Quizzes & Puzzles5 mins ago
Time Travel, Teleportation Or Traveling Faster Than The Speed Of Light
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Which of these will be achieved first, 2nd and 3rd and what do you base your choices on?
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I'm certainly no expert in these matters - in fact consider myself in "relative" terms to be a simpleton myself.
By "4-velocity" jim means the four-dimensional spacetime vector that describes the path of an object moving through spacetime. Because space and time are individually known not to be absolute (i.e. constant from the point of view of all observers) spacetime measurements are a way of achieving a measurement that CAN be agreed on. So in this context you can't have displacement by space or time individually, only direction in spacetime. And the universal speed (which happens to be the speed light travels at) is used as a constant for all objects. Remember that we traditionally think of "speed" as rate of displacement in three dimensions, but in spacetime that classical idea of displacement does not apply.
So an object at rest only travels through time, while conversely an object travelling at the speed of light does not displace itself in time, which literally stands still for it!
By "4-velocity" jim means the four-dimensional spacetime vector that describes the path of an object moving through spacetime. Because space and time are individually known not to be absolute (i.e. constant from the point of view of all observers) spacetime measurements are a way of achieving a measurement that CAN be agreed on. So in this context you can't have displacement by space or time individually, only direction in spacetime. And the universal speed (which happens to be the speed light travels at) is used as a constant for all objects. Remember that we traditionally think of "speed" as rate of displacement in three dimensions, but in spacetime that classical idea of displacement does not apply.
So an object at rest only travels through time, while conversely an object travelling at the speed of light does not displace itself in time, which literally stands still for it!
I think it's one of those mathematically true statements that is also annoyingly misleading. Here is my own explanation:
I'll stick to Special Relativity, "SR", but the arguments below can be extended to General Relativity.
What separates SR from Newton's mechanics most clearly is what is treated as "invariant under transformation". Relativity exists in Classical mechanics too, but with a different transformation. In this world the invariants are time and length separately -- where length is calculated using Pythagoras' Theorem.
In SR, these two are combined of course, so that time and length are together invariant in the "four-length" s, with s^2 = (speed of light * time)^2 - length^2, or:
s^2 = (ct)^2 - L^2
Now this length s has units of distance, and is also invariant under the transformation laws of SR, which are the Lorentz transformations. What is important is that once you have measured s for any particular situation, it takes that same value no matter how fast you are moving. In particular, if you are moving at a speed such that the length measured (or strictly the change in length) is zero, then we have that:
s = ct => (s/t)^2 = c^2
This horrible abuse of notation is nevertheless correct in essentials (just change the notation to the correct one and be a bit more careful by what you mean by "time") and tells us that we can define something called "four-velocity" which is:
u = s/t with u^2 = c^2 = constant.
This value is also constant under transformations, so that all objects have a 4-velocity equal to the speed of light in spacetime.
There are two reasons I think this is misleading, though. Firstly, if you start defining this 4-velocity to be the only one that matters then a similar argument would lead to the startling conclusion that for light itself, u=0, so that light is stationary -- the only thing that doesn't "travel at the speed of light" is light!
Secondly, the fact that u^2 = c^2 alway for all massive objects is "merely" a statement that dynamics occurs in SR rather than Newton's theory. Marginally more important is the direction in which the four-velocity is pointing -- in other words, where something is going. Using u = 4-velocity, v = "normal velocity" and y as the lorentz factor (related to transformations,and depending on v), we have:
u^2 = y^2*(c^2 - v^2)
and to me the v carries more useful information about the motion of the particle. In particular it's the "v-velocity", rather than the u, that joins up best with Newton's theory of motion. And ultimately the point of SR is that it extends, rather than replaces, Newton's theories.
I don't know. It's all down to interpretation I suppose. The 4-velocity is important because you need to know what is invariant. The 3-velocity is important because you need to know where something is actually going.
And before people jump on me along the lines of "but surely the point is that all motion is relative!" -- yes, but not everything is stationary "at once", so that while no object can be said to be moving absolutely, all objects are moving with respect to something. And what that something is determines v. Since, usually, that something is us, we care about what v is rather more than what u is, since u is always the same anyway.
I'll stick to Special Relativity, "SR", but the arguments below can be extended to General Relativity.
