Can matter be completely converted to energy as suggested by E=mc2?

[Dale]

Is it the real spin of physical quantities or the description of the inexplicable angular momentum of a single particle?

I disagree that they are fundamentally different. Should we have different names for the linear momentum of an electron and the linear momentum of a baseball?

In general, this is another reason why terminology is not clean. Different people have dramatically different ideas of what terms are "good". Some people still like and use "relativistic mass", for example. As I said earlier, it is a big and uncoordinated committee, and there is no enforcement or arbitration body.

 

[Frame Dragger]

But the electron IS an 8-ball. Why do you think it has a white spot with a black center? And if you knock one into the corner hole (nucleus) you win the game (start a _______ reaction).

And it's pronounced kwork.

1.) ROFL. Good one. You win this round you billiard bravo.

2.) It's pronounced however the hell James Joyce did when he was drunk or brilliant enough to write Finnegan's Wake. I think the pronunciation of a nonsense word made to substitute for "quart" should be in line with "kwork" as in "kwort", but since it's a nonsense word don't you think one of (if not) the fundamental building blocks of matter deserves better? ;)

EDIT: DaleSpam: Well, we know particles have angular momentum, but it doesn't seem to arise from the rotation of the body about a center in the manner of a baseball. People ARE going to learn mechanical physics before SR/GR/QM, which means Spin will be preloaded with concepts and meanings that may WORK, but are not truly applicable in reality. I agree that this is the result of the comittee nature of academia, and that my view is not the only one (nor is my passion unique) leading to... a total stalement in the nomenclature of most of modern physics. Barring necessity, it will stay the same and simply be a source of friction on the system, draining efficiency and radiating heat/chaos.

 

[Frame Dragger]

People still refer to the 1905 paper by Einstein on a regular basis, and I answered a question just yesterday with reference to an 1851 experiment by Fizeau. Like it or not, science is a very historical subject. A well-constructed experiment performed more than one and a half centuries ago or a brilliant theory conceived more than one century ago are still relevant today. That entails a lot of baggage. Especially as today's scientists are trained by the previous generation of scientists who coined terms that are still in use today despite dramatic changes in the theory.

I actually like the term "quark" precisely because it is unambiguously new and not likely to ever be mistaken for any other concept.

You might be right about Quark however... it is unlike spin in that it has a unique place. I would use it more as an example of how the nomenclature is completely nonexistant. I suppose the Quark could do worse than have Joyce's single truly incomprehensible book as its namesake.

As for history... what you've said is true of many disciplines and sciences. If a standard pool of termninoligies and nomenclature was established from which any given physicist could draw upon, then history would be irrelevant as far as the linguistics went. It's called a recnciliation process, and lots of other sciences and disciplines do it on a regular basis. As for terms such as the "Hamiltonian of a system" or "Lorentz etc..." they don't need to be changed. Anything that would clarify their definitions would be at least a sentence long. Spin and some other concepts however reflect the messy thinking that led to analogy, and not just a matter of linguistics and efficiency.

 

[Dale]

Barring necessity, it will stay the same and simply be a source of friction on the system, draining efficiency and radiating heat/chaos.

An apt analogy.

 

[Char. Limit]

Now you must answer my questions three, ere the other side ye see...

What is color charge?

What is billiards?

What is the capital of Assyria?

 

[Frame Dragger]

Now you must answer my questions three, ere the other side ye see...

What is color charge?

What is billiards?

What is the capital of Assyria?

What is colour charge?: Answer: Quarks posess a quality described as colour because it has three aspects like the primary colours (R,G,B). Colour forms the distinction between quarks such that they don't violeate Pauli's non-exclusion principle. It also is central to the study of Confinement ("Colour Confiment) in the ineractions between quarks and gluons in a Hadron jet.

Billiards is also known as, "Pool" in which balls of vulcanized rubber or lucite are struck with sticks so that they interact through various physical properties to allow for impressive angles and "shots". The purpose of each variation of the game varies, but in each case the object centers around the manner in which balls must be sunk into one of 6 holes or "pockets".

The Capital of Assyria is... Monty Python ;). And Ninevah when it existed. Here's a question for you... what poem made Abyssinia a popular word? I wonder if the "nin" in Ninevah is related to the cuniform and akkadian "nin". Probably given the locale. I'm too lazy to check from anything but memory however.

