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Author Topic: Are photons destructive?  (Read 2981 times)

Offline jeffreyH

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Are photons destructive?
« on: 07/02/2014 06:00:10 »
If we accelerate particles to near light speed in the LHC and collide them then all hell breaks loose and particles fly off in all directions. This being the case why do photons, travelling at light speed, not shatter the mass they collide with?
« Last Edit: 07/02/2014 09:02:57 by chris »


 

Offline CliffordK

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Re: Why aren't photons destructive
« Reply #1 on: 07/02/2014 07:57:20 »
Photons, of course, have essentially no mass, so no kinetic energy.  A photon's energy, of course is inversely proportional to the wavelength.  Gamma rays are the highest energy photons and are moderately destructive.

I'm not sure that ultra-high-energy gamma rays can be produced in a laboratory, but perhaps we're lucky there isn't a strong source of them nearby.
 

Offline evan_au

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Re: Why aren't photons destructive
« Reply #2 on: 07/02/2014 08:58:09 »
In a sense, photons can shatter an atom - or at least, split it into two pieces.
  • An ultraviolet photon has enough energy to totally eject an outer electron from an atom.
  • An X-Ray photon has enough energy to totally eject an inner electron from an atom.
  • An extreme gamma-ray photon could in theory eject a proton from an atom - but I imagine that the probability of it hitting a proton is much less than the probability of it losing energy in multiple collisions with electrons.
 

Offline jeffreyH

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Re: Are photons destructive?
« Reply #3 on: 07/02/2014 10:26:32 »
Thanks for the replies. That makes things a lot clearer.
 

Offline alancalverd

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Re: Are photons destructive?
« Reply #4 on: 07/02/2014 11:00:26 »
And just to add to the fun, when a photon of > 1.022 MeV interacts with the electric field of a nucleus it can generate an electron/positron pair. This is an everyday example of E <=> mc^2: the e-p pair annihilates to emit two photons at 511 keV which are easly detectable.
 

Offline JP

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Re: Are photons destructive?
« Reply #5 on: 07/02/2014 13:20:12 »
In a sense, photons can shatter an atom - or at least, split it into two pieces.
  • An ultraviolet photon has enough energy to totally eject an outer electron from an atom.
  • An X-Ray photon has enough energy to totally eject an inner electron from an atom.
  • An extreme gamma-ray photon could in theory eject a proton from an atom - but I imagine that the probability of it hitting a proton is much less than the probability of it losing energy in multiple collisions with electrons.

This is why you want to put on sunscreen if you go out in the sun for too long.  The UV photons from the sun can damage the DNA in your skin which could eventually lead to cancer.
 

Offline lightarrow

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Re: Are photons destructive?
« Reply #6 on: 07/02/2014 17:26:23 »
If we accelerate particles to near light speed in the LHC and collide them then all hell breaks loose and particles fly off in all directions. This being the case why do photons, travelling at light speed, not shatter the mass they collide with?
Good question. I think the answer is that we are not able to generate photons of the same TeV energies of adrons there.
 

Offline lightarrow

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Re: Are photons destructive?
« Reply #7 on: 07/02/2014 17:30:50 »
Photons, of course, have essentially no mass, so no kinetic energy. 
On the contrary. Since they don't have mass, all their energy is kinetic.
Quote
A photon's energy, of course is inversely proportional to the wavelength.  Gamma rays are the highest energy photons and are moderately destructive.
I'm not sure that ultra-high-energy gamma rays can be produced in a laboratory, but perhaps we're lucky there isn't a strong source of them nearby.
Yes, I think this is the point: we are able to accelerate charged particles, not neutral ones, so we can't produce so high energy photons in a laboratory. Very energetic photons can be found in cosmic rays and in that case they do generate cascades of particles when they hit atoms/particles of the atmosphere.
 

