<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>So it means that once your vehicle reach speed of light (let's suppose it's possible), the rest of the ride is free ? (you can't expense energy if you have no time to do so...) <br /> Posted by killium</DIV></p><p>Well, as you are aware you are trying to describe the impossible, what sort of answer do you expect to get? Nothing with any mass can be accelerated to the speed of light. If we just "suppose" it is possible, without modifying the theory that says it is impossible, the results will be nonsensical.</p><p>Unless subject to other forces (like gravity), once you reach <em>any</em> speed you need not expend any more energy to stay at that speed - if you push something in space it keeps on moving. </p><p>Consider this... if you were moving at the speed of light and no time was passing for you or your vehicle, and you could, from your point of view, instantaneously travel to anywhere in the universe, <em>how could you stop when you got there?</em> </p><p> </p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Something about all this just jumped to my eyes: Red-Shift. This is due to photons loosing energy while in transit right ? If a photon experiences no time, how could one (or many) of its caracteristics (like energy level) change ? And how does that change can then be proportionnal to time ? Can someone points me to where i goofed ? lol! <br /> Posted by killium</DIV></p><p>You are assuming that redshift is <em>due</em> to photons losing energy, but have you considered that <strong>both</strong> the redshift and the loss of energy are due to another cause? If you think of the doppler shift of sound as a train approaches and then recedes, the sound itself is not changed in any way during the process - the sound would be normal for a listener that is moving alongside the train. It is the frame of reference of the listener, or the observer, that is changing, not the light or the sound.</p><p>The expansion of the universe is described in cosmology as the <em>change in the scale factor of the background metric</em>. The change in this scale factor during the billions of years between the emission and detection of the light is what can be thought to cause an apparent redshift. It is as if we are moving away from the source of the light which results in a similar effect to the lowering of the frequency of the sound of the train as it recedes from us. The sound itself remains at the same frequency throughout, but that frequency apparently changes depeding on the frame of reference of the listener.</p><p>If you fire a ball-bearing at a target and it leaves the muzzle of the gun at 200mph, but the target is receding at 100mph, the ball-bearing will be moving at 100mph relative to the target when it hits it. But the ball-bearing did not lose that energy... </p> <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>