What separates SR from Newton's mechanics most clearly is what is treated as "invariant under transformation". Relativity exists in Classical mechanics too, but with a different transformation. In this world the invariants are time and length separately -- where length is calculated using Pythagoras' Theorem.
In SR, these two are combined of course, so that time and length are together invariant in the "four-length" s, with s^2 = (speed of light * time)^2 - length^2, or:
s^2 = (ct)^2 - L^2
Now this length s has units of distance, and is also invariant under the transformation laws of SR, which are the Lorentz transformations. What is important is that once you have measured s for any particular situation, it takes that same value no matter how fast you are moving. In particular, if you are moving at a speed such that the length measured (or strictly the change in length) is zero, then we have that:
s = ct => (s/t)^2 = c^2
This horrible abuse of notation is nevertheless correct in essentials (just change the notation to the correct one and be a bit more careful by what you mean by "time") and tells us that we can define something called "four-velocity" which is:
u = s/t with u^2 = c^2 = constant.
This value is also constant under transformations, so that all objects have a 4-velocity equal to the speed of light in spacetime.
There are two reasons I think this is misleading, though. Firstly, if you start defining this 4-velocity to be the only one that matters then a similar argument would lead to the startling conclusion that for light itself, u=0, so that light is stationary -- the only thing that doesn't "travel at the speed of light" is light!
Secondly, the fact that u^2 = c^2 alway for all massive objects is "merely" a statement that dynamics occurs in SR rather than Newton's theory. Marginally more important is the direction in which the four-velocity is pointing -- in other words, where something is going. Using u = 4-velocity, v = "normal velocity" and y as the lorentz factor (related to transformations,and depending on v), we have:
u^2 = y^2*(c^2 - v^2)
and to me the v carries more useful information about the motion of the particle. In particular it's the "v-velocity", rather than the u, that joins up best with Newton's theory of motion. And ultimately the point of SR is that it extends, rather than replaces, Newton's theories.
I don't know. It's all down to interpretation I suppose. The 4-velocity is important because you need to know what is invariant. The 3-velocity is important because you need to know where something is actually going.
And before people jump on me along the lines of "but surely the point is that all motion is relative!" -- yes, but not everything is stationary "at once", so that while no object can be said to be moving absolutely, all objects are moving with respect to something. And what that something is determines v. Since, usually, that something is us, we care about what v is rather more than what u is, since u is always the same anyway.
We already live on a planet that is fast becoming over-populated'
If we were to find a way to live forever what would you propose to do about further procreation?
Would you ban it?
Would all of one sex ( either men or woman ) be sterilised at birth ?
If we were to live forever we definately could not carry on replenishing the human race at the rate that we do now.
If we were to find a way to live forever what would you propose to do about further procreation?
Would you ban it?
Would all of one sex ( either men or woman ) be sterilised at birth ?
If we were to live forever we definately could not carry on replenishing the human race at the rate that we do now.
Modern humans have been on the earth for around the last 200k years.
Who is to say what knowlege mankind will gain / what will be discovered , in the next 200k years - no one can .
We can only speculate currently on what we can envisage , given our current knowlege .
No one can say that any of the things in the op will not be possible in the future .
Tell me which part of the foregoing is incorrect .
Who is to say what knowlege mankind will gain / what will be discovered , in the next 200k years - no one can .
We can only speculate currently on what we can envisage , given our current knowlege .
No one can say that any of the things in the op will not be possible in the future .
Tell me which part of the foregoing is incorrect .
It's not incorrect per se, but I do think it's a bit misleading. We can provide a reasonable assessment of how likely, or not, certain new developments are, based on current understanding. So, as time travel, faster-than-light travel and teleportation appear to contradict Relativity and Quantum Mechanics, theories that have stood the test of a century of intense scrutiny and emerged triumphantly on the other side -- as the three things OP mentions above contradict, then, all current experimental knowledge, they really aren't that likely. Not impossible, perhaps -- but highly unlikely.
Well if you are going to take that argument to extremes why bother learning about current understanding at all -- since in 200k years it's all going to be wrong anyway?
The "we never know what's going to happen" argument is technically correct but shouldn't be used without at least also appreciating why we think the way we think today. There are very good reasons for thinking that all the things OP mentions are impossible, or at least highly implausible -- and they shouldn't be brushed aside lightly.
