Is the speed of light truly unattainable?

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Discussion Overview

The discussion revolves around the nature of the speed of light, particularly whether it can be achieved or surpassed. Participants explore concepts related to special relativity, the properties of photons, and the implications of mass in relation to speed. The conversation includes theoretical considerations, personal beliefs, and references to scientific principles.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants propose that the speed of light cannot be achieved due to the concept of mass increasing as an object approaches light speed, suggesting an asymptotic relationship.
  • Others argue that photons have zero rest mass and therefore travel at the speed of light by definition, challenging the notion that they gain mass at speed.
  • A participant questions how light can be said to not achieve the speed of light, indicating confusion over the definitions involved.
  • There is a discussion about whether some photons can travel faster than others, with a clarification that all photons travel at the speed of light in a vacuum, but their effective speed can change in different media.
  • Some participants reference Cerenkov radiation as an example of particles exceeding the speed of light in a medium, while emphasizing that this does not apply to the speed of light in a vacuum.
  • Clarifications are made regarding the distinction between rest mass and relativistic mass, with some participants asserting that the concept of mass increasing with speed does not apply to photons.
  • There are calls for participants to provide reasoning for their beliefs rather than simply asserting them, highlighting the need for evidence in discussions.

Areas of Agreement / Disagreement

Participants express multiple competing views on the nature of light and speed, with no consensus reached on whether the speed of light can be achieved or the implications of mass in this context. The discussion remains unresolved with ongoing debate.

Contextual Notes

Participants express differing interpretations of mass in relation to speed, and there are unresolved questions about the implications of light traveling in different media versus a vacuum. The discussion also reflects varying levels of understanding of special relativity and its principles.

Rubix
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I currently believe that the speed of light cannot be achieved. Even light itself is not as fast as the speed of light. Technically, a photon gains some mass as it has speed, although it is extremely small, and as things with mass get closer and closer to the speed of light, their mass gains because of the energy, and gains infinite weight so that the speed of light cannot happen. To better explain this, think of a graph. The X-axis being matter, and the Y-axis being speed. Think of there being an asymptote somewhere on the graph. The mass can never reach that speed, but it can get very so close, even with a force being applied to the mass, that force would be converted to weight.

any comments?
 
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No.

For one, what you believe is completely irrelevant. Both to the truth and to any discussion taking place here at PF. Personal theories are not allowed, especially ridiculous ones such as this.

Second, photons have identically zero rest mass, not very close to zero. Exactly zero.

Third, by the way you speak about this belief of yours, you don't understand special relativity very well. So please do not make such outlandish statements when your knowledge of the topics is so limited. If you want to ask questions, that is one thing. But do not assert claims.
 
I do have one comment. How can light not achieve the speed of light?
 
< editorial cut by staff >

photons DO have zero mass at rest. But when they are at their constant speed, they gain mass, slight mass. < editorial cut by staff >

"what you believe is completely irrelevant... to any discussion taking place here at PF"
Now that is just dumb.
 
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Nabeshin is correct. Photons are energy packets, they have a quantum of energy/momentum. They do not have any mass and thus are not affected by the factor \gamma which incorporates the ratio of the speed to c that normally causes energy to become infinite for particles of mass as they approach c.
 
is it correct that some photons travel faster than others?
 
Rubix said:
is it correct that some photons travel faster than others?

No, all photons travel at the speed of light. When traveling in a medium, the photons still travel at the speed of light but the cumulative speed of the electromagnetic wave is altered due to the absorption and emission of the photons by the medium's atoms and phonons.
 
Please let us calm down - at PF we don't allow personal insults.

To the OP: you are confusing two kinds of "masses": rest mass and what's sometimes called "relativistic mass", which is nothing else but total energy (including kinetic energy).

Photons in vacuum do travel at the speed of light (by definition, I'd say), and there's no problem with any "mass increasing as they get faster". In fact, photons in vacuum cannot travel at anything else but at light speed. Their "relativistic" mass is given by their energy (the frequency of the radiation), but this doesn't hinder in any way them to reach light speed (in fact they never "reach" light speed, as they never go slower: light doesn't accelerate in vacuum).

