Gregory's Server@drewdevault You can’t directly compare energy in different inertial frames without a transformation function. This is even true in non-relativistic mechanics: If you’re standing still and I’m running towards you, I have nonzero kinetic energy from your point of view. If we’re running next to each other at the same velocity, I have zero kinetic energy in your frame of reference.
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 @pmdj sure, but just assume I pack fuel for accelerating up to cruise speed and back down again, this is X stored energy. Then at cruise speed I funnel the CMB into some batteries, storing Y energy until Y > X. Then I spend the other half of X to slow back down to the initial reference frame and now I have more energy than I started with My guess is that the fuel requirement to maintain cruising speed in spite of the drag exceeds the amount of power you can store @pmdj in any case, the next time my partner complains about the temperature in the apartment I'll just tell them to accelerate up to a more substantial fraction of the speed of light @drewdevault Energy is mass, whether it’s stored in a battery or something else doesn’t matter - it increases the work required to accelerate. And you’ll find that that difference is conveniently >= any “free” energy you thought you gained by “exploiting” blue shift. @drewdevault @pmdj Wouldn't you just harvest energy that would otherwise be absorbed by something else? So you're not creating free energy, you're "stealing it" from surroundings? In non-relativistic speeds i would imagine e.g. a lawn sprinkler, you can either stand and get showered by "your dose" of droplets, or you can run around (imagine very very fast) and collect a lot more droplets than would have hit you while standing. I'm not a physicist though so forgive me if i'm saying nonsense. @drewdevault You're right that it's basically drag. What you're describing is equivalent to trying to extract energy from the still air around you by running while holding a wind turbine. Sure, the turbine will start spinning and can be used to charge a battery, but this energy is coming from your own motion. For the CMB, you can calculate the amount of energy gained from a blueshifted photon and find that it exactly matches the kinetic energy you lose from the momentum it imparts on you. |
@pmdj what stops me from strapping solar panels to the front of a spaceship, accelerating into the CMB at relativistic speeds, then slowing back down and enjoying my free energy stored in some batteries?