107 views

### Can there be an acceleration when no net force acts on a massless object?

If no net force acts on a massless object can there be any acceleration of the object? My attempt: $$F=ma\\ \implies a=F/m\\ \implies a=0/0$$ $\implies a$ can be anything.
6k views

### If a 1kg mass was accelerated close to the speed of light would it turn into a black hole?

I'm a big fan of the podcast Astronomy Cast and a while back I was listening to a Q&A episode they did. A listener sent in a question that I found fascinating and have been wondering about ever ...
760 views

### Why does light not slow down?

Clearly light bounces off of things, going really really fast. I'm curious to understand how light interacts with matter in order to bounce without: Applying force to the object Losing speed So my ...
39 views

### How is speed of light constant if it bends? [duplicate]

Gravitational lensing causes light to be bent.If light changes direction how can it be travelling with constant speed?Where am I wrong.Thanks for any help.
65 views

### how photon gets accelerated instantaneously to speed of light? [duplicate]

i understand that the photon when emitted is already travelling in the speed of light but how can it go from 0 to speed of light instantaneously. is it because photon is a mass less particle and the ...
83 views

### Can photons accelerate? [duplicate]

I was just wondering if there's a (hypothetical) situation where a photon could accelerate and what the consequences of this might be?
62 views

### Does light ever experiences acceleration? [duplicate]

Till now I have learned that light has fastest speed. But I have also noticed that wherever it travels it only experiences retardation. So I wanted to know if light ever felt acceleration naturally in ...
18 views

### When light changes medium, does it decelerate, or instantaneously change speed? [duplicate]

The velocity of light changes between mediums, but does light specifically decelerate when it enters a denser medium, or is the change is speed instantaneous?
9k views

### Why can't photons have a mass?

Why can't photons have a mass? Could you explain this to me in a short and mathematical way?
160 views

### Do Photons Accelerate Upon Creation? [duplicate]

Of course the speed of light is constant relative to everything. Its frequency can change, but its speed is constant. Photons may be absorbed by atoms or release by atoms as energy, but as soon as it ...
102k views

### If photons have no mass, how can they have momentum?

As an explanation of why a large gravitational field (such as a black hole) can bend light, I have heard that light has momentum. This is given as a solution to the problem of only massive objects ...
39 views

### Is there any acceleration of light? [duplicate]

I find it hard to believe that photons always travel with 3 x 10^8 m/s just from the start. But there must be some acceleration of light. Maybe huge or taking place in picoseconds. So what maybe the ...
159 views

### At Interfaces Does Light Have to Accelerate?

First, I'm not sure if photons have to "get up to" the speed of light, or if they are thrown into existence at that speed. I know that they should just be generated moving at their speed, and I know ...