Time goes differently for those on the ‘spaceship’ then on earth. For the people on the spaceship would it be possible to travel let’s say 10 light years in less than 10 years ‘ship time’ if traveling near the SoL?
Yes. To the question in the post rather than the subject title. Consider this rough qualitative example:
You set out for a star measured to be 10 light years away at .5c as measured by me on Earth. From my point of view the trip takes you 20 years. All the math works out perfectly.
But I also register that time moves slower for you, so you’re not experience 20 years passing, you are experiencing something less.
So do you then also experience your velocity relative to Earth and the destination as higher? No, you experience that as you accelerate the distance shrinks. The amount is shrinks is exactly opposite to the time dilation I measure for you.
Yes, it possible for spaceship to travel a 10 lyr distance (as measured in the Eathbound frame) in less than 10 years ship-time.
The time measured by observer travelling between two events must always be non-zero and it is the spacetime equivalent of their arc length between those two events. We cannot think of a light ray as an observer, but its arc length between two events is always zero and it represents the limit of how small the abslute value of the time between two events can be made. This means the time between two events as measured by an osberver travelling between them can always become arbitarily small.
And in fact, this notion (undilated distance per dilated time) is a useful enough one that it’s given its own name: “Proper velocity”. Use of proper velocity makes a lot of relativity calculations easier. For instance, if you’re experiencing acceleration, your proper velocity is changing at that rate per your proper time, no special relativistic accommodations needed (or at least, all of the relativistic bits cancel out). Accelerate at 1 g for 1 year, and you’ll have a proper velocity of 1 (it happens that 1 g is equal to c divided by a year). Accelerate at 1 g for 2 years, and you’ll have a proper velocity of 2. Accelerate at 5 gs for 4 years, and you’ll have a proper velocity of 20, and so on.
Why put the word relativistically in your question? That assumes that SRT is correct so the question becomes circular. Yes is the simple answer, but of course it has to be qualified. Various suggestions for the propulsion of a starship have been mooted, among them is using a light sail, so I will start with that one. The light from the Sun (assume that is the starting point) hits the sail and imparts a tiny push, so accelerating the starship. As the starship accelerates away, the force gets less and less, and at lightspeed this force becomes zero, so the starship cannot be accelerated any more. Impressive evidence for a lightspeed limit eh? No! The propulsive power is the light from the Sun, and that propulsive power is pushing the starship, so it cannot possibly push the starship faster than the speed of light. This is similar in essence to the reason that a cablecar is limited in its speed to that of the cable pulling it (Homer Tilton – “Today’s Take on Einstein’s Relativity” page 94, 2005). It is also the same as a particle in a particle accelerator. The particle is being pushed by an electro motive force, so cannot possibly be pushed faster than the speed of light. The situation is entirely different if the spaceship carries its own powerplant (rocket engine). The exhaust is propelled from the rear, and pushes the starship. No matter what the speed of the starship is relative to its starting point, the speed between the starship and its exhaust never changes, so the applied force and therefore the acceleration never changes (simplified by ignoring change of mass due to reduced fuel content).
Um, you’re basically saying that you don’t believe in Special Relativity, then ? That c is a speed limit of light, but not a speed limit of the universe ?
The other pertinent term here is “proper time”, which is the time measured by a clock in the moving spaceship. This is directly pertinent to the OP’s question since you can travel that 10 light-years in an arbitrarily small amount of proper time, given enough energy and thrust.
All of tomh4040’s previous posts are from 2012 in a thread titled “My problems with relativity”. I don’t remember exactly what his position was, but I have a guess I’m fairly confident about.
So “special” relativity"?
Assuming that special relativity is correct is an excellent assumption, because so far as absolutely every experiment ever has been able to determine, it is exactly and precisely correct to the limit of our ability to measure. We are literally more certain that special relativity is correct than we are about anything else in the Universe.
What if I put a second laser on a ship launched after the other? I keep this second ship above half of light speed, and it pushes the first ship to 1.5c.
Or what if I put them all on a treadmill and accelerate them to zero point nine nine repeating?
Checkmate!
The answer to OP’s question is YES, for some values of “theoretical”. An Alcubierre Drive should do the trick. Or, if that fails, then try an Infinite Improbability Drive.
Not checkmate Naita, not even check. This is a typical answer to be expected from relativitists - ignore the question (statement) posed, ask another one of your own, and answer that one. I am arguing against there being no cosmic speed limit (a phrase coined by Isaac Asimov, I think - I will not look it up). Your first sentence agrees with the statement and implies that there is no cosmic speed limit, and yet your second implies that there is.
You have mixed up the basic premises, there is no laser in my original post, just starlight. You have also forgotten Newton’s second law of motion, “every action has an equal and opposite reaction”. The second ship would be slowed down by the reaction of the laser, and as these ships have to be light and flimsy to be pushed by the minuscule force of the light, that reverse force would not be negligible.
Tom.
You’re saying there is a limit?
