# Linked Questions

3answers
9k views

### Could any object have zero mass? [duplicate]

Energy and mass are interrelated. As everything has energy could any object be massless? For example a photon is a packet of energy but still it is considered to be a massless particle. Why is it so?
3answers
15k views

### Is a photon really massless? [duplicate]

If a photon travels at a speed of light and its massless then it must have no energy but this is not the case as we see in photo electric effect. Also help me to know what are photons made of, how are ...
2answers
2k views

### Do photons have mass? [duplicate]

As a student in a highschool physics class, my teacher has repeatedly told me that photons are massless. Yet, I have also heard from other sources that photons have momentum. If photons were to have ...
2answers
6k views

### What is the mass of a photon moving at the speed of light? [duplicate]

What is the mass of a photon moving at the speed of light? And if it does not have mass, how is it affected by gravity? Also why does Einstein's general relativity support that a gravitational wave ...
1answer
7k views

### Do Waves have mass? [duplicate]

Do any form of electromagnetic waves like visible light have mass? It is known that all electromagnetic waves have energy. According to Einstein's $$E^2=p^2c^2 + m^2c^4$$ formula, the energy of a ...
2answers
1k views

### Photons have no mass. So, why does $E = pc$ hold? [duplicate]

It's a somewhat theoretical question. In special relativity, The energy of a photon is given by $E = pc$. But, my argument is that, since photons have no mass, how can they have a momentum $p$? The ...
1answer
1k views

### Why are two photons created in annihilation? [duplicate]

My textbook says it is because momentum has to be conserved but I don't see how photons can have momentum since they have zero mass (according to my book).
1answer
230 views

### How to get the accurate relativistic momentum form for photons? [duplicate]

I have studied from Griffiths, the relativistic form of momentum is $$p = \frac{1}{\sqrt{1-\frac{v^2}{c^2}}} m_0v$$ Now when I evaluate the momentum for photon, I just insert $v=c$ and $m_0=0$ and I ...
1answer
518 views

### Why does a photon have momentum and no mass, yet $p=mv$? [duplicate]

Okay so according to my high-school knowledge I know about inertia and momentum. Now I have a question regarding the photon which my teachers say that is to be learnt in higher classes(and thus not ...
0answers
482 views

### If photons don't have mass, how can they accelerate objects? [duplicate]

As far as I know photons don't have mass but they do have momentum ($p=mv$). Scientists say that if we put a shiny (reflective) shield of large radius in the vacuum of space, then light from sun will ...
1answer
146 views

### Why would a photon striking an electron “make both recoil”? [duplicate]

Why would a photon striking an electron "make both recoil" as I read in an answer to another question. If the photon is massless, how can it make an electron change momentum?
1answer
285 views

### Do photons have no mass? [duplicate]

My Quantum Mechanics' teacher said today on the class that photons don't have mass. I was puzzled because I knew that photons have momentum. If a particle hasn't mass then its momentum sould be $0$ ...
1answer
170 views

### If photons have no acceleration, how can they have energy and momentum? [duplicate]

The change in speed of a photon with respect to time is 0 as photons travel at $c$ forever. If no change in speed exists, how can photons have momentum and acceleration? I guess they don't work like ...
1answer
108 views

### How does Light have momentum without mass? [duplicate]

My question is regarding gravity in black holes. It is said that light can’t escape the enormous gravitational force in black holes; however, is it not true that gravity is directly proportional to ...
2answers
119 views

### Why does photon emit a frequency when its rest mass is zero? [duplicate]

This one really boggles my mind. In the equation $E=mc^2$ and $E=hv$, we can equate $hv=mc^2$. Then, $v/m=c^2/h=k$ (constant) Therefore, $v=k.m$ So, $v$ is directly proportional to m. Lets see the ...

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