Protons, neutrons etc

Communist Hamster

Communist Hamster

Cricetulus griseus leninus
Valued Senior Member
1.Do these actually exist, or are they merely a handy interpretation which seems to explain most things?

2a.Is there any way of unambiguously proving their existance, such as a photo?

2b.Would light waves be unsuitable for viewing such particles?
 
Communist Hamster said:
1.Do these actually exist, or are they merely a handy interpretation which seems to explain most things?
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You could ask this question of just about anything in physics. I suppose that, for all practical purposes, they do exist.
2a.Is there any way of unambiguously proving their existance, such as a photo?
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They seem to have no problems tracking much smaller particles in particle accelerators, though I have no idea how this is done. I think a photo is out of the question - things just get too weird at the quantum scale.
2b.Would light waves be unsuitable for viewing such particles?
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The wavelength of visible light makes it unsuitable for viewing viruses, let alone subatomic particles. Electrons make out a bit better. I think the best transmission electron microscopes around nowadays can manage a resolution of 0.6 or 0.7 Angstrom, which is enough to make out individual carbon atoms.
 
The following article I read a couple of days ago may be of interest:
The Lund group presently holds the world record for producing short laser pulses. In the High-power laser facility at the Lund University, trains of pulses where each pulse is 200 attoseconds long and separated from the next pulse by 1.3 femtoseconds, are routinely produced. A femtosecond is 10-15 seconds, i.e. one-millionth-of-a-billionth of a second, while an attosecond is still one thousand times shorter. These incredibly short light pulses allow scientists to make snapshots of the most rapidly moving constituents of atoms and molecules, the electrons.

In a paper published in this month’s issue of Nature Physics, the scientists demonstrate that attosecond pulses are an extremely powerful tool for studying the wave-like nature of electrons.
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http://www.physorg.com/news65793659.html
 
Hi Communist Hamster,

Protons and neutrons, like everything else in physics, are part of a theory used to describe the world. Most physicists, myself included, will speak about protons and neutrons as if they are real ... whatever that means. This is simply because the proton and neutron are part of a theory that is wildly successful at describing Nature. Now that the dull disclaimer is out of the way, on to the cool experiments.

It was Rutherford who first discovered that the positive charge in atoms must be concentrated in a tiny core. This was the first direct evidence for protons. We've come a long ways since that time. You can't photograph protons and neutrons because the wavelength of visible light is too long. The size of protons and neutrons is about 10^-15 meters, but the wavelength of visible light (green) is around .5 x 10^-6 meters. This is same reason why you can't feel the surface asperities (roughness on the atomic scale) of a smooth table when you run your hand across it. However, we can "see" protons and neutrons in other ways. One of the most powerful methods is known as deep inelastic scattering. Here you use very high energy electrons, rather than photons, to look at protons. This is where a lot of the evidence that protons are made up of other things (quarks and gluons) comes from. In addition, you can measure properties of the proton like its charge radius which is roughly how big of a space the charge of a proton occupies. The best number these days is something like .8750 x 10^-15 m with an uncertainty of .0068 x 10^-15 m.

Fascinating stuff really.
 
That's better discussed in the "meta-physics" forum.

I would say something exists if it has either a) volume, or b) energy (whatever form). Or both.
 
>> I would say something exists if it has either a) volume, or b) energy (whatever form). Or both.

Interesting. By those requirements protons and neutrons exist unambiguously - each has volume and energy.

However by those same criteria a magnetic field exists (it has volume and energy), and I can't think of a useful sense in which a magnetic field might be said to exist.

Also consider that both your measures - 3-distance (volume) and energy - are observer dependent. Theoretically then observers in different reference frames might disagree over whether something exists or not.
 
Well, the magnetic field does have volume, and energy.. but that is very misleading because the field itself is not the fundamental component of electromagnetic radiation.

Photons are the exchange particle, and we know they have no mass, but they do have energy. Electromagnetism exists?!
 
Hurricane Angel said:
Well, the magnetic field does have volume, and energy.. but that is very misleading because the field itself is not the fundamental component of electromagnetic radiation.

Photons are the exchange particle, and we know they have no mass, but they do have energy. Electromagnetism exists?!
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Both classical electrodynamics (including the e/m field) and quantum electrodynamics (including the exchange boson) are models. Their relative merit is in the accuracy of the predictions they make, not in their approximation to some "ultimate reality" (whatever that might be). IMO neither is more real than the other.
 
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