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can something be observed (for lack of a better word) to be traveling faster than the speed of light?
ok so i was looking at the following page (http://www.phys.unsw.edu.au/einsteinlight/jw/modul... trying to get my head around relativity and i noticed that when looking at joes frame of reference he recieves the message from jane from year 3 in year 6.75ish and travels back by year 8 resulting in what appears to be 2.67 ly travel in just 1 and a bit year,
or is this not what is ment by nothing can travel faster than light?
im guessing the above statement only applys if i adjust for the time it had to of taken for the light to reach me
2 Answers
- Anonymous10 years agoFavorite Answer
The "faster than the speed of light" thing occurs because you take a measure in one frame, and apply a measure from another frame. This is called a "frame jump".
When you are up to speed, if you measure the distance traveled, it is contracted by gamma from what it is in the rest frame. Similarly, your duration will be "dilated" by the same amount... so the net is you and the rest frame both agree on your speed (as less than c).
If you were to travel to a point 1 light year away, at 0.866 c (gamma = 2), you would arrive at that point at the same time as light signals that left the starting point time of 0.155 years into your journey (a full year's worth is queued up and in transit to you), with an elapsed ship's time of 0.577 years. If you flipped around and headed back at the same speed, you would arrive at 2.309 years on the starting point's clock, and half that on yours. Neglecting acceleration effect.
You just have to keep measurements in one frame.
Here is an example of a frame jump:
http://www.fourmilab.ch/documents/OhMyGodParticle/
..." from the Andromeda galaxy to here in 3.5 minutes of proper time."
... and no, any measurement will show that it travels (just) less than c at any point in its path.
- OldPilotLv 710 years ago
It was observed in the late 1800s that light traveled at a constant speed regardless of the motion of the instrument making the measurement. At the same time James Maxwell wrote the Maxwell Equations that perfectly describe electromagnetism. Light is part of the electromagnetic spectrum. One result of the Maxwell Equations is all EM travels at a constant speed
Einstein took these 2 facts and asked, "How can that be true? In our normal experience velocities add and subtract.". The only way that it can be true is if space and time expand and contract with speed to make it true. Only way!
Another thing that must be true: Nothing with mass can reach or exceed the speed of light. So something like a laser dot can move faster than the speed of light but the photons that make up the dot do not
This means that if you travel at a significant fraction of the speed of light time slows down. When viewed from outside things really happen slower