A common claim of propellantless propulsion is that you can get a constant acceleration from a constant source of power. This would provide free energy.(*) Propellantless propulsion lets you increase velocity proportional to the energy you put in.(*) Classical physics lets you extract energy proportional to the velocity squared.Possible workarounds:(*) Firstly why not free energy? In for a penny, in for a pound as they say. Also perhaps the energy is coming from somewhere else. To this I would just say: at least stop talking as if the only application is a better ion drive. It is still freaking free energy, man.(*) How about if it is somehow tied to a particular inertial frame. In this case you have something that is propellantless in the sense of a plane with a propeller. You won't get the same advantage but it could still be way better than a rocket which requires exponential amounts of fuel to achieve a given velocity. Another interesting result is that it may also provide a form of free energy, but only the well known type exploited by sailing ships that act in two mediums with different average velocity.
In software a well known rule is garbage in, garbage out. I have the feeling that "constant acceleration from a constant source of power necessarily implies free energy" is ignoring the first term of the likewise rule : free energy in, free energy out.
Quote from: frobnicat on 08/04/2014 01:05 amIn software a well known rule is garbage in, garbage out. I have the feeling that "constant acceleration from a constant source of power necessarily implies free energy" is ignoring the first term of the likewise rule : free energy in, free energy out.No, you're missing the point. Imagine you have a box. You put in one dollar and two dollars come out the other side. Obviously, by cycling those dollars back around, you can make as many dollars as you want. They're free dollars.
That's what free energy means. It means you have a box and if you put X amount of energy in one side, you get more than X amount of energy out the other side. You can just cycle the energy you get back as output into the input and you get as much energy as you want, without limit. That's what free energy means.You need to put some energy in to jump-start the whole process, but after it gets going, you just cycle the some of the output power back to the input and the device runs forever producing power, without any more power input ever needed.
you cannot ever violate the energy conservation law unless you are considering a situation in which the whole global shape of the Universe - its asymptotic behavior at infinite distance - is being transformed. So whatever happens near the Earth will always conserve the energy pretty much exactly, with the deviations' being undetectable.
Around the Earth, as long as you do no cosmic-size experiments, and we won't be able to do them, the spacetime has a time-translational symmetry at infinity because the spacetime is almost exactly flat and with this time-translational symmetry of the background in place, Noether's theorem guarantees the existence of the energy conservation law. So no perpetual motion machines. Again. The violation in cosmology is something like that the total energy carried by dark energy (or photons) increases (decreases) by a factor of 2 in something like 10 billion years. It's significant at the cosmological timescales and length scales but it has no impact on local experiments performed on the Earth.
The standard paradox from being able to communicate faster than light is that...
(*) Classical physics lets you extract energy proportional to the velocity squared.
Quote from: KelvinZero on 08/03/2014 05:06 am(*) Classical physics lets you extract energy proportional to the velocity squared.Where, and how?
Ok, and that has anything to do with spaceflight in the near future (like our lifetimes), how?
Maybe we are working off of two very different definitions of what "advanced concepts" means. The header for the thread states "In-works and future conceptual ideas of space flight, from Nuclear Propulsion to Tethers and beyond". I don't see "free energy, FTL paradoxes, dark energy, wormholes, warp travel, FTL communications", any of that being within that definition.
I think that there are those who take the term "advanced concepts" as an excuse to go off into oogie-boogie sci-fi bordering-on-nonsense that will have no application while any of us are on this earth and long beyond this until several laws of physics can be broken. Of course, if this forum were to be renamed "Sci-Fi Advanced Concepts" I'd go away and never say another word about it.
Isn't this oogey boogy?If my post gets more than five likes, that'll be a yes and a lock. If the opening post gets more than five likes, it stays.Who wins? You decide!