# Propellantless propulsion, apparently.

Discussion in 'General Science & Technology' started by Laika, Sep 8, 2006.

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1. ### Farsight

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Oh I do so. You don't. Show me a photon at rest and I'll agree with your assertion that it has zero mass. My preferred view is that both mass and energy contribute to gravity, a photon has energy, so it contributes to gravity, so we can view that energy as mass. Now we can talk sensibly about the best definition of mass as regards rest mass v relativistic mass...

http://math.ucr.edu/home/baez/physics/Relativity/SR/light_mass.html

"It might be thought that it would be better to regard the relativistic mass as the actual mass of photons and light, instead of invariant mass. We could then consistently talk about the light having mass independently of whether or not it is contained. If relativistic mass is used for all objects then mass is conserved and the mass of an object is the sum of the masses of its part. However, modern usage defines mass as the invariant mass of an object mainly because the invariant mass is more useful when doing any kind of calculation. In this case mass is not conserved and the mass of an object is not the sum of the masses of its parts. For example the mass of a box of light is more than the mass of the box and the sum of the masses of the photons (the latter being zero). Relativistic mass is equivalent to energy so it is a redundant concept. In the modern view mass is not equivalent to energy. It is just that part of the energy of a body which is not kinetic energy. Mass is independent of velocity whereas energy is not...

...but please don't try to pretend that this is not a valid debate via facile attempts to discredit.

Yeah, too right.

Last edited: Feb 8, 2007

3. ### (Q)Encephaloid MartiniValued Senior Member

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Photons are never 'at rest.'

Your 'preferred view' is exactly that, regardless of it not agreeing with observation and experiment.

http://math.ucr.edu/home/baez/physics/Relativity/SR/light_mass.html

"It might be thought that it would be better to regard the relativistic mass as the actual mass of photons and light, instead of invariant mass. We could then consistently talk about the light having mass independently of whether or not it is contained. If relativistic mass is used for all objects then mass is conserved and the mass of an object is the sum of the masses of its part. However, modern usage defines mass as the invariant mass of an object mainly because the invariant mass is more useful when doing any kind of calculation. In this case mass is not conserved and the mass of an object is not the sum of the masses of its parts. For example the mass of a box of light is more than the mass of the box and the sum of the masses of the photons (the latter being zero). Relativistic mass is equivalent to energy so it is a redundant concept. In the modern view mass is not equivalent to energy. It is just that part of the energy of a body which is not kinetic energy. Mass is independent of velocity whereas energy is not...

5. ### Farsight

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3,492
Yeah, yeah, whatever. Observe the text in red and conduct an experiment for yourself:

"It might be thought that it would be better to regard the relativistic mass as the actual mass of photons and light, instead of invariant mass. We could then consistently talk about the light having mass independently of whether or not it is contained. If relativistic mass is used for all objects then mass is conserved and the mass of an object is the sum of the masses of its part. However, modern usage defines mass as the invariant mass of an object mainly because the invariant mass is more useful when doing any kind of calculation. In this case mass is not conserved and the mass of an object is not the sum of the masses of its parts. For example the mass of a box of light is more than the mass of the box and the sum of the masses of the photons (the latter being zero). Relativistic mass is equivalent to energy so it is a redundant concept. In the modern view mass is not equivalent to energy. It is just that part of the energy of a body which is not kinetic energy. Mass is independent of velocity whereas energy is not...

And whilst you're not remotely interested, this is Mass Explained: http://www.sciforums.com/showthread.php?t=61557&highlight=mass explained

Last edited: Feb 9, 2007

7. ### (Q)Encephaloid MartiniValued Senior Member

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Since you point that out, please explain why YOU think the total sum is more than the sum of the individual parts?

8. ### Farsight

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3,492
Huh? I don't think the total sum is more than the sum of the individual parts. If a box of light has a mass of 2 grams and the box has a mass of 1 gram, what I'm saying that the light has a mass of 1 gram. I explained all this in MASS EXPLAINED. You ask me to explain, but at the same time you don't want me to, because you'd rather stick with your 1 + 0 = 2.

The point being that because I understand mass and energy, I don't totally rule out "propellantless propulsion" even though I feel sceptical about SPR.

9. ### (Q)Encephaloid MartiniValued Senior Member

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Since you refuse to learn anything and wish to stick to your silly pet theories, there's really nothing more anyone can say. At the very least, read a book someday.

