It sounds like the stuff of science fiction, but spaceships that travel at warp speed are possible, according to one top scientist. Meteor traveling at 42,000mph rattles Vermont buildings Nasa rover releases its first audio clips from Mars And there is no absolute now.Biggest asteroid to make ‘close approach’ to Earth this year is 3,000ft wideĬhina and Russia to build Moon base together – and may ban US astronauts So such a thing is not permissible, and does not happen according to physics as we understand it. In that case, how did she receive a reply to a message that she never sent?Īnything that allows information to travel to the past causes paradoxes like this and the grandfather paradox, among others. She could send a message to herself at 2 seconds, to not the send the message to BOB at 4 seconds. If this was permissible, Alice could use Bob to send messages to herself in the past. She would receive the reply BEFORE she sent the message at 4 seconds. That means Alice would receive the reply at her 2 seconds. This means that the signal from Alice would have to travel back in time to reach Bob.īecause Bob receives the signal at 2 seconds, he could read the signal and reply at his 4 seconds using the same instantaneous “subspace” signal. But her clock is running slower than Bob’s from Bob’s perspective. But from Bob’s perspective, Bob receives the signal at 2 seconds, when Alice’s clock was at 4 seconds. It would arrive to Bob when his clock reads 2 seconds. Here’s how this would break causality: Alice sends a message to Bob using an instantaneous signal to Bob at her 4 seconds. And it is Alice’s clock that is running at ½ the speed of Bob’s clock. So from Bob’s perspective his clock is running normally. Bob’s clock will be moving at half the rate of Alice’s due to Bob’s speed relative to Aliceīut from Bob’s perspective, he is not moving, and the earth is moving away from him at 0.87c. Her clock on her world line will tick normally for her. The world line for Alice will be straight up, because she will not be moving in her frame of reference, but she will be moving forward in time. The now depends on the reference frame.įor example, imagine Alice on earth, and Bob in a rocket traveling 0.87c towards Proxima Centauri, our nearest neighboring star. What’s happening “right now” depends on how fast, and in which direction you’re moving. What if we kept special relativity, but we allowed faster than light communication, for example like instant subspace communication like in Star Trek? The problem is that in special relativity, it is not clear what instantaneous means. There would be no waves, and thus, no light. But if you set c equal to infinity, it would mean that these interactions of electricity and magnetism would not happen. Permittivity is the resistance of free space to the formation of electric fields, and permeability is the formation of a magnetic field by an electric current. c equals one over the square root of the permittivity and permeability of free space. The other problem is that we would not have light at all. Postulate 2: The speed of light in a vacuum is constant, and independent of the motion of the source of that light.īut what if this maximum speed was infinite, implying that the speed of light is infinite? For one thing using the equation E=MC^2, it would require an infinite amount of energy to accumulate any mass in the universe. Postulate 1: The laws of physics are the same in every reference frame. Neither of the postulates state that FTL is impossible. Without mass there is no restriction on its velocity.Įinstein’s theory of special relativity is based on two postulates. Light in a vacuum travels at c, the maximum speed because photons are massless. You can’t send information faster than the force field can change. The speed of information is the speed of a force field. What are the implications of having a speed limit on causality? Why is there a limit in the first place? And how would causality be broken if information could travel faster than light. A cause cannot have an effect anywhere in the universe faster than the speed of light. The maximum speed limit is not a limit with which things can move, but is a limit on the speed of causality. If you point a powerful laser at the moon, and spin it 100 times per second, the dot on the moon will move 3X the speed of light. 6:22 – What if speed of light was infinite?Ĩ:29 – What if we could send instantaneous subspace signals?
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