I think it is important to realise that a lot of the above is basically a naive misunderstanding of what special relativity says. Sort of taking a pop science “lies to children” view of what it is and finding fault.
It isn’t about the speed of light. It is much more basic. What is at core is the speed of causality. It just tuns out that massless particles are constrained to travel at the speed of causality and so photons travel at this speed.
The while idea of a cosmic speed limit is also just a pop science lies to children story. In special relativity everything travels at the speed of causality. If you are standing still you are travelling forward at one second per second. If you move, you stay travelling at this speed, but since you are now moving in space, you can’t travel forward at one second per second, and so your rate in the time dimension is slightly lower. You can use simple Pythagoras to solve the speeds in each dimension. Do that and you can derive Einstein’s famous E = mc^2 trivially. Similarly we can derive all the time dilation effects and predict things like nuclear energy.
Now things like nuclear energy actually exist and work as predicted, as do experimental observations of time dilation.
The burden of proof is rather set on coming up with a different predictive and falseifable theory that explains these results, rather than naive thought experiments that don’t match measured reality.
I am astounded that there is a derisory name for people who believe in the Theory of Relativity, I hope you don’t mind if I embrace that term gleefully. I can only guess that the ones who do not believe in Relativity are logically called absolutists, right? Well, if naita is right and you were an absolutist back in 2012 there is obviously no point in arguing with you: you are not willing to change your mind. Your post is so full of errors that it reminds me of a Gish Gallop. And you ignore facts like the relativistic mass increase, so that the same force exerted does not have the same accelerating effect on a given body when its speed increases. As I can only suppose that you deny the relativistic mass increase (otherwise your argument makes no sense) it is not possible to argue with you.
I only wonder why you want to adopt such a position and argue for it. I really hope this is not the reason.
Given that Relativity is something that has to be taken into consideration when engineering satellites, it seems to me that arguing against it is just arguing against reality. Doesn’t really matter how cleverly your argument is constructed if it just doesn’t work.
This is a common misunderstanding of what is occurring, and misses a few critical points.
The changing field that drives a particle forward can trivially be made to produce a drive that is travelling faster than light. This does not violate relativity. It is like a light chaser effect. No information is travelling faster than light, so relativity is not violated.
Imagine a proton in an accelerator. We can use a simple electrostatic acceleration system. This a long pipe with a set of plates set a intervals down the pipe. The plates have a small hole in the middle, it is through these holes the proton will travel. We attach high voltage drivers to each plate, each driven by an oscillator. We set the oscillator frequencies and relative phases so that the following occurs.
The plates first are driven with a negative voltage. The proton is of course attracted to the first plate. We set the frequency so that the voltage on the plate has dropped to zero as the proton reaches the plate, and then swings negative as the proton passes - thus repelling the proton down the pipe.
We set the frequency of the second plate’s oscillator similarly, however since the proton is now moving faster, the oscillator needs to be running a bit faster. And we do this all the way down the pipe, for an arbitrarily long pipe. Each oscillator is an individual entity, we only need to synchronise them once and let the system run.
Now if you look at the electrostatic field all the way down the pipe, you see a field that looks like a wave travelling faster and faster down the pipe. The proton rides that wave. There is nothing that says that that value wave can’t travel faster than the speed of light. It isn’t a thing itself it is just a set of values in a field. Just like lights in a light chaser effect, there is no actual movement of an object, just changes in local state.
So in principle, if there is no relativistic effect, the proton should be able to ride the ever increasing wave speed as fast as that wave can take it. But it can’t. Moreover if we try, we observe that the proton does accelerate, but in a manner that exactly fits the predictions of relativity. It isn’t just that it can’t go faster than light, but the speed we can get it to travel at is exactly as predicted by Einstein. We discover that if we work out the energy input from the electric field and measure how fast the proton really does travel at, it is exactly as predicted by special relativity, not some other number. E = mc^2 works exactly right.
Again, railing against relativity requires you to explain why these measurements are as they are. Don’t just dismiss the experiment, come up with your predictions as to what happens, and provide equations that match reality. You need to predict the exact speeds a particle is observed to travel at, given the parameters of the accelerator. Einstein can, so if you believe he is wrong, you need to be able to at least as well. Otherwise you have nothing.
Frances et al, mangling the English language to suit your ends will not wash. You say no information is travelling faster than light, yet you say :-
“The changing field that drives a particle forward can trivially be made to produce a drive that is travelling faster than light. This does not violate relativity. It is like a light chaser effect. No information is travelling faster than light, so relativity is not violated.”
So the particle arrives at the target in the PA before a beam of light would (travelling a similar path) but because no information is transmitted it does not violate relativity. Of course information is transmitted. The arrival of the particle at the detector (or target or whatever) IS the information. Is the particle there or is it not there? - that is information.
Then you contradict yourself by saying that the proton does not travel faster than light…
Tom Hiollings
You misunderstood how the accelerator works. The oscillator is not triggered by the particle, it is free running. It has been programmed to run long before the particle is ever set in motion.