I have recently become interested in cosmic rays. This is a direct result of some ongoing discussions in various threads on this board, and more specificly because of some interesting remarks about "redshifting" and "blueshifting". If you are interested in attempting to educate a biologist on some of the finer points of this area of astrophysics please read on.

In a post from a boardmember named darkhunter in this thread: http://www.badastronomy.com/phpBB/vi...c=3560&forum=2 he/she speaks about photons shifting into cosmic rays if one was to run into them while theoretically travelling at some significant portion of c. I have also read similar statements from other posters on other threads, but I will not attempt to reference them all.

Upon hearing this suggestion that shifting could result in "apparent" cosmic rays to such an observer I got very interested. I had been under the impression that cosmic rays were known to be particles travelling at great speed (no particle/wave duality involved just really fast protons or electrons). So, this led me to the obvious conclusion that if the premise that a photon can be shifted to a cosmic ray as observed by someone travelling really fast, does this not mean that the only difference between a photon and proton is the velocity, direction, and orientation of the observer relative to the subject?

2nd question:
I was also under the impression that cosmic rays, or rather the protons/electrons involved in cosmic rays, do not actually travel at c, but rather just shy of c. In this case, if it is possible for a photon to be shifted to a cosmic ray, then has not the photon actually slowed down (but apparently conserved energy seeing how it gained mass), as measured by the observer that is seeing the shift?

Could some kind soul please clarify this against current dogma? (Please note: I am not looking for alternate cosmologies here, which is why I have chosen the general astronomy section rather than "against the mainstream"). In the likely event that a proper response would take too long, advice on a good reference would be much appreciated.

Thanks in advance,

Sheki

Not an expert here, so take my thoughts with a grain of salt.

Cosmic rays are indeed different from Gamma and X-rays. The former are accelerated subatomic particles, and the latter are part of the EM spectrum.

Photons, unlike protons and such, are unique. They are considered to have zero rest mass. This is what allows them--no, forces them, to travel at c. If they had any mass at all, they'd be unable to reach it. And for the same reasons they can't travel slower than light either. They behave according to the particle/wave duality and are subject to such things as doppler shifts.

Regular subatomic particles, OTOH, all have measurable rest masses, and are subject to relativistic motion. They can't reach c, no matter how hard they try. Their speeds can vary from very slow to very fast. The smallest of them, such as neutrinos, have such tiny masses that it's easy to accelerate them to close to c. But I think they are always considered particles. They don't exhibit doppler effects. They do, I believe, have mass and momentum effects though. Faster particles will do more damage on impact than slower ones. More massive particles will hit harder than less massive ones.

The doppler shift of light is sometimes hard to grasp. Remember that c is a constant. It cannot change in vacuum. But if the source of light is travelling towards you, you have to add the momentum to the energy of the light. Light always travels at c, so changing its speed is right out. So the energy instead gets transferred to the wavelength of the light, making it more energetic instead. The same thing happens in reverse when the source is moving away. Energy is subtracted, so the wavelength gets longer.

Another easy analogy is to think of a boat racing along the water. Let's say the waves are coming from the north at 20 per minute. If you head into the waves, you will be hitting them more often and maybe going through 40 per minute.. If you race along with the waves, you will hit less of them and may only be hitting 10 per minute. But the overall speed of the waves hasn't changed.

Hope this helps. [img]/phpBB/images/smiles/icon_smile.gif[/img]

__________________
...And that, my liege, is how we know the Earth to be banana-shaped. --Sir Bedevere

David,

Thanks for the reply, but I think all you have done is add some background information for my original question. I am quite comfortable with the concept of doppler shift, the increase/decrease in wavelength/frequency associated with it, and I understand that c is supposed to be c regardless of the reference frame of the observer. You have quite aptly summed up my base assumptions prior to asking the first question.

So, are you effectively disagreeing that EM can be shifted to a cosmic ray? Or have I misunderstood your response?

Sheki

Sorry, I wasn't sure exactly how much you understood, so I was trying to be thorough.

Yes, I am disagreeing. The EM spectrum is photons, and nothing but. Only photons can exhibit doppler shift because only photons are light, and only photons travel at c.

Cosmic rays are particles, protons, electrons and such, and they all have mass. As such they can never reach c, and can never experience the EM doppler shift. They can gain relativistic mass and become more energetic, but there's no spectrum to shift. They're just particles.

This is my understanding at least. More egghead types can correct me on my mistakes.

But this has led me to a new thought of my own. Is it only photons that exhibit the particle/wave duality, or does it apply in other areas as well?

__________________
...And that, my liege, is how we know the Earth to be banana-shaped. --Sir Bedevere

David,

quote//
"But this has led me to a new thought of my own. Is it only photons that exhibit the particle/wave duality, or does it apply in other areas as well?"
//end quote

That is where I was going with this as well. [img]/phpBB/images/smiles/icon_smile.gif[/img]

I had hoped it would be a simple answer "ie. no, EM cannot be shifted to cosmic rays - end of story". I guess we will both just have to wait until a specialist provides some additional illumination.

hmmmmm "additional illumination" I wonder if that counts as a pun, given the context...