Oh, and Which flies further, a laden or unladen swallow? AND DON'T ASK "African or European" I WANT FIGURES! lol

 

[Frame Dragger]

Am I the only one who looks at the title of this thread and thinks, "Hmm... Understanding The Photon: How You and The EM Quanta Can Find A Love Match" lol

 

[Char. Limit]

Yes, and the answer is unladen, by .7 km

 

[Frame Dragger]

Yes, and the answer is unladen, by .7 km

Damn, you answered in metric so I have to concede. You may pass. Other acceptable answers would be Avogadro's Number in nm, 1 AU, or a Cubit. :)

 

[Char. Limit]

Oh, and don't worry. I know what pool is, just not what billiards is.

I shall pass now.

 

[Frame Dragger]

Oh, and don't worry. I know what pool is, just not what billiards is.

I shall pass now.

At this point in time, the terms "pool" and "billiards" are completely interchangable. They all refer to the sets of games. Pool is a term of American origin, whereas Billiards is British in origin. However, both are very commonly used in the USA at least. Snooker as a particular game is probably the only variation which is unsual in the USA.

Wow, we're REALLY far from photon huh?

 

[Char. Limit]

Not really, as photons, being massless, would make just excellent billiard balls. Just think of our distance from the topic in a sine wave: we're far away now, but we'll get back.

You could also think of it as a cosine wave. But not a tangent wave.

 

[Al68]

Is it the real spin of physical quantities or the description of the inexplicable angular momentum of a single particle?

I disagree that they are fundamentally different.

I'm reluctant to comment here, but it seems like a huge fundamental difference to me. Macroscopic angular momentum is nothing more than a function of the linear momentum of an object's constituent particles.

I would think macroscopic angular momentum is fundamentally the same as particle linear momentum, and completely different than particle spin. It's my (limited) understanding that particle spin is an intrinsic property and absolutely not a rotation of its "parts" about its "center".

And, as is the case with most of QM, it's unclear to me exactly how far analogies to various classical concepts are supposed to be taken, so I could easily be way off the mark.

I just hope I don't have to think too much about quark flavor and color. (Correct spelling BTW, Frame Dragger. )

 

[Dale]

I'm reluctant to comment here, but it seems like a huge fundamental difference to me. Macroscopic angular momentum is nothing more than a function of the linear momentum of an object's constituent particles.

I would think macroscopic angular momentum is fundamentally the same as particle linear momentum, and completely different than particle spin. It's my (limited) understanding that particle spin is an intrinsic property and absolutely not a rotation of its "parts" about its "center".

I understand your position, and you are correct about the usual source of macroscopic spin. But I still think that spin is a reasonable name; I consider quantum spin to be the same as macroscopic spin on the "if it walks like a duck ..." principle. Spin acts mathematically just like macroscopic angular momentum that is quantized. It has the same relationship to the Lagrangian as macroscopic angular momentum. It can be measured on a given axis. It has the same units. Etc.

The only reason that most macroscopic spin is due to the particle's linear momentum instead of quantum spin is because quantum spins typically cancel each other out. However, in superfluids you can get macroscopic manifestations of quantum spin. IMO, the mathematical similarity is sufficient to justify the use of the term "spin", but the existence of quantized vortices in superfluids really cements the idea that they are fundamentally the same.

 

[Frame Dragger]

I'm reluctant to comment here, but it seems like a huge fundamental difference to me. Macroscopic angular momentum is nothing more than a function of the linear momentum of an object's constituent particles.

I would think macroscopic angular momentum is fundamentally the same as particle linear momentum, and completely different than particle spin. It's my (limited) understanding that particle spin is an intrinsic property and absolutely not a rotation of its "parts" about its "center".

And, as is the case with most of QM, it's unclear to me exactly how far analogies to various classical concepts are supposed to be taken, so I could easily be way off the mark.

I just hope I don't have to think too much about quark flavor and color. (Correct spelling BTW, Frame Dragger. )

I'm with DaleSpam in principle, insofar as the term "spin" when used in the quantum world isn't as eggregious as "rest mass". Spin was named BECAUSE it seems so very similar to spin in the macroscopic world as far as the math is concerned... and what is SQM but math?

Then again, if we used a unique term to describe the spin of particles in common parlance, intelligent folks such as DaleSpam wouldn't NEED to explain these issue to intelligent people like AL68. That is the tangible benefit of formalized nomenclature.

