0

Photons are the carriers of the electromagnetic force right? (whatever that means--I can't visualize how a particle carries a force, for me a force is something immaterial)

Can we create a powerful light source capable of exerting a force on air a create propulsion? Therefore lifting some weight against gravity?

If so, how much energy/power would we need?

Thanks!

PedroD
  • 291
  • As for a particle carrying a force, think about an electron absorbing and re-emitting a photon. As the photon goes between particles with mass, it carries the force, if that makes any sense. (Oversimplification, probably, but I hope it helps to illustrate the idea.) – auden Aug 27 '16 at 21:05
  • NASA is looking into it. – garyp Aug 27 '16 at 21:17
  • As Emilio says, in space, maybe, but in the atmosphere laser power is greatly reduced, you can read about NASA experiments athttp://www.nasa.gov/centers/armstrong/news/FactSheets/FS-087-DFRC.html –  Aug 27 '16 at 21:31
  • 1
    "similar to light pressure" Uhm. Identical to light pressure. It's the same thing. – dmckee --- ex-moderator kitten Aug 27 '16 at 23:08
  • There have been experiments trying to launch small satellites into orbit by propelling them using lasers. – Lelouch Aug 28 '16 at 02:08
  • @Lelouch More successfully, test-bed solar-sails have been deployed and used. The Japanese saved a bit of fuel getting a satellite to Venus because of a (fairly modest) boost from a test-sized light-sail. There is no problem with a light-drive in theory but it has a terrible thrust-to-weight ratio if you have to bring your power source with you. – dmckee --- ex-moderator kitten Sep 02 '16 at 01:45

1 Answers1

4

Radiation pressure can indeed be used to power solar sails, but the pressure is minute, so it only makes sense to use it in outer space, where it isn't drowned out by the atmosphere. Generally, most proposals use solar radiation, since it is cheaply available (and can even take you inwards to, say, Venus, if you use it correctly), but the use of concentrated laser power could also work - you'd just need a humongously big laser for it, and in many cases there's easier and cheaper ways to do the same thing.

See the linked Wikipedia page for more details and examples.

Emilio Pisanty
  • 132,859
  • 33
  • 351
  • 666
  • Cool, thanks! I am looking for a possible way that explains iron man's trusters, they seem like something related to light pressure, or ionized propulsion. So far I couldn't find a feasible way of achieving that without gigantic amounts of energy. In a 100% efficient system I would need only so much to lift some weight a given distance (eg: http://physics.stackexchange.com/questions/39281/needed-energy-for-lifting-200-kg-weight). So for a real world system I was expecting to have something like 40-60% efficiency for vertical lifting, but damn I can't see anything... – PedroD Aug 27 '16 at 21:22
  • @Pedro So Iron Man's thrusters actually come from this thing called science fiction and you can't actually build them. They're perfectly happy to discuss them over on [scifi.se] and [worldbuilding.se], but here we keep it to what you can actually build. – Emilio Pisanty Aug 27 '16 at 21:29
  • The thing is, most technology we have today was sci-fi. We don't know what we can build. I wanted to address the issues that avoid us from building this at this moment in human history (eg.: power source, anyway for a 40-60% efficient system the power source doesn't need to be huge). What is avoiding us of having efficient thrusters? – PedroD Aug 27 '16 at 21:31
  • The rule of thumb that is usually quoted is that it takes a megawatt of power beamed to a vehicle per kg of payload while it is being accelerated to permit it to reach low earth orbit. If lasers were very efficient at delivering power to a target through the atmosphere, the military would be using them as weapons, not just as missile guide markers, as they do now. https://en.wikipedia.org/wiki/Beam-powered_propulsion –  Aug 27 '16 at 21:39
  • 1
    @PedroD If you want to ask about the Iron Man thrusters, you can do so on a separate thread - I'm not at all interested in discussing them. I answered your question as posed (despite my better judgement and the inclination to vote to close because of insufficient research and direct you to the Wikipedia page) because the question as posed does stay within known physics. As for Iron Man's thrusters, I think the person to as is Tony Stark himself - they're pure science fiction with no plausible mechanism supplied. Current tech is yesterday's scifi but so is light speed. – Emilio Pisanty Aug 27 '16 at 21:41