I hear a lot of people saying that neutrino is the lightest subatomic particle but according to me a photon must be the lightest as nothing can travel faster than light because it gets heavier and heavier and bends time.

  • 5
    $\begingroup$ If you are thinking of the PHOTON as the particle of light, then yes, it is massless (the proton is far heavier than the neutrino and the photon). But it is not a matter particle, it is a force carrier, so people don't usually include this in "subatomic particles". $\endgroup$
    – ACuriousMind
    Jun 17, 2014 at 16:59
  • 2
    $\begingroup$ The upper bound on the mass of electron neutrino is around 2 eV. The upper bound on the mass of the photon is about $10^{-17}$ eV. To the best of our current ability, photons appear to be lighter than some neutrinos. $\endgroup$
    – Kyle Kanos
    Jun 17, 2014 at 17:06
  • $\begingroup$ The above two comments are the best answer so far! $\endgroup$
    – innisfree
    Nov 23, 2015 at 11:59
  • $\begingroup$ Photon is the first particle of light that we can observe through our equipment. Before photons, there are much faster particles that consist of each other. However, these particles cannot be observed through mechanical equipment because the equipment itself is made of those particles. We, being made of those particles, can access this field of information only through consciousness, as thoughts are lighter and faster than matter. $\endgroup$
    – Rus
    Sep 4 at 1:24
  • $\begingroup$ This is where science and mysticism intersect. Science should be involved, but sometimes it is too resistant to start studying and learning. A skewed worldview leads to a distorted picture, creating an unnecessary puzzle to solve. $\endgroup$
    – Rus
    Sep 4 at 1:24

3 Answers 3


There's a subtle distinction here, which is that neutrinos are matter particles (having spin $\hbar/2$ and obeying Pauli's exclusion principle) while photons are force carriers (having spin $\hbar$ and obeying Bose-Einstein statistics).

There are three flavors of neutrino and they all have different masses. Therefore at least two of them are massive; whether the lightest neutrino is massless is an open question.

Among the force-carrying particles, the photon, gluon, and (hypothetical) graviton are all identically massless.


Photons are massless particles, while neutrinos have a tiny but non-zero mass.


Light particle is a vague term actually. There are two ways I can think of a particle being "light".

  1. If you mean has least mass than photons have zero mass so it is indeed lightest. The exact mass of lightest neutrino is not yet known.
    It is actually wrong to talk about "A photon" because it is not a single particle. Photon is a "quanta" of electromagnetic waves(or light) and it not, strictly speaking, correct to call it a"particle" of light thought it has properties similar to particles.
  2. If you mean which particles does not interact with other particles then the answer is different. Even though photons have no mass but they have a momentum. So when light bounces off a surface it exerts a force. $$p=\frac{h}{\lambda}$$ It means that light with lower wavelength, $\lambda$, will have higher momentum, $p$.
    So momentum of photon depends on it's energy and can be greater than momentum of a neutrino.
  • 3
    $\begingroup$ So electrons are not particles because they are quanta of the electron field? $\endgroup$
    – jinawee
    Nov 23, 2015 at 10:46

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.