Oh... and if you mean the spelling of colour/flavour/armour/aeroplane vs. color, flavor, armor, airplane... they are both correct spellings. As it happens however, my spelling is HORRENDOUS along with my penmanship. In a fit of irony, I'm extremely good at several forms of calligraphy. That said, when I write the majority of what is technically well written comes from multiple-pass editing... and I rarely do that online out of pure laziness. ;)

 

[DanRay]

What if the photon is not considered a massless matter particle and instead is considered a just energy. The idea of momentum for photons doesn't seem to follow the same rules as momentum for matter. Whenever and wherever light is propagated it seems to take off at c without the need to accelerate. No matter can ever do that and the equations that relate to momentum have no provision for it either. The 'at rest' idea in physics has always struck me as odd but I have always disregarded my gut instinct in favor of realizing that as long as the rules used within this concept are always consistant no harm is done even if "at rest" can't be achieved or even adaquately defined. But the momentum question and the fact that until they interact all photons always move at c, I think makes the question of rest mass undefinable for photons. I realize that often photons are regarded as a carrier of energy that is somehow imparted during propagation and the idea that photons are the energy hasn't had much traction, but I think it makes perfect sense. If E=MC2 is true the resultant energy must be somthing real other than matter and energy that is attached to matter.

 

[sylas]

What if the photon is not considered a massless matter particle and instead is considered a just energy. The idea of momentum for photons doesn't seem to follow the same rules as momentum for matter.

Yes, it does follow the same rules for matter. The rule is:

$$E^2 = (pc)^2 + (mc^2)^2$$​

p is momentum, and E is the total energy.

If the particle has no momentum, then this reduces to E = mc².

If a particle has very low velocity, then p is close to mv, and E is close to mc² + 0.5mv². This is what you are probably used to as the rules for matter, but in fact it is this simplified matter rule which is the one that is incorrect.

If v = c, then you have a massless particle for which m = 0, and E = p/c, which is true for photons.

The momentum of photons is an experimental fact, observed in particle collisions every day.

Cheers -- sylas

 

[Char. Limit]

I think you might be on to something... maybe, instead of a particle (although photons have some properties of particles, don't they?) a photon is just a discrete amount of energy in a wave...

Nope, I'm not a physicist, I really don't know what I'm talking about. I have but one idea... Could the relationship between waves, particles, and wave-particles be like the relationship between metals, nonmetals, and metalloids in chemistry? If you think about it... Metalloids have some properties of metals, and some properties of nonmetals, but neither label is able to describe them. Wave-particles have some properties of waves and some properties of particles, but neither label is able to describe them...

Or do I just sound like an idiot?

 

[Frame Dragger]

I think you might be on to something... maybe, instead of a particle (although photons have some properties of particles, don't they?) a photon is just a discrete amount of energy in a wave...

Nope, I'm not a physicist, I really don't know what I'm talking about. I have but one idea... Could the relationship between waves, particles, and wave-particles be like the relationship between metals, nonmetals, and metalloids in chemistry? If you think about it... Metalloids have some properties of metals, and some properties of nonmetals, but neither label is able to describe them. Wave-particles have some properties of waves and some properties of particles, but neither label is able to describe them...

Or do I just sound like an idiot?

You sound like you're exploring the possiblity of wave-particle duality as a true duality. Remember however, that TCI (The Copenhagen Interpretation) of SQM (Standard Quantum Mechanics) also says that they can be observed as having the properties of one, but not both at the same time, but that yes... they are both wave and particle... now shut and calculate. lol. So no, you don't sound stupid, but you're handling a problem of Physics in the realm of Metaphysics which is the business of Interpretations of SQM.

You don't sound like an idiot to me, in other words, but you don't sound like a physicist. Not a crime last I checked. :)

EDIT: Edited for clarity in main msg body.

 

[Al68]

I understand your position, and you are correct about the usual source of macroscopic spin. But I still think that spin is a reasonable name; I consider quantum spin to be the same as macroscopic spin on the "if it walks like a duck ..." principle.

I don't really object to the word spin being used, I just think there is a very significant fundamental difference between quantum spin and macroscopic spin. But this difference is normally made clear in textbooks, anyway, I think?

Oh... and if you mean the spelling of colour/flavour/armour/aeroplane vs. color, flavor, armor, airplane... they are both correct spellings.

Yeah, I know, it was just a U.S. vs British thing. :!)

 

[Frame Dragger]

I don't really object to the word spin being used, I just think there is a very significant fundamental difference between quantum spin and macroscopic spin. But this difference is normally made clear in textbooks, anyway, I think?Yeah, I know, it was just a U.S. vs British thing. :!)

