Science a GoGo's Home Page Forums General Discussion General Science Discussion Forum Infinite divisibility

I read that some physicists think that you can can divide any particle into other particles (including quarks) whilst others think that a particle that cannot be divided exists.

Do you think that every particle in existence can be divided into smaller ones? single choice
	yes
	no
Votes accepted starting: 01/01/70 12:00 AM You must vote before you can view the results of this poll.

1/2 a neutrino is nonsensical.

When we have evidence otherwise ... I'll change my opinion.

Principle of charity, DA. I think Rob means that all particles are comprised of even smaller particles.

I understood what he intended.

But lacking evidence that such exists such discussions are as meaningless as my invisible purple rhinoceros.

As I said ... the day someone figures out a logical meaning for 1/2 a neutrino or 1/2 a photon ... I will embrace the possibility.

An open mind is important. But an open mind does not mean believing in invisible purple rhinoceri.

What's the mass of a photon? It's not zero, I remember that much. So just divide that mass by two. Now, this new number that you have cannot be the mass of a photon, it has to be the mass of something else. Right?

Errr...?

Does invisible purple rhinoceri = things we cannot possibly know thus are not worth the energy discussing or thinking about? I think so.

They are kind of like road blocks. The road blocks that protect travelers from driving off the cliffs of insanity.

I'm going to picture them from now on as protective giants, these purple things holding signs with big orange letters, "YOU SHALL NOT PASS!"

Leptons are point particles. The lowest mass leptons in any family have neither internal strucure nor anywhere to go smaller. They do not decay and they cannot be composite particles.

Rob wrote:
"What's the mass of a photon? It's not zero, I remember that much. So just divide that mass by two."

Neutrinos have a mass expressible with the use of numbers. That does not make them divisible.

Pi = 3.1415926...

Divide it by 6.293 and you will get a result. A totally meaningless result.

Some theorist believe that space is quantized on a much finer level than we are accustomed to thinking about. If this turns out to be true, then even "elementary particles", e.g., leptons like the electron, may well have structure. Structure usually means: "it has parts." These theorist are speculating on ways to unite quantum theory and gravitation theory and the final word is far from in. There are several theories and the one that I have in mind is called Loop Quantum Gravity or LQG for short.

Have a look at this for starters

http://en.wikipedia.org/wiki/Loop_quantum_gravity

A book on the subject is: Three Roads to Quantum Gravity by Lee Smolin. This is a popular treatment of the subject.

Right. I've been monitoring the results of this poll and it seems that a lot of you believe in a non-divisible particle. Answer this; can a particle that has zero mass exist?

The photon - any photon, all photons - have zero rest mass. The photon is the virtual vector boson for electromagnetism, and that is infinite in range. The graviton - if it existed - would have zero mass. The graviton would be the virtual tensor boson for gravitation, and that is infinite in range. All infinite range forces, if they have quantized propagators, must have zero rest mass quantized propagators.

Rob this may come as a shock to you ... but science does not work by, and nature does not conform with, the expectations of the many.

And, of course, what Al said ... but you are confusing things. Zero rest mass has absolutely nothing, nada, zilch, to do with whether something is divisible.

so what proof is there that a photon is a particle and not a wave?

Rob asked "so what proof is there that a photon is a particle and not a wave?"

I don't know if "proof" is the right word to use since physics is not math. In math all that is needed is logical reasoning. In science we need to used inductive reasoning. But you were not asking about method, so ---

In the 1880s Hertz was trying to produce the electromagnetic waves predicted in Maxwell's electromagnetic theory. He noted a pesky effect interfering with his experiments. He observed that electrodes should be cleaned frequently to avoid the problem and suggested that someone look into the physical basis the problem.

That got done by Philip Lenard in 1902 and is now called the photoelectric effect. Lenard's efforts were experimental and quantified the effect without offering an explanation. It was totally inexplicable on any classical basis. A real head scratcher, in fact.

