guess is that some downvoted it for giving a somewhat irrelevant/misleading answer. As Adele_L explains, heat loss pertains to the Second Law, while the proposed setup has the more fundamental problem of violating the First Law and even assuming away heat loss does not work because of gravitational redshift, as Plasmon explains.