How would an infinitely powerful laser act?

[Cyparagon]

Well, there's a Crookes radiometer and there's a Nichols radiometer. The former has white/black vanes and operates because of heat. The latter has silvered mirrors and measures actual radiation pressure.

 

[Things]

As for an infinite powered laser, apart from absolutely destroying pretty much everything, it's beam would consist entirely of plasma as it ionizes the air. So technically you'd end up creating a huge plasma ball in the beam path until you completely ionize all gasses on earth.

So, what would really happen? We'd all die. Simple as that

 

[Wolfman29]

Interestingly, I actually don't think that any of that would happen. I think you would attempt to turn it on and it would instantly create a black hole and no light would be emitted further... we'd all die anyway, but in a different manner ^_^

 

[NickD070]

My interpretation would be that since the laser is infinity powerful it would instantly heat everything in it's path to, well almost infinite temperatures. Quickly after the matter in the path of the laser turned into ionized plasma it would break down into a quark-gluon plasma (at about 4 trillion degrees celsius). This is where the particles that make up protons and neutrons split into the basic quarks and gluons that hold them together. And obviously since that plasma would be far hotter than the interior of our sun the entire earth would last only seconds before being destroyed.

And even that scenario is a modest one because the energy released in the big bang was not infinite. If the energy released by that laser was infinite the effects would be infinitely greater.

 

[chipdouglas]

If we are talking about an infinite laser, then I assume you'd need an infinite power supply. So my theory is that the infinite laser would never exist because all the infrustructure would take up all the space on earth. Leaving no room for us to live. Then we would get frustrated and scrap the project.


Michael

 

[NickD070]

The US government isn't afraid to spend ridiculously large amounts of resources to build something with little foreseeable uses. Heck, they'd probably build two. :crackup:

 

[NickD070]

We could probably power the laser with some of those cheap 18650's coming out of certain regions. At the rate the claimed "mah" is increasing it shouldn't be too long before they claim the batteries have an "Infinite mah" capacity.

 

[joeyss]

You guys are forgetting...infinite laser power means the reflections are infinite two....so that means as soon as you turn it on the reflection will just destroy the laser.

 

[NickD070]

Well sure. The descriptions of what would happen are all in good fun. We have to ignore a lot of other facts and scientific principles too like the whole "infinite" thing which would be imposable.

 

[Teslanium]

Disregarding the "infinite" variable, a powerful laser might actually behave as a "photon rocket engine" and propel itself, but only in outer space, as the thrust level would be extremely low and would have to run a very long time to gain any measurable, if not useful velocity. Similar to an ion engine but a lot worse.

It is well known that the light from stars pushes away gas and dust (over VERY LONG time frames), producing "bubbles" of clear(er) space around same.

T.

 

[Cromagnum]

Photons do have a mass, albeit very very small as others have said. If you could have an infinitely high concentration of them coming out of the laser, it's conceivable that their combined mass could be higher than that of the laser + host. But then again, the thing would probably get so hot there wouldn't be material with a high enough melting point to tolerate it. Haha.

 

[NickD070]

I understand where the confusion comes from but the photon really has no mass. At least not the type of "mass" that is relevant here.

It would be impossible for any particle that travels at the speed of light to have mass. This is a very basic principle of physics. If a photon did have a rest mass it would carry a (dare I use the word) infinite amount of energy.

This can be proven with the formula

Not to mention good ol' E=MC2.

In fact I recently gave a speech at a college on a related matter.

Don't get me wrong I've been wrong before, but Einstein has a pretty good track record. And just about every physicist is in agreeance on the matter.

And just out of curiosity what would be the mass of this "massive" photon?

Sources:
Photon - Wikipedia, the free encyclopedia
Massless particle - Wikipedia, the free encyclopedia
Mass of the Photon
Do photons have mass? | How It Works Magazine

 

[RedDart]

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.

It would look a little something like this :lasergun:

Haha

 

[SirRej]

Light does create some force, albeit small. In space this can be useful for "solar sails".
Check out this video on solar sails:
Sailing in Space - YouTube

 

[NickD070]

Well I'm pretty sure most people on this thread agree that radiation pressure from a laser exerts a force on other objects.
And this radiation pressure is the main force that powers solar sails (The other being solar wind).

I think the disagreement comes from some people mistakenly thinking that a photon has a (rest) mass and that this is what is causing the force on other objects.

 

[Asmodian]

As I understand there is no difference between rest mass and effective mass when calculating the force of a photon hitting a surface.

On a related note doesn't an atom in an excited energy state (as if just hit with a photon) have a higher mass than one at the ground state?

Wikipedia based napkin math for the momentum of a single 445nm photon.

p = h/lamda
p = 6.62606957(29)×10^−34 J*s / 4.45*10^-7 m
p = ~1.49x10^-27 (J*s)/m
p = ~1.49x10^-27 kg*m/s

445nm photons
E = hc/lamda
E = 1.98644568×10-25 J*m / 4.45x10^-7 m
E = 4.464x10^-19 J
given a 2W beam for 1 second
2 J*s/4.464x10^-19 J = 4.480x10^18 photons per second

p = 1.49x10^-27 kg*m/s * 4.480x10^18 per second = 6.67x10^-9 N = 1.5x10^-9 lbs

So a two billion watt 445nm laser would apply 1.5 lbs of force to an object (or thrust for a spacecraft )? Can anyone tell if I went wrong?