Sheki

Electrons have been observed to exhibit wave properties. Protons have a much higher mass and do not exhibit wave properties as much, but it is definitely possible.

I think the reason you don't hear about the red shift of cosmic rays is that problem of measuement. We measure red shift of the spectrum of an object by looking at how far certain emission and absorption lines have moved from their rest frame values. You can't do this with protons! You would need to know their initial energy to do the calculation, and we have no way of knowing that. We can only measure them when they arrive here.

Rob

What would be cosmic rays when moving at close to light speed would be any "dust" on your course.

From your "high speed" frame of reference, these dust particles and even single atoms will be coming at you from one direction with a great deal of engery, much like cosmic rays from a "stationary" reference point (such as on Earth)

edit: No, as far as I know EM cannot turn into cosmic rays (but I am mostly self taught [img]/phpBB/images/smiles/icon_smile.gif[/img] )
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Words define reality, but they can't alter it.

<font size=-1>[ This Message was edited by: darkhunter on 2003-01-21 15:40 ]</font>

"cosmic ray" is a term like "germ". It's a class of phenomenon that contains several different members. Extremely high energy gamma rays (like 10²⁰ eV or so) are sometimes referred to as cosmic rays. No, they don't switch over into particles and slow down. What can happen, for photons of greater than 1 MeV, is that they can spontaneously split into electron-positron pairs. Energy and all the other usual conserved quantities are still conserved.

Don

I disagree
protons , electrons are particles, traveling as a WAVE ( QM's duality particle/wave ) and as a wave it should show redshift ( Doppler).

Because they have rest mass, they can't ever reach c. With regard to Doppler shift, it's an interesting point. First, you must consider the equation:

deltalambda/lambda = v/c

Remember, v/c cannot be greater than 1. Therefore, deltalambda/lambda can't either. Since, with de Broglie waves, lamda is so small, (for a proton travelling at a tenth the speed of light, lambda is 1.3×10^-14, which if we were shrunk down to the size of a nucleus, that would be about the size of the atoms of our nanoscopic bodies), delta lambda must be even smaller. That's a very, very, very, very, very, ×10^pi small.

But, there is also an issue of applicability. The general equation to describe waves, v=f×lambda, doesn't work for de Broglie waves, so I'm not sure if the Doppler Equation would work either.

DoctorDon said:

" "cosmic ray" is a term like "germ". It's a class of phenomenon that contains several different members. Extremely high energy gamma rays (like 1020 eV or so) are sometimes referred to as cosmic rays. No, they don't switch over into particles and slow down. What can happen, for photons of greater than 1 MeV, is that they can spontaneously split into electron-positron pairs. Energy and all the other usual conserved quantities are still conserved."

Reply:
Thanks, that clarifies things greatly. However, that bit about a photon "splitting" into two particles is pretty amazing. All sorts of questions spring to mind:

Does the electron-positron pair continue travelling at c?

Is the pair bound to each other, or can they go flying off on their own?

If they are bound then what keeps them from mutually annihilating each other?

Or is the "electron-positron pair" just a shorthand way of stating "a photon with the equivalent energy of an electron-positron annihilation"?

Also, if an electron-positron pair is produced, then that pair effectivly constitutes a "particle" (actually two particles). In this instance it would appear that it is possible to create a "particle" cosmic ray through redshift. N'est pas?

Upon further consideration, I take it back. This has not clarified things at all. But it has furthered my understanding considerably. Thanks.

Sheki

Yeah, after reading all this, I guess I can say I am confused on a deeper level [img]/phpBB/images/smiles/icon_smile.gif[/img]

Rob

I'm not an expert, but wouldn't this only happen when they "interact" with the "high speed" observer?

__________________
"Light thinks it travels faster than anything but it is wrong. No matter how fast light travels it finds the darkness has always got there first, and is waiting for it." — Terry Pratchett, Reaper Man

441!!!! :)

David Hall,
Perhaps you want to adjust your statement above to reflect your error in the statement:

Quote"Only photons can exhibit doppler shift..."

Surely you recall the doppler shift exhibited by railroad train whistles?

As to the original question. Cosmic rays are helium nuclei (two protons and two neutrons), which when moving at moderately high speeds are called alpha particles and when moving nearly the speed of light are called cosmic rays because they exhibit quantum particle/wave dualities. And if a helium nucleus moving at nearly the speed of light (a cosmic ray) collides with a stationary helium nucleus the resultant products are the same as two cosmic rays colliding. In effect the stationary helium nucleus reacts as if it has been impacted by a cosmic ray and the moving helium nuclei reacts as if it also has been impacted by a cosmic ray.





<font size=-1>[ This Message was edited by: SAMU on 2003-01-22 13:24 ]</font>

consider electrons coming to earth with different wavelenghts. we expect a redshift -- or should I say a rightshift -- of the spectrum.

can we see this spectrum in an experiment ?