The truly sad thing is that I'm American! First generation Greek, but that has nothing to do with it. I just happened to be living in Ireland during a critical moment in my education which has lead to pain, confusion and awkwardness since. THANKS FOR BRINGIG IT UP! *runs away sobbing*... yeah so there's that. :tongue2:

 

[Char. Limit]

Even so, I want to understand all of physics... even the parts that make no sense. Of course, the will to do something doesn't make it easy.

The photon disturbs me. It has no mass, yet it has momentum and energy... both of which have mass in their equations. It appears to me to simply be a packet (quantum?) of energy that...

Are photons one of the four almighty force-carrying particles?

Photon:
Has no mass
Energy determined by frequency
v=c at all times

What else is there?

 

[sylas]

Even so, I want to understand all of physics... even the parts that make no sense. Of course, the will to do something doesn't make it easy.

The photon disturbs me. It has no mass, yet it has momentum and energy... both of which have mass in their equations. It appears to me to simply be a packet (quantum?) of energy that...

Are photons one of the four almighty force-carrying particles?

Photon:
Has no mass
Energy determined by frequency
v=c at all times

What else is there?

Which equations do you mean? I've given the basic equation above, which is satisfied by every particle we know: massless, massive, relativistic, slow, all of them. The other thing photons have is quantum "spin".

Photons are the carrier particle for the electromagnetic force. (I don't know what you mean by "almighty".)

Other force carriers are the gluon (strong force), the W and Z bosons (weak force) and (undetected so far, but predicted) the graviton, for gravity.

Cheers -- sylas

 

[Frame Dragger]

Even so, I want to understand all of physics... even the parts that make no sense. Of course, the will to do something doesn't make it easy.

The photon disturbs me. It has no mass, yet it has momentum and energy... both of which have mass in their equations. It appears to me to simply be a packet (quantum?) of energy that...

Are photons one of the four almighty force-carrying particles?

Photon:
Has no mass
Energy determined by frequency
v=c at all times

What else is there?

They're the force carrying Gauge Bosons for the Electromagnetic force. You have Gluons for the Strong (nuclear) force that results in Colour Confinement of Quarks, the W and Z bosons (weak as Sylas said), and then maybe the Higgs Boson and/or a Graviton (speculative on both counts awaiting evidence in the LHC). The Higgs Boson specifically and the Higgs Mechanism in general are theorized to be the source of Mass in other particles.

It should be noted that ALL Gague Bosons are massless Spin 1 particles, and that is a central part of The Standard Model.

 

[Char. Limit]

The equations I was referencing are the only two I know for momentum, which are $$p=mv$$ and $$p=\frac{d E_k}{dv}$$, and the three equations I know for energy, which are $$E=\frac{1}{2}mv^2$$, $$E=mgh$$, and $$E=\frac{pc+mc^2}{\sqrt{1-\frac{v^2}{c^2}}}$$. All of them depend on mass, don't they?

By almighty, I was just emphasizing their importance.

On the W and Z bosons, what's the difference, if they both carry the weak force?

 

[Frame Dragger]

The equations I was referencing are the only two I know for momentum, which are $$p=mv$$ and $$p=\frac{d E_k}{dv}$$, and the three equations I know for energy, which are $$E=\frac{1}{2}mv^2$$, $$E=mgh$$, and $$E=\frac{pc+mc^2}{\sqrt{1-\frac{v^2}{c^2}}}$$. All of them depend on mass, don't they?

By almighty, I was just emphasizing their importance.

On the W and Z bosons, what's the difference, if they both carry the weak force?

In a single word: Charge. If you'd like some good reading, take a look at GUT theories in which the ElectroWeak force emerges from a union of the EM/Weak forces. Fascinating truly.

 

[sylas]

Here are your equations...

$$p=mv$$

This is an approximation which works only for massive particles and non-relativistic v. A more accurate equation for all velocities less than c is

$$p = \frac{mv}{\sqrt{1-\frac{v^2}{c^2}}}$$​

You don't need mass to have momentum. A particle like a photon has m=0 and v=c, and so the above is undefined. It works out to 0/0. A photon has momentum E/c.
​

$$p=\frac{d E_k}{dv}$$

I've never actually seen this before. It works for the approximations for slow particles, but is false in general. With a bit of calculus you can derive a more correct equation from E² = (pc)² + (mc²)² as follows.