Three years later Einstein developed a theory that accounted for all the odd info concerning the effect. He used the quantum of action discovered by Planck in 1900 and the assumption that light is composed of discrete quanta. (These quanta are now called photons, after G. N. Lewis 1924.)The theory was regarded with caution at first, but it works and gives one of the first insights into the explantion of a whole bunch of head scratchers. It was the first quantum theory of anything.

From an inductive point of view the whole idea of a photon works. That's all the proof that you get that light is a particle.

As for showing that light is not a wave. Well that's just not true. Particle - wave? Wave - particle? To really do this question justice we would need to conside duality/complementraity and the correspondence principle.

dr_rocket wrote:
"Rob asked "so what proof is there that a photon is a particle and not a wave?"

I don't know if "proof""

And quite frankly there is none and never will be any. Because a photon is not a wave. And a photon is not a particle. And a photon is not some new-age mixture of the two.

A photon is a photon is a photon. All of these words like "wave" and "particle" refer to analogies in mathematic that help us describe and predict the behavior.

No physical entity changes its form to comfortably comply with our wishes.

A wave can act like a wave and like a particle. A time-independent localised electron-wave has a centre of mass just like a particle, and when observed from an inertial reference frame moving relative to the time-independent wave, the centre of mass will move like a "point-particle". What happens to a photon when it excites an electron? It disappears. This is strange behaviour for a photon is a photon is a photon; suddenly it is a "nothing". What happens is that the photon entangles with the electron wave, thus increasing its energy so that it has to morph, within a time delt(t) as determined by Heisenberg's uncertainty for energy and time, into another atomic orbital (wave).

Now the photo-electric effect: the incoming photon entangles with the electron-wave thus increasing its energy. If this energy is equal to the workfunction, the electron-wave morphs into a free electron wave that is stationary relative to the metal substrate. If the photon has more energy, the electron wave it entangles with, morphs into a free electron wave with kinetic energy relative to the metal substrate. You do not need "particles" colliding; every interaction can be described in terms of waves entangling, or waves that superpose. A photon is a wave, a wave a wave, which can change its shape and size. Only its energy is quantized NOT its locality. It has to localise in order to entangle with an atomic electron wave.

The quantum-mechanical energy of a free stationary electron wave is its mass; i.e. it has potential energy. Thus solving a wave equation (whether Schroedinger's or Dirac's) by setting the potential energy of a free electron equal to zero, is a futile calculation. You must have a potential energy term that accounts for the rest mass of the electron. The energy of an atomic electron orbital is thus less than the rest mass of the electron. The difference is the energy required to set the electron free and ionise the atom.

I was talking about matter waves; specifically electron waves. Nonetheless, most waves, except a light wave, which move along a single direction, will be stationary within a reference frame travelling with it; for example, if you have non-dissipating water waves which travel along a single direction, and you travel with the waves, you will observe them as being stationary. If the wave is a soliton-wave and you travel with it you might conclude that it is a type of stationary "particle" on the surface of the water. If it is a localised time-independent electron-wave, you might interpret it as a particle "with size" having a centre of mass. When such a wave moves relative to you, it will appear as a particle with size moving as a a particle should; i.e. along the path followed by its centre of mass. Thus although it is a localised field, one would interpret it as a "point particle". The size of a wave is determined by the applicable boundary conditions. When these change, for example when the electron enters a solid material, the localised electron wave can delocalise to spread over the volume of the solid; i.e. it can becaome a Bloch wave.

I would like to be more rigorous but it is difficult on a BB when one wants to make a statement in as short a space as possible.

Johnny Boy wrote:
"I was talking about matter waves; specifically electron waves"

You still don't get it. There is no such thing as electron waves: There are only electrons. Electrons ARE electrons. They are not something else.

This is where we disagree. Electrons are localised waves they are not particles "waving" their tails only when you look for their tails. Try and think outside the Copenhagen paradigm; it is wrong just like Einstein expected. Oh where is Einstein? We need his brains!