Speed of light

[tarak]

This may sound innocent to physicists and astronomists??I understand time has a directionality and cannot be reversed.I read somewhere that if you break the speed of light barrier;you can travel back in time.Is this true???? anybody explain this to me in simple terms.

[Buffy]

An incredibly oversimplified explanation: Einstien's equations have time slowing down as you approach the speed of light. It goes to zero at the speed of light, and the numbers for the time term start going "negative" (a gross simplification mathematically, but basically true), when the speed term of the equation is increased past the speed of light. The little problem is getting past the speed of light without actually hitting it: Unless you convert yourself into energy, it takes an infinite amount of energy to reach the speed of light and your mass becomes infinite, none of which is either desireable or even really possible.

 

Relativistically,

Buffy

[paultrr]

There are three main parts to relativistic effects:

 

1.) Time dilation.

 

2.) Length contraction.

 

3.) Relativistic mass increase.

 

As for can time run backwards that has been an often debated subject in physics. Guys like Gott and Thorne say its possible for time to run backwards. Guys like Hawking say no. The general arguments against time running backwards stems from what we call cause and effect. Its also true that it would take an infinite amount of energy to accelerate something to the speed of light in our spacetime.

[hefner]

There are three main parts to relativistic effects:

1.) Time dilation.

2.) Length contraction.

3.) Relativistic mass increase.

Something is amiss from that list: numbers 1 & 2 are meaningless by themselves, but fit hand-in-glove with a third SR effect, clock dissynchronicity. Considering 1 & 2 alone, without that other, would result in self-contradiction as regards the twin paradox.

 

As for mass increase, it is indeed relativistic, not absolute, since an object's speed is never absolute. So I greatly prefer to attribute the inability of fast-as-light motion to the unusual way that velocities add. When rocket engine propulsion is employed, you have thrust originating in the object's very own rest frame, so it cannot labor extra from any supposed mass increase.

[maddog]

I read somewhere that if you break the speed of light barrier;you can travel back in time.Is this true???? anybody explain this to me in simple terms.

Simple answer... No.

 

Of course I am answering no to ... "breaking the speed of light barrier". This is

definitely, NO! At least, to the breaking. Negative time as you refer to would only occur

with "theoretical" particles such as Tachyons. There is no proof at the moment these

particles exist. Now as for Time reversals as paultrr stated, there is a controverersial

topic that Antimatter can behave in short time intervals as though time is Time is

reversed. Read a book called "Time's Arrow, Archimedes Point". I forget the author.

There is another one by Paul Davies on "Beyond Time" is good too. They explain it

better than I would. The point is, we are talking about what small particles would do

and not what big objects as people would do in this case.

 

Hope this was simple enough... :Alien:

 

Maddog

[Aki]

Example of antimatter, time reversal:

An electron traveling forward in time is equivalent to a positron traveling backwards in time.

[Qfwfq]

The matter of PCT is often and very easily misinterpreted. A fermionic line with its arrow going from vertex A to vertax B of a Feynman diagram represents either the fermion going that way or its anti going from vertex B to vertex A.

 

If the diagram is viewed in configuration space with A at a time previous to B, then the first of the two things is the sensible interpretation. If vertex B is at a time previous to A then it's the other one, the antifermion going from B to A.

 

I regret not having much time to discuss the whole matter, the real way to see it involves the minkowskian geometry of space time and it is very often explained somewhat loosely.

I read somewhere that if you break the speed of light barrier;you can travel back in time.Is this true???? anybody explain this to me in simple terms.

If two events are separated by a spacelike interval (velocity greater than c) then, in the coordinates of some observers they will be at the same time, for others one will be previous to the other, and vice versa for yet other observers. Note: I'm talking about SR, not GR, and these observers are meant to be inertial.

 

The conclusion is that, if one of these two events could influence the other, this cause-effect would be forward or backward in time, or instantaneous, according to different inertial observers. Not a matter of an object passing from less than c to more than c.

 

This explanation certainly isn't simple to understand but, unfortunately, any simpler argument is really unsatisfactory and typically misleading.