Photon is massless why?

[Muhammad Owais Isaac]

If photon is really massless then how it can take up energy ? 

[MigL]

It has momentum.

[exchemist]

1 hour ago, Muhammad Owais Isaac said:

If photon is really massless then how it can take up energy ? 

Any wave carries energy. A wave is just a travelling disturbance in some medium. It takes energy to displace the medium away from its equilibrium state, and that is the energy carried by the wave. A wave can't be said to have any particular mass.

A photon is a travelling disturbance in the electric and magnetic fields. Mass does not need to come into it.

[HawkII]

Probably because a Photon is its own anti-particle

[Anirudh Dabas]

2 hours ago, Muhammad Owais Isaac said:

If photon is really massless then how it can take up energy ? 

Even though they're weightless, they still pack energy. How does that work, right? Well, their energy doesn't come from mass but from their movement and frequency. It's like they're tiny packets of energy zooming around at the speed of light. This energy is related to how fast they're vibrating, kind of like how a fast song with a higher pitch can feel more energetic than a slower one. 

The energy of a photon is directly proportional to its frequency (E = hf, where 'h' is Planck's constant and 'f' is frequency). As the frequency of a photon increases, its energy also increases. Therefore, while photons are massless, they do possess energy due to their momentum and frequency, allowing them to interact with matter and transfer their energy during various physical phenomena, such as the photoelectric effect.

This might help: Light has no mass so it also has no energy according to Einstein, but how can sunlight warm the earth without energy?

Edited November 8, 2023 by Anirudh Dabas

[swansont]

28 minutes ago, HawkII said:

Probably because a Photon is its own anti-particle

The neutral pion (which has mass) is its own antiparticle, so no, that’s not it.

[Sensei]

5 hours ago, Muhammad Owais Isaac said:

Photon is massless why?

Massless means having no rest mass, i.e. being stationary, i.e. having no rest-frame of reference.

https://en.wikipedia.org/wiki/Rest_frame

It about detection rather than the rest - photon which is stationary could not be detected as photon.

 

[MigL]

The full equation is     E = root [(Mc²)² + (pc)²]

as Swansont has pointed out numerous times past.

The first tern   Mc² applies to massive stationary objects.
The second term   pc is added when that object is moving, and p denotes the momentum.

Obviously, for light, which is always moving at c and M is zero, the momentum term is the only one applicable.

[Muhammad Owais Isaac]

10 hours ago, exchemist said:

Any wave carries energy. A wave is just a travelling disturbance in some medium. It takes energy to displace the medium away from its equilibrium state, and that is the energy carried by the wave. A wave can't be said to have any particular mass.

A photon is a travelling disturbance in the electric and magnetic fields. Mass does not need to come into it.

But a wave itself is energy and anything having energy has mass also, so how  can you define wave without associating energy with it? 

[Anirudh Dabas]

5 minutes ago, Muhammad Owais Isaac said:

But a wave itself is energy and anything having energy has mass also, so how  can you define wave without associating energy with it? 

Photons have no mass, but they do have energy. The energy of a photon is proportional to its frequency.

A wave can be defined without associating energy with it. For example, a wave can be defined as a periodic disturbance in a medium. This definition does not mention energy, but it does imply that a wave must have some form of energy in order to exist.

6 hours ago, MigL said:

The full equation is     E = root [(Mc²)² + (pc)²]

as Swansont has pointed out numerous times past.

The first tern   Mc² applies to massive stationary objects.
The second term   pc is added when that object is moving, and p denotes the momentum.

Obviously, for light, which is always moving at c and M is zero, the momentum term is the only one applicable.

as @MigL rightfully pointed out, this equation states that energy is equal to mass times the speed of light squared. This means that any object with mass must also have energy.

However, not all objects with energy have mass. For example, photons have energy but no mass. This is because photons are not objects in the traditional sense. They are packets of energy that travel through space as waves.

So, while a wave cannot be defined without associating energy with it, it is possible for an object to have energy without having mass.

[exchemist]

1 hour ago, Muhammad Owais Isaac said:

But a wave itself is energy and anything having energy has mass also, so how  can you define wave without associating energy with it? 

No, a wave is not energy. A wave is a disturbance in a medium that has energy. A wave has many properties, of which energy is just one. 

If you are perhaps thinking of E=mc² , you need to be aware that that is a special case of Einstein's more general expression relating energy to mass and momentum, which is : E² = (mc²)² +(pc)² . p in this expression is momentum.

For objects at rest relative to the observer, p=0, so it reduces to the familiar E=mc².

