Confused on how nothing can be faster then light

[Cyclopsicle]

I'm confused on how it would be impossible to be faster then light, is it your acceleration? or is it how fast you are going in comparison to some other frame of reference (I do see that phrase being thrown around here)? Because if 2 objects are moving towards each other at more than half the speed of light, doesn't it mean that in respect to each other it is moving faster then c?

 

[StukaJU87c]

The problem with any type of matter traveling at or near the speed of light is that as speed increases, so does mass. At the speed of light mass would become infinite and thus require infinite propulsion and there are just all sorts of problems with that.

Not to mention faster than light travel would in theory cause one to travel back in time which violates causality. Explanation as to why traveling into the past doesn't work is rather obvious and circular to explain.

 

[Cyclopsicle]

ok, but what if two objects are moving towards each other at more than half c, in reference to a body at rest, wouldn't the objects be traveling more than the speed of light in reference to each other?

 

[StukaJU87c]

This I'm not entirely sure about here's how it seems to me:

Yes, say they are both traveling at 60% of c. In reference to object A, object B would be traveling towards it at 120% of c and vice versa, however neither has actually exceeded the speed of light. They would both be experiencing the same amount of time dilation and length contraction. In reference to the speed of light being a cosmological speed limit, I believe the only reference frame that matters is that of a body at rest.

 

[Cyclopsicle]

Yes but couldn't you pick one of the objects as the reference frame and see the other object exceeding the speed of light?

 

[StukaJU87c]

It would be more or less an illusion. What matters here is that nothing with mass can travel at or faster than 299,792,458 m/s. Both object A and B (at 60% of c) are traveling at 179,875,474 m/s. Neither has truly exceeded the speed of light, even if it seems as such from either perspective.

 

[jtbell]

what if two objects are moving towards each other at more than half c, in reference to a body at rest, wouldn't the objects be traveling more than the speed of light in reference to each other?

Velocities don't "add" in relativity the same way that they do in non-relativistic mechanics.

General information:
http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/einvel.html

Relative velocity of two objects moving towards each other:
http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/einvel2.html#c2

 

[algebrat]

If two objects are moving at each other, their relative velocity is not computed the way you are thinking. You have to use the formula for adding velocities. You're instinct to simply combine the velocities is a result of our everyday experience with nonrelativistic speeds.

http://math.ucr.edu/home/baez/physics/Relativity/SR/velocity.html

 

[HallsofIvy]

Specifically, if you observe two objects moving directly toward you at 60% the speed of light, then each, relative to the other, has speed
\frac{.6c+ .6c}{1+ \frac{(.6c)^2}{c^2}}= \frac{1.2c}{1.36}= .88

So each would see the other as approaching at 88% the speed of light, not 120% the speed of light.

 

[phinds]

... if you observe two objects moving directly toward you ...

Halls clearly meant towards EACH OTHER

 

[harrylin]

I'm confused on how it would be impossible to be faster then light, is it your acceleration? or is it how fast you are going in comparison to some other frame of reference (I do see that phrase being thrown around here)? Because if 2 objects are moving towards each other at more than half the speed of light, doesn't it mean that in respect to each other it is moving faster then c?

Most of the answers were probably given quite recently on this forum, for example here:
https://www.physicsforums.com/showthread.php?t=620279

and here (ongoing discussion):
https://www.physicsforums.com/showthread.php?t=641102

In what way are your questions different from those?

 

[HallsofIvy]

Halls clearly meant towards EACH OTHER

Actually, in order not to worry about angles, I was thinking of the situation in which "you" are standing directly between two objects, each moving toward "you" with speed, relative to "you", of .6c.

 

[EBENEZR]

If, for whatever reason, you traveled faster than the speed of light relative to another individual, would you not merely experience situations before the other individual has had a chance to catch up? Much like that early episode of Red Dwarf, you wouldn't be traveling back in time, but in fact in front of other people's time?

For that matter, does the fact light is limited to a certain velocity, time travels at a particular velocity also? Time is not in fact instantaneous, rather time travels at ~299x10^6m/s?

 

[Dale]

If, for whatever reason, you traveled faster than the speed of light relative to another individual, would you not merely experience situations before the other individual has had a chance to catch up? Much like that early episode of Red Dwarf, you wouldn't be traveling back in time, but in fact in front of other people's time?

Yes, according to FICTION like Red Dwarf that is exactly what happens. Different fiction authors may do it differently.

However, this forum is for discussing SCIENCE. The premise of your question is wrong; no massive object can travel at or faster than light locally. That is all that science can say about it.

 

[harrylin]

[..] For that matter, does the fact light is limited to a certain velocity, time travels at a particular velocity also? Time is not in fact instantaneous, rather time travels at ~299x10^6m/s?

Time: https://www.physicsforums.com/showthread.php?t=643834

 

[HallsofIvy]

If, for whatever reason, you traveled faster than the speed of light relative to another individual

The problem is that you are effectively saying "If relativity we not true, what would relativity say about this situation?" If relativity is not true (if you CAN travel faster than light), then relativity wouldn't say anything about! You have to fall back to Newtonian physics which says that it is possible to travel faster than light but nothing can travel back in time.

, would you not merely experience situations before the other individual has had a chance to catch up? Much like that early episode of Red Dwarf, you wouldn't be traveling back in time, but in fact in front of other people's time?

For that matter, does the fact light is limited to a certain velocity, time travels at a particular velocity also? Time is not in fact instantaneous, rather time travels at ~299x10^6m/s?

 

[EBENEZR]

Sorry! I'm new to all this, I know the rules of the forum but I don't know physics that well. In my defence, everything I said was a question.