Offline CliffordK

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Re: Are photons destructive?
« Reply #8 on: 09/02/2014 10:33:26 »
In a sense, photons can shatter an atom - or at least, split it into two pieces.
  • An ultraviolet photon has enough energy to totally eject an outer electron from an atom.
This is why you want to put on sunscreen if you go out in the sun for too long.  The UV photons from the sun can damage the DNA in your skin which could eventually lead to cancer.

Isn't the problem with DNA that the UV is able to break bonds in the DNA.  It isn't that one is changing Nitrogen atoms into Carbon atoms, although perhaps the loss of an electron will momentarily change the chemical properties of the atom.
 

Offline JP

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Re: Are photons destructive?
« Reply #9 on: 09/02/2014 14:14:33 »
In a sense, photons can shatter an atom - or at least, split it into two pieces.
  • An ultraviolet photon has enough energy to totally eject an outer electron from an atom.
This is why you want to put on sunscreen if you go out in the sun for too long.  The UV photons from the sun can damage the DNA in your skin which could eventually lead to cancer.

Isn't the problem with DNA that the UV is able to break bonds in the DNA.  It isn't that one is changing Nitrogen atoms into Carbon atoms, although perhaps the loss of an electron will momentarily change the chemical properties of the atom.

I meant the second of his points--ionizing radiation ejects electrons from atoms (or molecules) and this changes the chemical properties of the atom/molecule (ionizing it) which ends up damaging DNA. 
 

Offline Ian Scott ZL4NJ

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Re: Are photons destructive?
« Reply #10 on: 11/02/2014 18:56:31 »
I remember reading about the "Compton effect" where photons from galaxy clusters collide with the sparse hydrogen atoms in space and knock their electrons off through ionization. These electrons then absorb some energy from those jettisoned photons, reducing each photon's energy and therefore their wavelength. The author proposed this mechanism as an alternative to "red shift" usually attributed to Doppler shift. If correct, then light from galaxies further away would experience greater cumulative degrees of red shift, much the same as if they were traveling faster away from us, as in the expanding universe model. Consequently, the author supported a "static, steady state" model of the universe rather than an expanding one.

I am a bit vague on the author's add on suggestion that very low frequency radio signals from space supported this theory and dismisses the microwave background radiation measurements used to support the big bang model. Which model is best suited to describe current observations? Is this steady state model proposal contradicted by other evidence that only the expanding universe model can explain. Unless contradictions exist, should both theories remain in our minds.

Anyway, on the original question, photons are definitely destruction. For example, microwave ovens spin water molecules using radio waves around 2.5 GHz to heat food and apparently in the process, some authors claim denaturing various molecules. According to De Bloglie, particles have a dual particle-wave description that applies equally to microscopic objects as well as those much bigger! RF photons, using this relationship, share the same dual personality as light photons, x-rays, gamma waves and so on. However, being destructive at a sub particular level is probably another matter - this may best reside in machines like the Large Hadron Collider (LHC) although the counter-rotating particles accelerated inside should also accept an equivalent wave based interpretation. :)     
« Last Edit: 11/02/2014 18:59:09 by Ian Scott ZL4NJ »
 

Offline lightarrow

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Re: Are photons destructive?
« Reply #11 on: 12/02/2014 13:17:02 »
I remember reading about the "Compton effect" where photons from galaxy clusters collide with the sparse hydrogen atoms in space and knock their electrons off through ionization. These electrons then absorb some energy from those jettisoned photons, reducing each photon's energy and therefore their wavelength. The author proposed this mechanism as an alternative to "red shift" usually attributed to Doppler shift. If correct, then light from galaxies further away would experience greater cumulative degrees of red shift, much the same as if they were traveling faster away from us, as in the expanding universe model. Consequently, the author supported a "static, steady state" model of the universe rather than an expanding one.
I am a bit vague on the author's add on suggestion that very low frequency radio signals from space supported this theory and dismisses the microwave background radiation measurements used to support the big bang model. Which model is best suited to describe current observations? 
Doppler red shift; the other is bull....ts.

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Re: Are photons destructive?
« Reply #11 on: 12/02/2014 13:17:02 »

 

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