# About pair production using light

• A
wasong
TL;DR Summary
Can light make two pairs? (assuming enough energy to make two pairs)
If so, why?
Can light make two pairs? (assuming enough energy to make two pairs)
If so, why? or If not, why not?

Welcome to PF.
Two pairs of what?

• wasong
Welcome to PF.
Two pairs of what?
Thank you~ (electron+electron+positron+positron)!

Homework Helper
Gold Member
2022 Award
Thank you~ (electron+electron+positron+positron)!
Whence these pairs?

wasong
Whence these pairs?
I don't understand. What's mean "Whence"?

wasong
wasong
Whence: from what place, source or cause.

https://www.merriam-webster.com/dictionary/whence
in a book: Electromagnetic waves (with enough energy) = γe− + e+
in my opinion: Electromagnetic waves (with enough energy) = γe− + e+ that's right! or Electromagnetic waves (with enough energy) = γe− + e− + e+ + e+ also that's right! because There's no problem if you keep Conservation of energy and conservation of charge.

Gold Member
2022 Award
in a book
That is NOT a proper citation on this forum. You might as well say "some guy on a bus told me".

• wasong
That is NOT a proper citation on this forum. You might as well say "some guy on a bus told me".
Sorry.. The book is Concepts of Modern Physics. I was not good at English and citation.

• phinds
Homework Helper
Gold Member
2022 Award
in a book: Electromagnetic waves (with enough energy) = γe− + e+
in my opinion: Electromagnetic waves (with enough energy) = γe− + e+ that's right! or Electromagnetic waves (with enough energy) = γe− + e− + e+ + e+ also that's right! because There's no problem if you keep Conservation of energy and conservation of charge.
This pair production can only take place in the presence of an atom of molecule - which is required to balance momentum. I don't know why precisely only one pair may be produced - I'm sure someone will answer that - but it's not enough just to say that energy and momentum are conserved. There must be a possible interaction between the photon and the atom that produces two pairs.

Staff Emeritus
Homework Helper
in a book: Electromagnetic waves (with enough energy) = γe− + e+
in my opinion: Electromagnetic waves (with enough energy) = γe− + e+ that's right! or Electromagnetic waves (with enough energy) = γe− + e− + e+ + e+ also that's right! because There's no problem if you keep Conservation of energy and conservation of charge.
You probably mean "photon," not electromagnetic waves. Pair production is one of the basic processes in QED, and it's actually ##\gamma + \gamma \to e^- + e^+##. There are probably higher-order processes which can produce multiple electron-positron pairs from a single pair of photons, but it's much less likely to occur. And, of course, if you start with multiple pairs of photons, each could produce an electron-positron pair.

wasong
You probably mean "photon," not electromagnetic waves. Pair production is one of the basic processes in QED, and it's actually ##\gamma + \gamma \to e^- + e^+##. There are probably higher-order processes which can produce multiple electron-positron pairs from a single pair of photons, but it's much less likely to occur. And, of course, if you start with multiple pairs of photons, each could produce an electron-positron pair.
Does the word "less likely" mean that there is a possibility of it happening? from a single pair of photons

wasong
Does the word "less likely" mean that there is a possibility of it happening? from a single pair of photons
If the answer to my question is yes, where can I find the relevant concept or data?

Homework Helper
Gold Member
2022 Award
You probably mean "photon," not electromagnetic waves. Pair production is one of the basic processes in QED, and it's actually ##\gamma + \gamma \to e^- + e^+##. There are probably higher-order processes which can produce multiple electron-positron pairs from a single pair of photons, but it's much less likely to occur. And, of course, if you start with multiple pairs of photons, each could produce an electron-positron pair.
This is a different process: this is pair production from a pair of photons. It's the reverse of pair annhililation.

An electron-positron pair can annhililate and produce an even number of photons; but, I'm not sure that two photons could produce more than one electron-positron pair. I suspect that you can only get one electron-positron pair per pair of photons.

And similarly in the case of pair production from a single photon where the interaction involves additionally an atom or molecule.

Staff Emeritus