But for light, which has no rest mass, m=o, so the expression reduces instead to E=pc. It is this that governs the energy of a photon, not E=mc².

In fact, if you apply to this de Broglie's relation from quantum theory, which relates momentum to wavelength: p=h/λ (h is Planck's constant), you get something interesting. For any wave, the speed, c, frequency ν, and wavelength, λ, are related by c = νλ. So you can write 1/λ = ν/c. de Broglie's expression then becomes p = hν/c, and so E=pc becomes E=hν.   This is Planck's famous equation for the energy of electromagnetic radiation.   

 

[Muhammad Owais Isaac]

6 hours ago, Anirudh Dabas said:

Photons have no mass, but they do have energy. The energy of a photon is proportional to its frequency.

A wave can be defined without associating energy with it. For example, a wave can be defined as a periodic disturbance in a medium. This definition does not mention energy, but it does imply that a wave must have some form of energy in order to exist.

as @MigL rightfully pointed out, this equation states that energy is equal to mass times the speed of light squared. This means that any object with mass must also have energy.

However, not all objects with energy have mass. For example, photons have energy but no mass. This is because photons are not objects in the traditional sense. They are packets of energy that travel through space as waves.

So, while a wave cannot be defined without associating energy with it, it is possible for an object to have energy without having mass.

But dear how can you define disturbance without a medium there must be some kind of force involved in disturbing the medium can you disturb any system without force. If no the  how do physicists claim that photon has energy but not mass and its energy depends on its frequency or wave density... Do they mean energy can exist I dependent of matter or mass. If yes then everything in the universe is actually a wave that carries energy only and mass or matter is just an illusion. 

[exchemist]

2 minutes ago, Muhammad Owais Isaac said:

But dear how can you define disturbance without a medium there must be some kind of force involved in disturbing the medium can you disturb any system without force. If no the  how do physicists claim that photon has energy but not mass and its energy depends on its frequency or wave density... Do they mean energy can exist I dependent of matter or mass. If yes then everything in the universe is actually a wave that carries energy only and mass or matter is just an illusion. 

Yes, there is energy in fields, for example in an energised electromagnet. With photons, the “medium” is the electric and magnetic fields. A photon is a travelling disturbance in those fields.

[Muhammad Owais Isaac]

10 minutes ago, exchemist said:

Yes, there is energy in fields, for example in an energised electromagnet. With photons, the “medium” is the electric and magnetic fields. A photon is a travelling disturbance in those fields.

You are absolutely correct, particles are result of disturbance in field we can say the ammount of ammount of disturbance is measure of mass of particle, every field has its own respective particle resulted by disturbance in field. 

Edited November 9, 2023 by Muhammad Owais Isaac

[swansont]

33 minutes ago, Muhammad Owais Isaac said:

Do they mean energy can exist I dependent of matter or mass

Yes, there are things that are not matter and have no mass that have energy. Such as photons.

Quote

If yes then everything in the universe is actually a wave that carries energy only and mass or matter is just an illusion. 

That doesn’t follow. 

If X exists, everything is X, is faulty logic

[Muhammad Owais Isaac]

10 minutes ago, swansont said:

Yes, there are things that are not matter and have no mass that have energy. Such as photons.

That doesn’t follow. 

If X exists, everything is X, is faulty logic

It means the disturbance in photon field which produces photon is so small that photon does not qualify to carry mass, thit may sound weird but this may be a true assumption. 

[exchemist]

43 minutes ago, Muhammad Owais Isaac said:

You are absolutely correct, particles are result of disturbance in field we can say the ammount of ammount of disturbance is measure of mass of particle, every field has its own respective particle resulted by disturbance in field. 

No, you have made that bit up about the amount of disturbance being associated with mass. 

[joigus]

12 minutes ago, Muhammad Owais Isaac said:

It means the disturbance in photon field which produces photon is so small that photon does not qualify to carry mass, thit may sound weird but this may be a true assumption. 

Or...

It may sound weird and be a false assumption as well.

Example: Seals are grey because polar bears are white.

It sounds weird and it is false.

"Photons don't carry mass because they always entail a very small disturbance of the vacuum" is as false a statement as can be.

X rays are an example. Extremely-high-energy photons are as massless as extremely-low-energy photons.

x-posted with @exchemist, who said more or less what I said.

[swansont]

1 hour ago, Muhammad Owais Isaac said:

It means the disturbance in photon field which produces photon is so small that photon does not qualify to carry mass, thit may sound weird but this may be a true assumption. 

How would you test this? We can have EM radiation produce a pretty strong field.

[studiot]

22 hours ago, Muhammad Owais Isaac said:

If photon is really massless then how it can take up energy ? 

