Radio Frequency emitter used to propel objects with a parabolic reflector.

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gophert said:
Would you really feel something or would it simply reverse time with each use - essentially keeping Audioguru alive and well on the interwebs forever!
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I experienced "deja vu" one time in my life. I am glad it never happened again.
Something keeps me getting younger every year, I think it is my wife.
 
audioguru said:
I was going to feel the billions of photons coming out of my very bright flashlight so I was careful it didn't blow my hand off. But I did not feel anything.
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that's because the pressure exerted by light is orders of magnitude less than what the OP was assuming... also the specific photon energy plays a big part, x and gamma ray photons exert a lot more force than visible light (but flying a vehicle using high energy x-rays or gamma rays for propulsion might be a bit problematic... some of the same problems as the nuclear powered bomber projects back in the 1950s)

photon energy is inversely proportional to wavelength, so using radio waves would be extremely inefficient. even with visible light, the amount of light required to lift a baseball off the ground would probably burn the baseball to a cinder
 
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unclejed613 said:
all of the real math associated with radiation pressure can be found here: https://en.wikipedia.org/wiki/Radiation_pressure
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interesting to think about...
(I haven't thought of the answers, just the questions. And I only looked at the pictures in the Wikipedia article)
- does an absorbed photon (e.g. black surface) cause more momentum than reflected photons?
- what happens when a UV photon is absorbed by a phosphorescent surface, then some seconds later, emits radiation of a slightly longer wavelength. Does the emitted photon add to the momentum as recoil?
 
Might try this with my grandkids, should be fairly easy to balance a balloon on the end of a torch beam. They'll be very impressed.

Mike.
 
gophert said:
reflected photons?
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IIRC from the 70's: Technically, photons are not reflected; they are absorbed and re-emitted, which is why/how the polarization can change. The emitted photon always has less energy, manifesting as being "dimmer", a frequency shift, etc.

ak
 
AnalogKid said:
And that is why phosphorescence and reflection are two different physics.

ak
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Very true

Another true statement: either your memory or your source of information from the 1970s is crap.
AnalogKid said:
IIRC from the 70's: Technically, photons are not reflected; they are absorbed and re-emitted, which is why/how the polarization can change. The emitted photon always has less energy, manifesting as being "dimmer", a frequency shift, etc.
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When a military jet fighter uses its "afterburner" for maximum thrust then maybe it is the red photons that produces the tremendous thrust??
A similar thing occurs when a sports car has a turbo that glows red when the turbo power is maximum.
 
AnalogKid said:
Not a "Most Helpful" response.

ak
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Sorry, the claim was so outrageous that I don't really feel like writing out how physics of reflection vs absorption vs scattering works. Here is the more helpful response. Google "physics of reflection".

Also, look up splitting laser beams and what happens if you divert one beam through several mirrors then recombine with a non-reflected beam (or less reflected beam) you'll not see any interference patterns or other evidence of color shift so you'll know - both beams have the same wavelength. Still trying to understand your claim of a photon "dimming" but no need to explain.
 
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audioguru said:
Propelling objects with photons or radio waves. Hah!
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Actually, photonic propulsion - light sail or solar sail - is a tested and possibly practical system for small unmanned spacecraft.
It's just that the effects are orders of magnitude smaller than the OP was claiming.

At the same distance from the sun as the Earth, a light sail provides about eight newtons force per square kilometer of area.
Very little in absolute terms, but zero fuel needed & that force is continuously available, which adds up in velocity terms over time.

Various tests have been done in space over the last ten years or so to verify the effect and the amount of force possible.
 

And as used in countless SciFi over the years (The Mote In Gods Eye would be a classic example - where it's also accelerated faster by a HUGE laser).

However, as well as requiring MASSIVE sails it also only works in a vacuum.
 
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