How can particles have no mass

This is a fundamental property of our space and an experimental fact. Even elementary particles and radiation can't afford violating this principle. But if momentum is conserved, the forces between any two isolated particles locked in an orbit must be of the inverse square type as given in Bertrand theorem. Actually the theorem allows a spring type force Hook's spring force too, but this can be shown to be a limiting case of the inverse square force.

Thus Newton's law of gravity and Coulomb's law of static interactions emerge as radiation condenses into matter. Now, the formula for the bending of a projectile in the vicinity of a massive object in the Newton's theory the inverse square force theory have only the speed of the projectile in it, and not its mass. The mass simply cancel's out. According to this fact, Newton proceeded to calculate the deflection of light caused by the sun for example. As it happened, Einstein calculated the same angle and found it to be double that of Newton.

People without deeper thinking announced that this meant that Newton's formula is wrong and the whole theory should therefore be discarded- despite the fact that the mass of the sun is not that of a black hole to merit a big modification of the Newton's theory. The rays that are drawn straight from the source to the sun surface can't cross to the other side- they hit the Sun's surface instead.

What we see is rays that come from an angle equal to that after crossing the Sun's surface. The two results support each other in a sense. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams?

Learn more. If photons have no mass, how can they have momentum? Ask Question. Asked 10 years, 10 months ago. Active 6 months ago. Viewed k times. How can photons have momentum?

How is this momentum defined equations? Improve this question. Add a comment. Active Oldest Votes. Improve this answer. Sometimes people ask "If light has no mass how can it be deflected by the gravity of a star? One answer is that all particles, including photons, move along geodesics in general relativity and the path they follow is independent of their mass.

The deflection of starlight by the sun was first measured by Arthur Eddington in The result was consistent with the predictions of general relativity and inconsistent with the newtonian theory.

Another answer is that the light has energy and momentum which couples to gravity. The energy-momentum 4-vector of a particle, rather than its mass, is the gravitational analogue of electric charge.

The corresponding analogue of electric current is the energy-momentum stress tensor which appears in the gravitational field equations of general relativity.

The energy and momentum of light also generates curvature of spacetime, so general relativity predicts that light will attract objects gravitationally. This effect is far too weak to have yet been measured. The gravitational effect of photons does not have any cosmological effects either except perhaps in the first instant after the Big Bang.

And there seem to be far too few with too little energy to make any noticeable contribution to dark matter. For an alternative viewpoint of relativistic mass, see the article by T. And now the team at Princeton has shown that they do indeed exist. In fact, they've shown that in a test medium, Weyl electrons can carry charge at least 1, times faster than electrons in ordinary semiconductors, and twice as fast as inside wonder-material graphene.

They're also far more efficient than electrons, the team reports in Science , because the particle's spin is both in the same direction as its motion which physicists call 'right-handed and opposite its direction 'left-handed' at the same time.

This means that all the fermions move in exactly the same way and can traverse through and around obstacles that scatter normal electrons. These are very fast electrons that behave like unidirectional light beams and can be used for new types of quantum computing. In summary, all objects with no mass can never be at rest and must travel at speed c in all reference frames. Light is such an object, and the universal speed limit c is named the speed of light in its honor.

But light is not the only massless object. Gluons and the hypothetical gravitons are also massless, and therefore travel at speed c in all frames. How can an object have momentum without mass? It can do this if it is a wave. A wave transports momentum via its waving motion and not by physically transporting an object with mass. An object with high momentum such as a truck can greatly influence the object it collides with such as a barrel.