Does Light Have Mass and Can It Travel at Light Speed?

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    Light Mass Physics
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Discussion Overview

The discussion revolves around the nature of light, specifically whether it has mass and how it can travel at the speed of light. Participants explore concepts related to energy, mass, and the implications of Einstein's equation E=mc². The conversation includes theoretical considerations and conceptual clarifications.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that light has mass, albeit a small amount, and questions how it can travel at the speed of light without requiring infinite energy.
  • Another participant proposes that energy has mass, which becomes significant at speeds close to light, and discusses how light can still perform work despite its speed.
  • A third participant distinguishes between "relativistic mass" and "invariant mass," explaining that invariant mass does not change with speed while relativistic mass increases as speed approaches light.
  • One participant posits that all objects have both rest energy and kinetic energy, suggesting that light represents a case where mass is fully converted to energy.

Areas of Agreement / Disagreement

Participants express differing views on the nature of mass in relation to light and energy, with no consensus reached on whether light has mass or how it relates to energy and speed.

Contextual Notes

Participants reference concepts such as relativistic mass and invariant mass, indicating potential misunderstandings or differing interpretations of these terms. The discussion also touches on the implications of energy conversion, which may not be fully resolved.

Foxcroft
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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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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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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)
 
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.
 
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.
 
ZapperZ said:
Please read the FAQ in this section of PF.

Zz.

Cool, didn't know that was there.
 

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