E=mcÂ²

GCNRevenger · 2004-03-25 14:15:31

That is a question without a clear answer Errorist...

I would personally say that it has no REAL mass, even though it does ACT like it, that is, it can produce a gravity field. In any event, if the photon has mass or not isn't particularly relivent to your linear laser rocket, the question is how efficently can a given amount of energy push your reaction mass. This depends on the efficency of your power source, the efficency of the laser, and most importantly how the laser light photons make the gas molecules move in a controlled fasion.

And the answer is, not very efficently, by the way.

ERRORIST · 2004-03-25 14:18:35

So how fast will a H2 ion travel when it is hit with a 1 Mw laser inside such a tube by the time it exits? Assume it is the only ion in the tube.

GCNRevenger · 2004-03-25 15:10:51

*Bzzzt* read past posts... you haven't given enough information.

ERRORIST · 2004-03-25 15:20:27

Use your imagination! Best case vs worst case.

GCNRevenger · 2004-03-25 15:43:01

My first instinct, because the proton (hydrogen ion) is very much smaller than the amplitude of the light, there will be ZERO acceleration.

C M Edwards · 2004-03-25 16:50:03

I think we should try another tack.

Errorist, I believe your analysis of the mass-energy equation is insufficient to prove your point. Use of units is an adopted convention, and needn’t necessarily reflect reality, but it is the convention in which the mass-energy equation was derived. You can’t get rid of it without voiding a key assumption.

To really argue your point, it might be best to forget E = m c^2 and appeal directly to Mother Nature.

Nuclear fission and fusion, as well as antimatter annihilation, produce energy by the conversion of mass. Electron spin releases energy spontaneously (and without exhaustion – electron spin doesn’t run down) via quantum transitions. However, I think you’ll be more interested in processes that produce mass – or mass effects – from energy.

One example is Inertial Frame Dragging. This is one of the confirming observations of General Relativity, and is the effect used to explain a boost to the orbital precession of Mercury, Mars, and other planets. As it turns out, the sun’s rest mass alone cannot account for its gravitational field. A small portion is due to the energy of its internal reactions (energy creating gravity), and another small portion is due to its angular momentum (angular momentum creating gravity). It’s referred to as frame dragging because the contribution isn’t all in one direction. The energy of reactions contributes a new outward component (swamped by the mass contribution) and the angular momentum contributes a net sideways component. This sideways component of the sun’s gravity nudges the planets’ precession to such an extent that relativistic corrections are necessary for the orbital mechanics computations for a journey to Mars.

The implication is that energy creates gravity, just like mass.

Another example is the momentum of light. The impact of light on an object creates a slight thrust, as well as imparting other energy. Solar sails are supposed to take advantage of this for propulsion.

This implies that energy has momentum, just like mass.

Another example is the Sysiphus effect, seen in the sub-Doppler laser cooling used to cool atoms to absolute zero temperature. The laser light’s photons exchange momentum with the atoms, slowing their motion, but the recoil of photon impacts on the atoms should set a lower limit for how low their temperature can get. The lowest thermal energy attainable for each atom should be related to the energy of the photons slamming into it, but it isn’t. Instead, it looks like the atoms are able to undergo quantum transitions at lower energies than the photon energy, particularly when the reaction rate (the slamming about by photons) exceeds the rate at which the atom can emit photons of its own. This can create a net energy deficit on the scale of a single atom (i.e, lower temperature), even though the atom mainly only emits at its driving frequency (the frequency of the incoming light). The outgoing energy slightly exceeds the incoming energy for each atom, but only when it’s driven faster than it would normally emit. The difference in energy is related to the frequency of interactions between atoms and photons, and not to the total energy involved.

This strongly suggests than energy has quantum uncertainty, just like mass.

And then there’s pair production from gamma rays. Gamma rays of sufficient energy can transform spontaneously into free electrons and positrons. In this case, a massless photon forms two or more massive particles, just by virtue of having sufficient energy to do so. Furthermore, the resulting positrons and electrons are attracted to each other. If they contact another free particle, they can transform right back to a photon, but the transition can also happen spontaneously for a high enough energy electron, just like it can for a high enough energy photon. For an example, check this out:

[http://www.hep.princeton.edu/~mcdonald/ … e1202.html]http://www.hep.princeton.edu/~mcdonald/ … e1202.html

This implies that matter and energy are not just convertible but equivalent and interchangeable – that mass, fundamentally and of its nature, is a form of energy.