$$\begin{align*} p & = \frac{mv}{\sqrt{1-\frac{v^2}{c^2}}} \\ \text{Hence} \; E^2 & = \frac{m^2v^2c^2}{1-\frac{v^2}{c^2}} + m^2c^4 \\ & = \frac{m^2c^4}{1 - \frac{v^2}{c^2}} \\ \text{Hence} \; E & = \frac{mc^2}{\sqrt{1-\frac{v^2}{c^2}}} \\ \frac{dE}{dv} & = \frac{mc^2(-2v/c^2)}{-2(1-\frac{v^2}{c^2})^{3/2}} \\ & = \frac{mv}{(1-\frac{v^2}{c^2})^{3/2}} \\ & = \frac{p}{1-\frac{v^2}{c^2}} \end{align*}$$​

$$E=\frac{1}{2}mv^2$$

This is an approximation which works only for massive particles and non-relativistic v; and which considers only "kinetic energy", not total energy.
​

$$E=mgh$$

This is for energy changes in a gravitational field. Photons change energy in a gravitational field in the same way as massive particles -- one of the early experimental confirmations of general relativity.​

$$E=\frac{pc+mc^2}{\sqrt{1-\frac{v^2}{c^2}}}$$

This looks like an error. Omit the pc on the top and it is correct.​

All of them depend on mass, don't they?

No. You've just give approximate forms that apply for massive particles. The general equations work fine whether m is zero or not. IMO the most important single equation is the one I gave earlier.

$$E^2 = (pc)^2 + (mc^2)^2$$

It is expressed in terms of momentum, rather than velocity.

On the W and Z bosons, what's the difference, if they both carry the weak force?

To be honest I'm not sure. I don't know much about the weak force.

Cheers -- sylas

 

[Char. Limit]

Actually, my last equation was an error. Thanks for noticing.

So... if the relativistic momentum equation for a photon is indeterminate... that would suggest to me that the photon's momentum cannot be described. Bah... quantum physics being strange and all, I should have expected that.

Next question: If a photon has no charge, and it can't, how does it carry an electromagnetic force?

Er... a photon has no charge, right?

 

[sylas]

So... if the relativistic momentum equation for a photon is indeterminate... that would suggest to me that the photon's momentum cannot be described.

No... it means photon momentum is not described in terms of mass and velocity. Photon momentum can be described just fine, and it is described as a function of frequency. p = hf/c

Next question: If a photon has no charge, and it can't, how does it carry an electromagnetic force?

It doesn't need charge; it needs to interact with charged particles. Beyond that, I'm not good on the details of carrier particles.

Cheers -- sylas

 

[Char. Limit]

Can you describe massive object's momentum in the same terms, say, by using the de Broglie wavelength or something?

A photon has no charge. Thus, a proton is it's own antiparticle.

Two questions: Is the above statement correct, and if it is, is the reasoning correct?

 

[sylas]

Can you describe massive object's momentum in the same terms, say, by using the de Broglie wavelength or something?

Yes, I believe so.

A photon has no charge. Thus, a proton is it's own antiparticle.

Two questions: Is the above statement correct, and if it is, is the reasoning correct?

It is said that a photon is its own anti-particle; but you can't conclude that from lack of charge. A neutron is a counter example. It also has no charge, but it is not its own antiparticle.

Cheers -- sylas

 

[jtbell]

No... it means photon momentum is not described in terms of mass and velocity. Photon momentum can be described just fine, and it is described as a function of frequency. p = hf/c

And even in classical electrodynamics, the momentum density of an electromagnetic wave can be described just fine in terms of the E and B fields:

http://farside.ph.utexas.edu/teaching/em/lectures/node90.html

 

[Char. Limit]

So, if $$p=\frac{h\nu}{c}$$ works for both massive and massless particles, why don't we use that equation instead? Sure, there's a slight hurdle when first learning about momentum, but the overall understanding would be greater in the long run.

 

[atyy]

So, if $$p=\frac{h\nu}{c}$$ works for both massive and massless particles, why don't we use that equation instead? Sure, there's a slight hurdle when first learning about momentum, but the overall understanding would be greater in the long run.

The hurdle is relativistic quantum field theory. But I like your idea!

 

[Char. Limit]

Well, there's a saying: bad habits are hard to break. If you get fixed on the idea that momentum requires mass, as I did, it's hard to break.

I also support never telling students that you can't take the square root of a negative number. If they ask, don't waffle: tell them immediately about i.

I don't know if it has a name, but there's one of my philosophies.