gib65 Posted October 6, 2007 Share Posted October 6, 2007 I'm thinking of the fact that time dilates to a halt relative to an observer at rest as you approach the speed of light. That means that no time passes for those inside the space ship that's traveling at the speed of light. All their displacement in spacetime is through space. As the space ship slows to a halt, no displacement in space occurs but displacement in time dilates to its usual rest rate (relative to an observer also at rest, of course). But what is this "usual rate"? Wouldn't it just be the same rate of displacement as that through space which the spaceship traveled when going at the speed of light? That is, when at rest, do we travel through time at the speed of light? I might be getting my terms mixed up, but isn't this what Lorentz invariance is all about? Basically, the question is: Do we pass through time at the speed of light? Link to comment Share on other sites More sharing options...
iNow Posted October 6, 2007 Share Posted October 6, 2007 Basically, the question is: Do we pass through time at the speed of light? How would you calculate speed without the notion of time having already been invoked? Link to comment Share on other sites More sharing options...
timo Posted October 6, 2007 Share Posted October 6, 2007 I'm thinking of the fact that time dilates to a halt relative to an observer at rest as you approach the speed of light. That means that no time passes for those inside the space ship that's traveling at the speed of light. And since you cannot have a spaceship travelling at the speed of light, that statement is pointless. All their displacement in spacetime is through space. Nope. As the space ship slows to a halt, no displacement in space occurs but displacement in time dilates to its usual rest rate (relative to an observer also at rest, of course). Strange wording, but I think what you meant is correct. But what is this "usual rate"? The rate of your rest frame, just as you defined it in your previous sentence, meaning the time measured in the ship equals that of your rest frame. Wouldn't it just be the same rate of displacement as that through space which the spaceship traveled when going at the speed of light? ? That is, when at rest, do we travel through time at the speed of light? ?? You mean speed as in "meters per second"? I might be getting my terms mixed up, ... Possibly. ... but isn't this what Lorentz invariance is all about? There is something similar to what you seem to be talking about: For mathematical reasons, the "velocity" (the term is highlighted with "" to emphasize that it's not the canonic meaning of velocity") through spacetime is undetermined by a real factor f. What we do is scaling the velocities such that the norm we use on the velocity vectors equals 1. Well, maybe it's c in case you don't use a system where c=1; I don't know for sure (I always use c=1 and plug in c's afterwards, if needed). So (almost) all velocities have a norm of 1. The funny thing is, that there is one exception to that rule, namely the velocity of light-like objects. The norm of all their possible "velocities" is zero, so it's not possible rescaling them to 1 (no number times zero equals one). This is in fact the reason (or a symptom of - probably depends on point of view) why there is no rest-frame for light, why you can't reach the speed of light, ... Basically, the question is: Do we pass through time at the speed of light? Depends, see above. Link to comment Share on other sites More sharing options...
Osiris Posted October 6, 2007 Share Posted October 6, 2007 I'm thinking of the fact that time dilates to a halt relative to an observer at rest as you approach the speed of light. That means that no time passes for those inside the space ship that's traveling at the speed of light. All their displacement in spacetime is through space. As the space ship slows to a halt, no displacement in space occurs but displacement in time dilates to its usual rest rate (relative to an observer also at rest, of course). But what is this "usual rate"? Wouldn't it just be the same rate of displacement as that through space which the spaceship traveled when going at the speed of light? That is, when at rest, do we travel through time at the speed of light? I might be getting my terms mixed up, but isn't this what Lorentz invariance is all about? Basically, the question is: Do we pass through time at the speed of light? Yes... everything is traveling at the 'speed of light'. If the spaceship were traveling c/2... then the other half of c would be used to move through time. Link to comment Share on other sites More sharing options...
Spyman Posted October 9, 2007 Share Posted October 9, 2007 Basically, the question is: Do we pass through time at the speed of light? According to Prof. Mark Morris: Relativity also posits that everything from planets to people moves at a total of the speed of light when one adds up all movement in the four dimensions of space-time. You and I are moving at the speed of light through time … just by virtue of sitting still. http://www.dailybruin.ucla.edu/news/2005/apr/22/changing-the-physics-of-philos/ Link to comment Share on other sites More sharing options...
gib65 Posted October 9, 2007 Author Share Posted October 9, 2007 Thanks to the last two replies. They show a good understanding of my question and answer it accordingly. Sorry to the first two replies; I could have used better terms and ideas. Link to comment Share on other sites More sharing options...
swansont Posted October 9, 2007 Share Posted October 9, 2007 To expand on the Prof Morris quote — The four-vector for velocity is an invariant. So if you are at rest, that vector has the entire length along the time axis, and that length is always c. Link to comment Share on other sites More sharing options...
Severian Posted October 19, 2007 Share Posted October 19, 2007 The speed of time is constant and equal to 1. I can prove this mathematically: [math]\frac{\partial t}{\partial t} = 1[/math] Link to comment Share on other sites More sharing options...
asprung Posted April 6, 2008 Share Posted April 6, 2008 What would seem constant is the passage of the present- "now"- into the future becoming the past. It seems that time can be diffrent for diffrent observers during this canstant passage. The speed of "now" must be at least the speed of light so that light does not run ahead into the future. Link to comment Share on other sites More sharing options...
thedarkshade Posted April 6, 2008 Share Posted April 6, 2008 Do we pass through time at the speed of light?In that case we wouldn't really pass through time AT ALL! Link to comment Share on other sites More sharing options...
iNow Posted April 6, 2008 Share Posted April 6, 2008 The OP doesn't really make sense. It's like asking if the direction left passes at the speed of light. Link to comment Share on other sites More sharing options...
gib65 Posted April 7, 2008 Author Share Posted April 7, 2008 The OP doesn't really make sense. It's like asking if the direction left passes at the speed of light. I'm sorry, iNow, I knew my question was a difficult one to ask even when I was writing it. Maybe this will help: the direction left doesn't "pass" in any meaningful sense, but time does. Link to comment Share on other sites More sharing options...
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