ERRORIST · 2004-03-25 19:03:15

CM,
Very neat article colliding electrons with photons. I think the same holds true for H2 or He ions even though they are much more massive. I noticed they mentioned head on linear collisions in the article. The thought I came up with was linear collision from behind. How much velocity would this give the ion since it would be hit millions of times from behind????? It would be the opposite of what the article mentions, like a million ping pong balls hitting a mack truck from behind but each ping pong ball is traveling at the speed of light. How much would the Mack truck increase its forward velocity????

GCNRevenger · 2004-03-25 19:17:50

No, it won't work for hydrogen ions because they don't absorb photons like electrons do, and hitting a helium atom like that would just cause the electron to fly off and make some alpha rays along with the effect listed here.

It would still only achieve a small velocity, or a small number would achieve any velocity, if any.

ERRORIST · 2004-03-25 19:49:04

So, who wants to absorb the photons? It may be better if they bounce off.

GCNRevenger · 2004-03-25 22:15:17

Because of the wave nature of the photon, if they aren't absorbed, they will just pass around whatever particle you aim them at.

ERRORIST · 2004-03-29 13:08:48

Then why do they collide with electrons in the experiments? The proton is much more massive than the electron!

Earthfirst · 2004-03-29 13:16:31

y not just increase the speed of light speed limit then you could go faster, that what they did with the freeways and such, 55 mph to 75 mph. It's easys.

ERRORIST · 2004-03-29 13:22:32

What happens when the spacecraft is traveling at the speed of light, and you turn the head lights on would it still be dark in front of the spacecraft? I think not. It will illuminate whatever is in front of the spacecraft, which means the light is now traveling greater than the speed of light.

John Creighton · 2004-03-29 13:37:02

You can't travel at the speed of light. Even if you had a warp drive there is probably a better way of thinking about it then FTL.

ERRORIST · 2004-03-29 13:39:58

Still, how fast would the light travel when you turned on the head lights?

John Creighton · 2004-03-29 13:44:55

It would travel at the speed of light no matter what reference frame it was viewed from. However the frequency of the light would look different from each reference frame (see the Doppler effect).

ERRORIST · 2004-03-29 13:54:16

I don't believe that. If I threw a baseball at the moon from the shuttle traveling towards the moon, the ball would get there before the shuttle as long as I threw a strike.

SBird · 2004-03-29 13:58:45

IF you could go at the speed of light, the answer is unknown. The math involved simply doesn't support such a question.

If you were going almost the speed of light, and switched on headlights, you would see the photons going away at the speed of light. An observer watching you would see the photons going just a tiny bit faster than you, slowly pulling away. The rason for this discrepancy is that your are now time-dialated - time slows down for you. Therfore, light seems to be leaving you at teh same speed. This is how special relativity works - light always goes at the speed of lihgt, no matter what frame of reference you're in because time and space warp themselves to compensate. More accurately, you are cutting through spacetime at a different 'angle' but that's a hard concept to visualize.

SBird · 2004-03-29 14:11:04

ERRORIST - it's responses like the last one that make talking to you such a complete waste of time. Relativity and time dialation effects are well known and measured. If they didn't happen, GPS wouldn't work properly, gold would look like silver, mercury would be a solid at room temperature, Mercury's orbit wouldn't precess and gravitational lenses wouldn't occur.

If you want to keep sticking your head in the sand and ignore vast quantities of scientific evidence because you can make some asinine analogy using baseballs, I think we'd all appreciate it if you did it on your own time and would quit wasting ours. If you are just too damn lazy to spend an hour reading any number of well-written explanations of relativity or quantum physics you can find on the Internet through Google or to buy a $3 used book and read it, don't expect us to waste our time debating with you.

Newtownian physics is WRONG. It was proven to be wrong a hundred years ago. Even if parts of Einstein's relativity and quantum physics are proven wrong, the effects like time and space dialation, relativistic momentum corrections, wave-particle dualities and quantum uncertainty have been proven beyond a doubt. Comparing a baseball to a photon is like believing in a flat Earth or epicycles. If you don't want to believe in modern physics, feel free but please quit spamming the boards with it.

