How would the speed of light affect your mass?

  • Thread starter Bonkenhi
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(This is probably answered somewhere, but I couldn't find it, I'm kinda new. >_>)

So, say I was able to travel at the speed of light. My teacher told me once if you were say, running, you'd weigh a slight, unoticable amount more. (Or I just wasn't listening right. >_>)
Anyways, would traveling at the speed of light raise your mass by like, 1000's of times? Or have I got this completely wrong? =/
 

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  • #2
Your teacher is right. You are wrong (partially, right idea though :)). When traveling the speed of light, your mass becomes infinite and your size (in the direction of thrust) becomes infinitely small (0). If you want a more in depth solution/read, read up on Einstein's theory of relativity.
 
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  • #3
berkeman
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Your teacher is right. You are wrong (partially, right idea though :)). When traveling the speed of light, your mass becomes infinite and your size (in the direction of thrust) becomes infinitely small (0). If you want a more in depth solution/read, read up on Einstein's theory of relativity.
Read about the Lorentz Factor part-way down this intro page at wikipedia.org:

http://en.wikipedia.org/wiki/Special_relativity

As an object moves faster and faster, its mass increases. That's why it would take an infinite amount of energy to accelerate a material object to the speed of light (can't be done).
 
  • #4
Ahhh, yes. I've always wondered though, its not possible to have something reach the speed of light with mass, what about having a negative mass (entirely theoretical speaking)?
 
  • #5
berkeman
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Ahhh, yes. I've always wondered though, its not possible to have something reach the speed of light with mass, what about having a negative mass (entirely theoretical speaking)?
I don't think negative mass is a theoretical subject -- I believe mass is always zero or positive. And we don't discuss overly speculative concepts here on the PF, please keep that in mind.

Photons are an example of an object that travels at the speed of light. It can do that because it has zero "rest mass". See the comments about photon mass part-way down this intro page for photons:

http://en.wikipedia.org/wiki/Photon
 
  • #6
What about tachyons? With their imaginary mass? One of the things I have been trying to grasp lately is, what is an imaginary mass? is it negative? or what?
 
  • #7
berkeman
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What about tachyons? With their imaginary mass? One of the things I have been trying to grasp lately is, what is an imaginary mass? is it negative? or what?
I dunno. Tachyons are hypothetical particles. Pretty fun to read about though...

From http://en.wikipedia.org/wiki/Tachyon

wikipedia.org said:
A tachyon (from the Greek ταχυόνιον, takhyónion, from ταχύς, takhýs, i.e. swift, fast) is any hypothetical particle that travels at superluminal speed. The first description of tachyons is attributed to German physicist Arnold Sommerfeld; however, it was George Sudarshan, Olexa-Myron Bilaniuk[1][2], Vijay Deshpande[2] and Gerald Feinberg[3] (who originally coined the term in the 1960s) that advanced a theoretical framework for their study. Tachyonic fields have appeared theoretically in a variety of contexts, such as the Bosonic string theory. In the language of special relativity, a tachyon is a particle with space-like four-momentum and imaginary proper time. A tachyon is constrained to the space-like portion of the energy-momentum graph. Therefore, it cannot slow down to subluminal speeds. Even if tachyons were conventional, localisable particles, they would still preserve the basic tenets of causality in special relativity and not allow transmission of information faster than light[3].
 
  • #8
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what about in space. what is speed compaired to in space? since there is nothing in space, just a vacuum, so nothing could slow you down, if you had enough fuel or whatever, wouldn't you keep accelerating? theres nothing to stop you from going faster, no resistance, so wouldn't you be able to get going the speed of light or faster? of course it would be incredibly inefficient, but would it theoretically work? prob not, but just curious
 
  • #9
No it would not theoretically work because the theory of general relativity states that as you approach relativistic speeds your mass eventually becomes infinite, this would mean that you would need an infinite amount of energy to move an infinite mass. Also, when you approach relativistic speeds your size in the direction of thrust becomes smaller and smaller, and when you reach the speed of light, it becomes 0, which is impossible. Two reasons why going the speed of light, no matter where you are is impossible. But keep dreaming up crazy schemes.
If we do not imagine the impossible, we cannot achieve the impossible.
(That was said by a guy I know) :D
 
  • #10
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I don't think negative mass is a theoretical subject -- I believe mass is always zero or positive. And we don't discuss overly speculative concepts here on the PF, please keep that in mind.
Negative mass has been discussed theoretically in the physics literature. A well known paper on this topic is

Negative Mass in General Relativity, Herman Bondi, Rev. Mod. Phys, 29(3), July 1967

Also its conceivable that there is negative mass in the universe which is causing its expansion to increase at an accelerating rate. Negative pressure or a positive cosmological constant will produce an antigravity affect. The effective mass density of a large enough negative pressure (i.e. tension) will produce a negative active gravitational mass. A vaccum domain wall produces a repulsive gravitational field. This is due to a negative active gravitational mass density.

As far as negative inertial mass goes, its concievable that if you place enough tension in a rod then the rod's inertial mass will become negative. In practice I believe that the rod would break far before that amount of stress is induced.

Pete

ps - I can E-mail the Bondi article to anyone who sends me their e-mail address and a request to do so.
 
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