10. ### Farsight

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LOL, at the very least, answer this question:

Q: If a box of light has a mass of 2 grams and the box has a mass of 1 gram, what is the mass of the light?

Don't you get it yet? I understand mass. You don't want to. And what's sad, is that you'd rather pour bile and insults.

11. ### (Q)Encephaloid MartiniValued Senior Member

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As was said, zero.

No, you don't.

I don't want to follow your silly pet theory, if that's what you mean.

They're not insults, they're observations.

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13. ### (Q)Encephaloid MartiniValued Senior Member

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First, there is this gedanken with explanation:

... followed closely with this:

"You should not use this to justify the statement that light has mass in general."

14. ### TristanLeave your World BehindValued Senior Member

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1,358

"The photon is a massless particle."
Actually, the 'idea' of a particle is something we attribute to a photon. It is also very convienent and correct to treat light like a wave in some circumstances. Hence, Wave-Particle Duality.

Just thought Id throw that in there.

Furthermore, RELAX. Things can be lost in reading words vs a discussion, so its best to explain everything very, very carefully.

And with relativity and light, remember reference frames. If you forget about those, its all meaningless.

Tristan

15. ### Farsight

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Thank you Tristan.

http://galileo.phys.virginia.edu/classes/252/particle_creation.html

"The neutral pion mass is 135 MeV, the charged pions have mass 140 MeV, where we follow standard high energy practice in calling mc2 the "mass", since this is the energy equivalent, and hence the energy which, on creation of the particle in a collision, is taken from kinetic energy and stored in mass..".

In simple terms this is putting light into a box, albeit without the box. Understanding this is crucial to any serious discussion about "propellantless propulsion".

16. ### (Q)Encephaloid MartiniValued Senior Member

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But, do YOU actually understand that photons have no mass?

17. ### Farsight

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3,492
Let's try to be a little more precise shall we?

a) rest mass by definition does not apply to a photon.
b) does not apply is not the same as is zero.
c) a photon has relativistic mass.
d) rest mass v relativistic mass has been an ongoing debate in physics
e) I understand mass, I can explain it.
f) you have no rational argument to counter MASS EXPLAINED
f) An understanding of mass is relevant to "propellantless propulsion"

Now, can we get on please?

Last edited: Feb 12, 2007
18. ### Farsight

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3,492
If we look at the Baez article, we can see that the debate revolves around terminology:

http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html

The old definition of mass, called "relativistic mass" assigns a mass to a particle proportional to its total energy E, and involved the speed of light, c, in the proportionality constant: m = E / c 2.

The modern definition assigns every object just one mass, an invariant quantity that does not depend on velocity. This is given by m = E0 / c 2, where E0 is the total energy of that object at rest... Note, by the way, that using the standard definition of mass, the equation E = m c 2 is not correct. Using the standard definition, the relation between the mass and energy of an object can be written as... E 2 = m 2 c 4 + p 2 c 2

In one sense, any definition is just a matter of convention. In practice, though, physicists now use this definition because it is much more convenient. The "relativistic mass" of an object is really just the same as its energy, and there isn't any reason to have another word for energy: "energy" is a perfectly good word. The mass of an object, though, is a fundamental and invariant property, and one for which we do need a word...

I understand energy and mass, I know how energy equates to relativistic mass and can be tied up as rest mass, how an object is turned into another object and how momentum becomes inertia. It isn't rocket science, after all pair production tells us all that rest mass is not fundamental. I know how the two portions of E 2 = m 2 c 4 + p 2 c 2 are bridged back to E = m c 2, and it pains me to see the confusion created by "modern convenience" coupled with dogmatic hostility.

19. ### (Q)Encephaloid MartiniValued Senior Member

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You still don't get it. Mind like a steel trap, nothing gets in.

No, a debate for people like you who don't understand physics.

You imagine it, from the same place your explanations are derived.

Rational arguments are not used to explain gibberish.

20. ### (Q)Encephaloid MartiniValued Senior Member

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No, what we can see is that you are unable to comprehend it.

You think that's painful?

21. ### Farsight

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3,492
Sigh, do you ever contribute anything apart from insults?

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23. ### (Q)Encephaloid MartiniValued Senior Member

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Just stating the facts, ma'am.