Exploring the Physics of Light: Does it Have Mass?

In summary, the question is asking if light has mass, and the answer is yes. However, only when light is traveling close to the speed of light does this mass become significant. It seems that light creates its own energy when traveling at the speed of light. However, there are still some flaws in this explanation, and the FAQ in this section of the website can help better understand the concept.
  • #1
Foxcroft
6
0
Hello, back again.

I have another question that I have been pondering about.

The question I don't get is: light has mass yeah?? even if it's a really small amount. But then how does light go as fast as the speed of light?? Because you would need infinite energy to get at that speed, carrying that mass a long time/distance at that speed surely must use a lot of energy.

But then I thought if E=mc2 then entergy is mass x speed of light2 so doesn't that mean, that if it's traveling at the speed of light, it creates it's own energy? That's the only explanation I could come up with.

What flaws do I have, as I'm sure I've got some.

Thanks Jack.
 
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  • #2
Energy has mass, but it's only when it's traveling close to the speed of light that this mass becomes significant.

Think of this way, if no object can reach c then how does it slow down in a vacuum if it experienced a constant acceleration, the only way to decrease the acceleration is to increase the mass.

In the case of light itself, well it's light nothing can travel faster than it, and it contains a tremendous amount of energy (afterall it IS a form of energy); light from the stars travels millions of light years yet it still can do work on the electrons within the human eye.
 
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  • #3
When you say "mass" do you mean "relativistic mass" (mr) or "invariant mass" (m0)? These two meanings are not the same. The invariant mass of a particle is independent of its speed v, whereas relativistic mass increases with speed and tends to infinity as the speed approaches that of light, c.

This can be stated mathematically as,

mr = E/c^2

m0 = sqrt(E^2/c^4 - p^2/c^2)
 
  • #4
Foxcroft said:
Hello, back again.

I have another question that I have been pondering about.

The question I don't get is: light has mass yeah?? even if it's a really small amount. But then how does light go as fast as the speed of light?? Because you would need infinite energy to get at that speed, carrying that mass a long time/distance at that speed surely must use a lot of energy.

But then I thought if E=mc2 then entergy is mass x speed of light2 so doesn't that mean, that if it's traveling at the speed of light, it creates it's own energy? That's the only explanation I could come up with.

What flaws do I have, as I'm sure I've got some.

Thanks Jack.

Please read the FAQ in this section of PF.

Zz.
 
  • #5
I think every object must have two parts of energy : the rest (mc^2) and the moving which is kinetic energy. Because mass can be converted to energy so light is just a special case when mass is converted to energy.
 
  • #6
ZapperZ said:
Please read the FAQ in this section of PF.

Zz.

Cool, didn't know that was there.
 

FAQ: Exploring the Physics of Light: Does it Have Mass?

1. Does light have mass?

No, light does not have mass. It is a form of energy that travels in the form of electromagnetic waves. These waves do not have any mass, unlike particles such as protons and electrons.

2. How is the mass of light measured?

The mass of light cannot be measured directly because it does not have mass. However, it can be measured indirectly by determining its energy using Einstein's famous equation, E=mc^2. This equation shows that mass and energy are equivalent, and thus the energy of light can be used to calculate its "effective mass".

3. Does light experience gravity?

Yes, light does experience gravity. According to Einstein's theory of general relativity, gravity is the curvature of spacetime caused by the presence of mass or energy. Since light has energy, it is affected by gravitational fields. This was confirmed by observations during the solar eclipse of 1919.

4. Can light be slowed down?

Yes, light can be slowed down in certain mediums such as water or glass. This is because these materials have a different refractive index than air, causing light to travel at a slower speed. However, light always travels at the speed of light in a vacuum, which is approximately 299,792,458 meters per second.

5. Does light have momentum?

Yes, light has momentum. According to the principles of quantum mechanics, light can be described as a stream of particles called photons. These photons have both energy and momentum, which can be transferred to other objects when they interact with light, such as in the case of solar sails.

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