Speed of Light - Highest Possible Speed?

Click For Summary

Discussion Overview

The discussion revolves around the concept of the speed of light as the ultimate speed limit in physics, particularly in the context of special relativity. Participants explore hypothetical scenarios involving objects moving at relativistic speeds and the implications for velocity addition.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose a scenario where a train moves at 99% the speed of light and a race car on top of it moves at 2% of the speed of light, questioning whether this results in a speed exceeding the speed of light.
  • Others argue that velocities do not add in the same manner as in classical physics, referencing the principles of relativity.
  • A participant mentions the need for infinite energy to reach the speed of light, suggesting that the race car's speed would not exceed the speed of light due to relativistic effects.
  • Another participant introduces the concept of time dilation, suggesting that the race car's speed would appear slower than expected due to relativistic effects.
  • Some participants discuss the need for visual aids, such as animations, to better understand the concept of velocity addition in relativity.
  • A reference to Feynman's work is made, indicating that the addition of speeds requires specific equations from special relativity.

Areas of Agreement / Disagreement

Participants express differing views on the addition of velocities and the implications of relativistic physics. There is no consensus on the interpretations of the scenarios presented, and the discussion remains unresolved regarding the nature of speed limits in relativity.

Contextual Notes

Participants reference various principles of special relativity, including time dilation and the non-classical addition of velocities, without reaching a definitive conclusion on the implications of these concepts.

LDelta
Messages
2
Reaction score
0
Well the other day I was thinking about the speed of light and how physics says that nothing can go above the speed of light and that you need infinite energy to go at the speed of light. But take this example: Imagine this example, you're on a train going at 99% the speed of light (therefore energy required is < infinity) and you put a race car on top of the last wagon on the train and have it go at 2% (once again energy required is < infinity) of the speed of light, wouldn't you technically be going at 101% of the speed of light? Is the speed of light truly the limit?
 
Physics news on Phys.org
LDelta said:
Well the other day I was thinking about the speed of light and how physics says that nothing can go above the speed of light and that you need infinite energy to go at the speed of light. But take this example: Imagine this example, you're on a train going at 99% the speed of light (therefore energy required is < infinity) and you put a race car on top of the last wagon on the train and have it go at 2% (once again energy required is < infinity) of the speed of light, wouldn't you technically be going at 101% of the speed of light? Is the speed of light truly the limit?

Shouldn't matter. The racecar is initially going 99% the speed of light, since it is on this train. It would need an infinity amount of energy to go 1% faster.
 
LDelta said:
you're on a train going at 99% the speed of light (therefore energy required is < infinity) and you put a race car on top of the last wagon on the train and have it go at 2% (once again energy required is < infinity) of the speed of light, wouldn't you technically be going at 101% of the speed of light?

No. Velocities don't "add" the same way in relativity that they do in classical physics:

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/einvel.html
 
Somebody needs to make a nice animation with hyper-rotations of world lines to show how velocity addition works due to a non-positive definite metric.

Other than that, what you need to keep in mind is that everything is always traveling at the speed of light, but through both space and time. An object at rest propagates only along the time axis. An object in motion can then have at most the speed of light as its observed local velocity. In observer's rest frame, time axis is always pointing along the observer's own world-line. Hence the need for rotations to explain velocity addition.
 
Read Feynman's Six Not So Easy Pieces, it has a very nice solution to this
You can't just add the speeds, you have to put it twice through the equation for special relativty, and as long as the components don't equal the speed of light, how they relate won't either.
 
LDelta said:
Well the other day I was thinking about the speed of light and how physics says that nothing can go above the speed of light and that you need infinite energy to go at the speed of light. But take this example: Imagine this example, you're on a train going at 99% the speed of light (therefore energy required is < infinity) and you put a race car on top of the last wagon on the train and have it go at 2% (once again energy required is < infinity) of the speed of light, wouldn't you technically be going at 101% of the speed of light? Is the speed of light truly the limit?

Well, actually, that is exactly why Einstein said time slows down. When time in the racecar slows down, the racecar cannot go at 2% of the speed of light, so relative to the time outside, the racecar is going slower than 2% of the speed of light, but I have proven that there is a commonly known mysterious massive particle (don't worry its not the tachyon) that can go at any speed it wants and have given my reasoning with gravity.
 
K^2 said:
Somebody needs to make a nice animation with hyper-rotations of world lines to show how velocity addition works due to a non-positive definite metric.

I've seen one you might be interested in. The www.lerner.org website has the old The Mechanical Universe series, which has some excellent (basic) graphicals on relativity theory, amongst a wealth of other fields. The web link is this ...

http://www.learner.org/index.html"

You'll be asked to register, but it's all free. The videos may be viewed on your PC screen, and in full screen if selected. The Mechanical Universe & Beyond series is at this shortcut ...

http://www.learner.org/resources/series42.html"

The episodes that relate to relativity theory are these ...

41 The Michelson-Morley experiment

42 The Lorentz Transformation

43 Velocity and Time

44 Mass, Momentum, Energy

It's either episode 42 or 43, I think 43, that presents the animation on relativity's Composition of Velocites.

GrayGhost
 
Last edited by a moderator:

Similar threads

  • · Replies 21 ·
Replies
21
Views
5K
  • · Replies 130 ·
5
Replies
130
Views
17K
  • · Replies 15 ·
Replies
15
Views
2K
  • · Replies 45 ·
2
Replies
45
Views
5K
  • · Replies 20 ·
Replies
20
Views
2K
  • · Replies 45 ·
2
Replies
45
Views
7K
  • · Replies 12 ·
Replies
12
Views
2K
  • · Replies 22 ·
Replies
22
Views
2K
  • · Replies 15 ·
Replies
15
Views
3K
  • · Replies 10 ·
Replies
10
Views
2K