Boffins have fabricated microscopic sci-fi tractor beams for real The idea of tractor beams, concentrated rays of energy used to trap and move objects at a distance, was first introduced in science fiction. A group of physicists from the University of Adelaide, Australia, and the Université de Limoges, France, however are trying to make them a reality. But don’t get too excited, current …
But ( and I know I'm wrong about this, but that doesn't mean I understand ), if they're massless then the force they exert is their speed multiplied by zero?
Newtonian mechanics (F=mv) applies pretty well at non-relativistic speeds (i.e. anything travelling at under an appreciable fraction of the speed of light). Photons travel at the speed of light (in a vacuum, anyway), so Einstein's pesky general realtivity comes into effect, and those equations get a whole load more terms in them.
And when quantum mechanics finish their service and send you the bill, any attempt to read the amount on the bill in order to write the check will change the amount.
If you have them auto deduct from your account, then the time they remove the money might be before you call for service, but you can prevent that by checking your account regularly.
If you have them auto deduct from your account, then the time they remove the money might be before you call for service, but you can prevent that by checking your account regularly.
Upvote for referencing one of the lesser known complementary pairs.
But ( and I know I'm wrong about this, but that doesn't mean I understand ), if they're massless then the force they exert is their speed multiplied by zero?
Only if you use the 'reduced' version of the energy formula, E=mc^2.
The 'strict' formula from wikipedia is
E=sqrt( (mc^2)^2+(pc)^2 )
Here the (pc)^2 term represents the square of the Euclidean norm (total vector length) of the various momentum vectors in the system, which reduces to the square of the simple momentum magnitude, if only a single particle is considered. This equation reduces to E = mc^2 when the momentum term is zero. For photons where m=0, the equation reduces to E=pc.
and also:
The energy for photons is E = hf, where h is Planck's constant and f is the photon frequency. This frequency and thus the relativistic energy are frame-dependent.
....& there was I thinking I was staggering backwards due to the sudden exposure of bright natural sunlight after leaving my windowless Mission Control at 5pm.
Getting me coat cause the white shit is forever getting closer to falling down at this time of year.
right, with momentum and velocity = speed of light, you can calculate an effective mass or 'rest mass' using the e = m * c^2 formula when the energy of the photon [related to frequency] is known
photons are like a 5th state of matter, one step beyond plasma, matter converted into pure energy. a 6th state would be the 'atomic particle mush' you'd find within a black hole
The thing about the em-drive is that the photons/EM waves are internal, so if (and its a big 'if') it works then it is defying the normal requirement for momentum transfer outside of the spacecraft, etc.
But you can use a light/heat source or radio to act as a (very weak) drive since the emission of radiation has a momentum transfer effect as it propagates away.
Edited to add: Seems the commentards further down the page have already answered as such!
Wasn't there a suggestion that somehow the energy expended was distorting spacetime and effectively moving the centre-of-gravity (or should that be mass) of the the rig such that it appeared to generate thrust ?
Posed as a question, not a statement because (a) I don't know, and (b) I'd like to.
Unfortunately, if you read the link to the paper summary, like so many others nowadays it uses the word "simulation" all over the place.
Just because it can be done when playing Elite doesn't mean you can do it for real ...
(Spoiler alert for oldies: Elite wasn't based on fact)
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