Templar 514
Amarr Templars
Amarr Empire
46
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Posted - 2013.11.14 23:54:00 -
[1] - Quote
Aisha Ctarl wrote:Because photons are matter and have mass. Every action has an equal and opposite reaction. I'm sure if you had a precise enough instrument, you could measure the "recoil" of turning a flashlight on.
Photons are neither matter nor do they have mass. They are massless particles, this is why they can travel at c, which is the speed of light in vacuum (~300,000 km/s). However, they do have momentum, which causes phenomena like radiation pressure, which is exploited by solar sails.
It also means that if you had a powerful enough laser cannon, you could actually use it as a propulsion system on a spacecraft. However, due to the incredibly tiny amount of force that photon momentum produces per energy unit (~1 Newton per three hundred megawatts!), this requires insane amounts of energy density for any practical application.
It's the sort of thing that would probably require an antimatter-burning reactor, at which point you'd really build an AM engine for your spacecraft instead since this would provide far superior performance and fuel efficiency- the latter is particularly critical for the incredibly mass-sensitive design of spacecraft (you must haul every bit of fuel/propellant for your trip, even the return leg, assuming no fuel stops).
Cat Merc wrote:That doesn't sound right...
Isn't the reason that photons can travel at the speed of light is because they have no mass?
This is mostly correct. As far as I know, photons are considered to have zero rest mass, which is effectively impossible to determine since it's impossible to make photons stop to measure whether or not they have mass. The "mostly" is because of lolEinstein and lolrelativity, 90% of which goes above my head (practical application of some of the mathematics involved is easy (and happens to entertain me)).
Cat Merc wrote:But even so, it would take HUUUUUUGE amounts of light to actually produce any form of noticable recoil.
This is definitely correct. It takes approximately 300 megawatts  of electrical energy with an impossible 100% efficient energy-to-light conversion in a laser engine to produce 1 Newton of thrust.
ONE NEWTON. For THREE. HUNDRED. MEGAWATTS.
As I noted above, the energy density required for any kind of practical method of using this for a propulsion system would be so high as to require an antimatter powerplant, at which point it's not much of a leap to instead build an antimatter rocket engine for your spacecraft instead. |