Here are two pages from the book by Nobel Physicist Frank Wilczek that may help you.

Fundamentals  Ten Keys to Reality.

 

His whole theme is to cut down modern Physics, including the maths, to the bare bone essentials, so you might finds lots of useful understandable explanations here.

 

Note here he says that none one really knows why particles have the mass they do and he lists at least three zero mass particles.

 

In the main text he lists mass as on of the three essential characteristics or properties of matter.

You will have to read the book to learn what he says about energy.

You might be surprised

[mistermack]

17 hours ago, Sensei said:

Massless means having no rest mass, i.e. being stationary, i.e. having no rest-frame of reference.

https://en.wikipedia.org/wiki/Rest_frame

It about detection rather than the rest - photon which is stationary could not be detected as photon.

That's what I thought. A photon isn't a photon, if it was at rest. And if a particle that has mass could be accelerated to the speed of light, it would have infinite kinetic energy. 

The nearest thing I've heard of, of a photon at rest, is the theoretical case where the photon is trapped between two perfect mirrors, endlessly reflecting back and forth. In that case, the overall system gains mass, equivalent to the energy of the photon. So you can have mass, or a photon, but you can't have a photon with mass. 

[swansont]

4 hours ago, mistermack said:

The nearest thing I've heard of, of a photon at rest, is the theoretical case where the photon is trapped between two perfect mirrors,

The photon is not at rest. There is a standing wave in the classical picture. but the photon is bouncing back and forth.

There is no rest frame for a photon - no way to transform between an arbitrary frame and this proposed rest frame and back.

[mistermack]

2 hours ago, swansont said:

The photon is not at rest. There is a standing wave in the classical picture. but the photon is bouncing back and forth.

There is no rest frame for a photon - no way to transform between an arbitrary frame and this proposed rest frame and back

No, the photon doesn't have a rest frame. But the system as a whole does. And it's the system as a whole that has an increase in mass equivalent to the energy of the photon. And of course, if the system captures the photon, then the system as a whole gains the momentum that the photon would have, if it wasn't captured.

 

6 hours ago, studiot said:

Note here he says that none one really knows why particles have the mass they do and he lists at least three zero mass particles.

I personally view particles with mass as being similar to the theoretical photon between mirrors that I posted about above, where the photon is constrained and produces an increase in effective mass of the system as a whole. I think of massive particles as massless particles that would normally be travelling in a straight line at c, that are somehow self-constrained, orbiting a centre, instead of straight-lining at c. If that were to happen, then the overall system would gain mass, like the mirror system. 

[martillo]

On 11/8/2023 at 4:29 PM, Muhammad Owais Isaac said:

If photon is really massless then how it can take up energy ? 

Really a good question.

In Physics by definition something has momentum p if it has mass and velocity and the momentum is defined as p = mv.

A massless thing (m = 0) would have then by definition zero momentum p = 0 and it also would have zero energy E = 0.

I agree with the OP that there could be a real problem in the subject.

 

Considering the "wave-particle duality", the wave-like behavior of a photon gives a frequency f and an a wave-length λ = c/f to it.

The Planck-Einstein energy formula for a photon gives an energy E = hf to it and we can deduce: E = hc/λ.

Now, considering that the velocity of a photon is c, the De Broglie law would give λ = h/mc for a photon and so we would obtain a mass for a photon satisfying hf = mc². A photon would have a finite mass m = hf/c².

 

The problem is with Relativity Theory. In Relativity Theory photons must be massless but there is that problem with the definitions of momentum and energy...

 

Edited November 11, 2023 by martillo

[exchemist]

2 hours ago, martillo said:

Really a good question.

In Physics by definition something has momentum p if it has mass and velocity and the momentum is defined as p = mv.

A massless thing (m = 0) would have then by definition zero momentum p = 0 and it also would have zero energy E = 0.

I agree with the OP that there could be a real problem in the subject.

 

Considering the "wave-particle duality", the wave-like behavior of a photon gives a frequency f and an a wave-length λ = c/f to it.

The Planck-Einstein energy formula for a photon gives an energy E = hf to it and we can deduce: E = hc/λ.

Now, considering that the velocity of a photon is c, the De Broglie law would give λ = h/mc for a photon and so we would obtain a mass for a photon satisfying hf = mc². A photon would have a finite mass m = hf/c².

 

The problem is with Relativity Theory. In Relativity Theory photons must be massless but there is that problem with the definitions of momentum and energy...

 

Your "definition" of momentum is wrong and you are using the wrong formula. According to special relativity, E=mc² is not applicable to a photon. I went over this in post 11 of this thread.