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FrozenGate by Avery

How would an infinitely powerful laser act?

drummerdimitri

drummerdimitri

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Oct 15, 2007
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Hey guys,

I was just thinking about one of newton's laws of motion: "every action has an equal and opposite reaction", and was wondering if that would also apply to a laser.
Would an infinitely powerful laser push itself backwards in the opposite direction of its beam or does that not happen because there is no link between the laser beam and the body?
Assuming such a laser could exist of course.
 





as you are talking about infinite energy, it would quickly destroy the universe

but before it done that, it would probably bend space
 
Photons have no mass so would there be any force to have an equal and opposite force acting back on it?
 
Drew said:
Photons have no mass so would there be any force to have an equal and opposite force acting back on it?
Click to expand...

Photons do have mass so insignificant that we usually ignore it, but I am not sure that would be the case here. Wouldn't more power mean more photons mean more force?
 
Physics interests the heck out of me but its been so long since I've studied it. I do remember that force = mass x acceleration, so more photons should mean more force. I would love a laser with some "kick"
 
Drew said:
Physics interests the heck out of me but its been so long since I've studied it. I do remember that force = mass x acceleration, so more photons should mean more force. I would love a laser with some "kick"
Click to expand...

How awesome would it be to have a laser powered jet pack that propels you and burns the ground beneath you.
 
That would be scary. Reminds me of the scene from Iron Man where he's hovering in the garage around the expensive cars. I don't remember if any of them get damaged or not. It would probably take a cold fusion backpack to power it
 
drummerdimitri said:
Photons do have mass so insignificant that we usually ignore it, but I am not sure that would be the case here. Wouldn't more power mean more photons mean more force?
Click to expand...

How much mass are we talking about? I'm aware of the particle/wave duality (don't quote me on this) in that it's like a particle in that it has mass (like you said, an insignificant amount) but act like a wave in it's actions. Like a light "packet" if you will.
 
Yes, a laser (or flashlight, etc) IS pushed away from the direction the light exists. The force is generally tiny, in the order a few nanonewtons per watt of light emitted.

This mechanism has been proposed for propulsion in space: a lamp on the back of a spacecraft will accelerate it slightly, but has the advantage that it doesnt expel any fuel that can run out.

To actually levitate a laser on earth the power output would need to be enormous: if the whole thing weighs only one kilogram, the power output has to be in te order of 3 gigawatts to break even against gravity.
 
I have to disagree with the notion that a photon has mass. That would violate the laws of quantum electrodynamics.

A photon is a "packet" of electromagnetic energy and electromagnetic energy doesn't have mass.
 
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Photons do have mass, that is why a black hole is black, light can't escape the gravitational field. Gravity only affects matter (stuff with mass).
 
The particle/wave duality you're talking about holds for both photons and other things that do have mass. De broglie came up with the equation lambda = h/p, where lambda is the wavelength in meters and h and p are planks constant and the particle momentum respectively. Basically it says that all matter has particle and wavelike characteristics, so that even objects such as baseballs and cars exhibit wavelike properties but their wavelengths are physically impractical to measure. Do some reading about the double slit experiment, it is a great starting point in trying to grasp the strangeness of quantum mechanics.
 
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Well said ibuprofen!

But also, "black holes" aren't black. You either see the disk of stellar material spinning into the event horizon or of there isn't a disk you see a lensing effect on space behind the black hole.

You see it takes an infinite amount of energy to accelerate a particle with mass to the speed of light. Last I checked my 18650 didn't say "infinite mah"...
 
No disrespect intended though. LPF is a great place to expand one's knowledge base.
 
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