I don't understand this about e = mc2

[Mancunian2]

if e = mc^2
and light has no mass,
does it mean light have no energy?

 

[Apparatus]

According to measurements of pulsing stars scattered throughout the Milky Way and mystery radio signals from other galaxies, a particle of light – called a photon – can be no heavier than 9.52 × 10-46 kilograms.

https://www.sciencealert.com/how-heavy-can-a-particle-of-light-be-scientists-just-figured-it-out

 

[CrucifyMyLove]

Nvm... u r not Einstein

 

[Geminiboy]

Wave or particle? Or both?

 

[treeskull]

Light is always moving

 

[nyvrem]

light carries energy via frequency and wave iirc

 

[0nePunchm@n]

if e = mc^2
and light has no mass,
does it mean light have no energy?

is similar working scientific principle that energy cannot be created or destroyed—only transformed (the Law of Conservation of Energy)

 

[EDMW-Hates-Me]

That formula is for rest energy. Light is never at rest. Need to use the energy momentum formula.

 

[tatsit]

Come on la.. If it's useless for your daily life, why bother about it?

 

[jeffprobst]

 

[Can Or Not]

Not difficult in basic understanding.
Energy = mass x square of speed of light…

How this formula is derived, simple, first you take the formula then you derive it for 20 mins then you get the formula

 

[alex22]

Epstein = Mc2 LLP

 

[mynickname]

All of lights energy is used to move through space time?

 

[cosmothecat]

if e = mc^2
and light has no mass,
does it mean light have no energy?

No. Light definitely has energy even though it has no (rest) mass.[7][9]

### Why \(E = mc^2\) seems to cause confusion

The famous formula \(E = mc^2\) is a **special** case: it gives the energy an object has just by existing, when it is at rest.[7]
Light is never at rest and has zero rest mass, so you are trying to use a “rest energy” formula on something that has no rest mass and never sits still.

### The more general energy formula

The full special relativity relation is
\[
E^2 = p^2 c^2 + m^2 c^4
\]
where \(E\) is energy, \(p\) is momentum, \(m\) is rest mass, and \(c\) is the speed of light.[7]

- For an object at rest: \(p = 0\), so this reduces to \(E = mc^2\).[7]
- For a massless particle like a photon: \(m = 0\), so it becomes
\[
E^2 = p^2 c^2 \Rightarrow E = pc.
\]
So light has energy because it has momentum, not because it has mass.[9][7]

### How we usually write light’s energy

For a photon (a particle of light), its energy is also given by
\[
E = h\nu = \frac{hc}{\lambda},
\]
where \(h\) is Planck’s constant, \(\nu\) is frequency, and \(\lambda\) is wavelength.[4][7]
Higher frequency (like blue or ultraviolet light) means more energy per photon; lower frequency (like red or infrared) means less.

### Why we know light carries energy

- Sunlight can warm your skin and the Earth, which only makes sense if it carries energy.[7]
- Light can push on objects (radiation pressure), which shows it carries momentum and energy despite having no mass.[5][9]

So: light has no rest mass, but it still has energy and momentum, and you must use the general relativity formula (or \(E = h\nu\)), not just \(E = mc^2\), to describe it.[9][7]

 

[Ethan_]

Wave or particle? Or both?

Anything goes. Depend on the observer.