What you are describing, however, is correct for particles with non-zero REST mass. It is true that their relativistic mass (their total energy) becomes infinite if they would reach light speed, so you'd need infinite energy to accelerate them from a lower speed to light speed.
 
light traveling at the speed of light is a very important fact that bases all the laws of relativity. Yet you try to use relativity to contradict the fact that photons travel at the speed of light.

Now think about what you did.
 
  • #10
I guess standard models say that photons have exactly zero rest mass. In that case of course photons can only travel at exactly the speed of light just by definition. And zero mass multiplied by a relativistic factor is still zero mass.

If someone ever found that photons have some rest mass, then the limiting speed wouldn't be the speed of the photon, indeed.

Nabeshin said:
For one, what you believe is completely irrelevant. Both to the truth and to any discussion taking place here at PF. Personal theories are not allowed, especially ridiculous ones such as this.
...
So please do not make such outlandish statements when your knowledge of the topics is so limited. If you want to ask questions, that is one thing. But do not assert claims.
I hope you have used the time to think about your own statements, Nabeshin. That's not just equations, but also people here. If you do not understand what I mean, show that post to non-physics friends of yours and ask what they think.
 
  • #11
Quote from an article that states that particles traveling at a speed greater than the speed of light, thus is it possible to travel faster than the speed of light, comments please.

"This radiation, as you pointed out, comes from particles traveling at a speed greater than the speed of light in the medium in which they are moving. The explanation we have adopted for Cerenkov radiation was first given by Tamm and Franc. To clarify your question a little, only electrically charged particles emit Cerenkov radiation."

http://www.physlink.com/Education/AskExperts/ae219.cfm
 
  • #12
JWDeanIII said:
Quote from an article that states that particles traveling at a speed greater than the speed of light, thus is it possible to travel faster than the speed of light, comments please.
When folks talk about particles not being able to travel faster than the speed of light, they generally mean the speed of light in a vacuum (3 x 108 m/s), not the speed of light in some medium (which is less).
 
  • #13
JWDeanIII said:
"This radiation, as you pointed out, comes from particles traveling at a speed greater than the speed of light in the medium in which they are moving. The explanation we have adopted for Cerenkov radiation was first given by Tamm and Franc. To clarify your question a little, only electrically charged particles emit Cerenkov radiation."
The speed of light in some medium is not the speed limit. The speed of light in vacuum is.
 
  • #14
Rubix said:
< editorial cut by staff >

photons DO have zero mass at rest. But when they are at their constant speed, they gain mass, slight mass. < editorial cut by staff >
What reason do you have for saying this? If a particle has rest mass m_0 then it "relativistic mass", at speed v relative to the measuring device, is m_0/\sqrt{1- v^2/c^2}[/itex, slightly larger than m_0- <b>except</b> if m_0= 0. 0 divided by any non-zero number is still 0.

"what you believe is completely irrelevant... to any discussion taking place here at PF"
Now that is just dumb.
I think he was saying that simply asserting that you "believe" something- without giving any reason for believing it or giving evidence doesn't help. Please tell us why you believe that!
 
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  • #15
HallsofIvy said:
I think he was saying that simply asserting that you "believe" something- without giving any reason for believing it or giving evidence doesn't help. Please tell us why you believe that!

Yes, this is what I meant. I apologize for coming off a little strong in my previous post, that was unfair. Hopefully the others have answered your question adequately.
 
  • #16
Excuse me for asking this, but why can particles in a medium travel faster than the speed of light and in a vacuum they can not?
 
  • #17
JWDeanIII said:
Excuse me for asking this, but why can particles in a medium travel faster than the speed of light and in a vacuum they can not?
Replace the phrase "faster than the speed of light" with the phrase "faster than 3 x 108 m/s" (which happens to be the speed of light in a vacuum). Particles cannot travel faster than 3 x 108 m/s.
 
  • #18
Rubix said:
I currently believe that the speed of light cannot be achieved. Even light itself is not as fast as the speed of light. Technically, a photon gains some mass as it has speed, ...

The "gain" in mass happens because the rest mass is multiplied by the factor,

1/√[1 - (v/c)2]​

to come up with the relativistic mass.

A photon's rest mass is zero. So multiplying by that factor, for
any speed less than c, would still give zero relativistic mass.
 

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