ERRORIST · 2004-03-29 14:26:26

It is not spamming it is just an opinion, a right we all have in this country. It is good to have debate it leads to other thoughts which can increase knowlege. And yes mercury could be a solid at room temperature if the room temperature was decreased.Why waste money on the books if I can learn on the internet? BTW try to use better words to make your point.

SBird · 2004-03-29 15:57:07

ERRORIST, I have no problem with new ideas and discussion but that not what you're doing. You come up with wacky ideas off the top of your head that don't work. Then we explain why they don't work and you don't even bother to properly read our responses before going off on inane and incorrect rebuttals.

You clearly have 0 grasp of quantum mechanics or relativity and yet keep insisting you know what you're talking about. You don't! Multiple people have referred you to print and internet resources for learning this stuff and put a lot of effort to write long and informative posts here on the boards to try and help you out and you have ignored all of them.

I just did a search on 'relativity' on Google and immediately found over 10 tutorials on the first page. You can't bother to get a $3 used book or even to do a brief web search to educate yourself. You don't even bother to learn anything from the hard work people on these forums have put in to try and help you out. Then you keep spamming multiple, redundant threads of discussion about stuff that people have already explained and/or disproven. That's not a discussion, that's just plain rude.

Yes, you have a right to keep posting opinions and ideas all over the discussion board, blatantly ignoring concerned efforts to help you out. However, we also have the right to ignore you and to ask you to please stop.

Here's the score, ERRORIST. You know squat about modern physics. If you want to post ideas about space pipelines and laser-ion drives, that's just fine. In fact, I'm glad that you want to put new ideas up here and discuss them. The problem is that you ask for our opinions about these ideas and then promptly ignore everyone. Disagreeing in a rational manner with someone is fine. Ignoring several other people who know far more about physics than you and posting for weeks about disproven ideas is just annoying.

Either put your money where your mouth is and try to learn at least some of the physics involved *or* accept that other people here know far more about physics than you and respect that knowledge *or* let your ideas drop if there's no acceptance of them.

ERRORIST · 2004-03-29 20:36:45

I agree with you once I have asked all that I feel is appropiate, and can't go any further then I will stop unless I think of something else that may work. BTW I like all of you guys and thanks for education it is helpfull!!! Even if you call me names I don't care.

GCNRevenger · 2004-03-29 20:51:57

Ummm no Errorist, it is not when you run out of questions (and rebuttles), but rather, when you learn that your physics application is flawed and come up with a solution. The "can't go any further" in science is when someone finds one flaw the first time, after which you must fix your theory.

ERRORIST · 2004-03-30 07:04:04

Thats correct theories are not concrete. There are to many variables to give a correct answer.

GCNRevenger · 2004-03-30 07:10:09

SOME things, like Relativity (time dialation, apparent mass, etc) and much of Quantum Mechanics is proven though beyond any reasonable doubt. There are many variables to manage for a somewhat accurate calculation of your ideas, but we don't need to do detailed math because it is so clear and obvious that this simply isn't going to work. The basic physics says "NO", so how about you tell us why basic physics is wrong?

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#76 2004-03-25 14:15:31

Re: E=mcÂ²

#77 2004-03-25 14:18:35

Re: E=mcÂ²

#78 2004-03-25 15:10:51

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#79 2004-03-25 15:20:27

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#80 2004-03-25 15:43:01

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#81 2004-03-25 16:50:03

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#82 2004-03-25 19:03:15

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#83 2004-03-25 19:17:50

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#84 2004-03-25 19:49:04

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#85 2004-03-25 22:15:17

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#86 2004-03-29 13:08:48

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#87 2004-03-29 13:16:31

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#88 2004-03-29 13:22:32

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#89 2004-03-29 13:37:02

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#90 2004-03-29 13:39:58

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#91 2004-03-29 13:44:55

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#92 2004-03-29 13:54:16

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#93 2004-03-29 13:58:45

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#94 2004-03-29 14:11:04

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#95 2004-03-29 14:26:26

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#96 2004-03-29 15:57:07

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#97 2004-03-29 20:36:45

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#98 2004-03-29 20:51:57

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#99 2004-03-30 07:04:04

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#100 2004-03-30 07:10:09

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