The "we never know what's going to happen" argument is technically correct but shouldn't be used without at least also appreciating why we think the way we think today. There are very good reasons for thinking that all the things OP mentions are impossible, or at least highly implausible -- and they shouldn't be brushed aside lightly.
I don't agree with that Bazile or not in the way it's intended
Fundamental observations of Universal physical laws are unlikely to change - maybe gravity will suddenly start running in reverse - I wouldn't try to base an argument on it though.
It's the same with Human technology - it's based on physical laws and that's unlikely to fundamentally change.
What does happen is that edge cases get resolved and sometimes they have remarkable applications but they don't change past physical laws in the domains in which they are observed.
So you have to seperate things that we have observed from what is inferred
The argument that you don't know what technology will bring is almost always based on where people have drifted past what is observed into what is inferred - or sometimes not even that.
Let's take an example a reducing ray that will shrink me to the size of a bacteria.
I think I can pretty confidently rule that out of future technology based on existing known and observed areas of science that are not going to be changed by existing technology
Fundamental observations of Universal physical laws are unlikely to change - maybe gravity will suddenly start running in reverse - I wouldn't try to base an argument on it though.
It's the same with Human technology - it's based on physical laws and that's unlikely to fundamentally change.
What does happen is that edge cases get resolved and sometimes they have remarkable applications but they don't change past physical laws in the domains in which they are observed.
So you have to seperate things that we have observed from what is inferred
The argument that you don't know what technology will bring is almost always based on where people have drifted past what is observed into what is inferred - or sometimes not even that.
Let's take an example a reducing ray that will shrink me to the size of a bacteria.
I think I can pretty confidently rule that out of future technology based on existing known and observed areas of science that are not going to be changed by existing technology
@ Jim and Ichkeria - Thanks for the explanations. A bit clearer what you were alluding to earlier now.
@bazile You are technically correct that no one can predict what the developments might be over a timespan of 200K years.
"Modern humans have been on the earth for around the last 200k years.
Who is to say what knowlege mankind will gain / what will be discovered , in the next 200k years - no one can ."
But when you compare where we are now and our understanding of nature, the universe and how it works, compared to our ancestors - not 200K years ago, but just 400 years ago, 100 even - We are starting at a completely different level.
I am not at all sure that there are any knowledge frontiers left, any "here be dragons" territory to our understanding of the fundamentals, and it needs that kind of leftfield principle to develop an applied technology like teleportation.
@bazile You are technically correct that no one can predict what the developments might be over a timespan of 200K years.
"Modern humans have been on the earth for around the last 200k years.
Who is to say what knowlege mankind will gain / what will be discovered , in the next 200k years - no one can ."
But when you compare where we are now and our understanding of nature, the universe and how it works, compared to our ancestors - not 200K years ago, but just 400 years ago, 100 even - We are starting at a completely different level.
I am not at all sure that there are any knowledge frontiers left, any "here be dragons" territory to our understanding of the fundamentals, and it needs that kind of leftfield principle to develop an applied technology like teleportation.
Some people like to invoke the idea that science changes and therefore the current limitations could be overcome. They often cite Einstein as showing Newton was "wrong".
In fact, like many aspects of modern science the new knowledge provided by Einstein did not in any way disprove Newton. Einstein simply showed that Newton's Laws were a special case of the deeper nature of reality, one where the speeds involved were trivial compared to the speed of light.
Moreover, in some ways Relativity can be considered as Newton's Laws in four dimensions.
Even General Relativity, which Einstein published ten years later is the general case in which Special Relativity is General Relativity applied to non-accelerating frame of reference.
Similarly, Quantum Mechanics did not throw out Atomic Theory but showed the underlying mechanisms.
In fact, like many aspects of modern science the new knowledge provided by Einstein did not in any way disprove Newton. Einstein simply showed that Newton's Laws were a special case of the deeper nature of reality, one where the speeds involved were trivial compared to the speed of light.
Moreover, in some ways Relativity can be considered as Newton's Laws in four dimensions.
Even General Relativity, which Einstein published ten years later is the general case in which Special Relativity is General Relativity applied to non-accelerating frame of reference.
Similarly, Quantum Mechanics did not throw out Atomic Theory but showed the underlying mechanisms.
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