Riding a Beam of Light & Travelling At The Speed Of Light
Ever wonder just what it would be like to ride on a beam of light? Put another way, have you ever wondered what it would be like to travel at the speed of light? We can demonstrate by means of an experiment, using a clock set into motion, and watching it tic as it moves. By moving it fast enough, we will be able to watch it as we might watch light itself, move across space. By seeing what happens to the clock, we see exactly what would happen to us, were we to make such a journey ourselves.
Let us begin by imagining ourselves on a space station with a rocket-powered clock, a very large clock that can be read from very, very far away, by using an extremely powerful telescope on the station. The clock is equipped with a second hand we are able to see through our telescope, at any distance, allowing us to watch time pass, as the clock moves. We send the clock far out into space, the precise distance of exactly ten light minutes from the station. We program its rockets to turn it around, aim it right for the station, accelerate it to nearly the speed of light very quickly, allow it to coast at that speed for a while, then decelerate it just as quickly, finally bringing it to a halt at the very moment before it would crash into our station (thus preserving the experiment by not annihilating clock, station, and observers). Looking through our telescope, we watch the clock turn around, once it is ten light minutes out. It starts heading straight for us. We watch it as it approaches. What, precisely, do we see?
First, for nearly thirty seconds, we see the second hand on the clock gradually move more and more slowly, almost stopping completely for what is only a second to us. In that second, the clock grows very, very fast. Then, for nearly thirty more seconds, we see the second hand on the clock move gradually faster. The clock comes to a halt right in front of us, the second hand moving at the proper speed. A minute and a second have elapsed. The clock sitting in front of us though, shows that less than a minute has passed for it, even though slightly more than a full minute has passed on our clock at the station since the very first moment we began seeing the clock approach.
The clock has traveled ten light minutes. We, however, watched it travel for only a minute, plus one second. Its clock shows that less time has passed for it, than for us. Considering its distance from the station (ten light minutes), the clock should have spent more than ten minutes traveling, since, traveling slower than the speed of light, it had to take, from our perspective, minimally, ten minutes to arrive, plus an additional minute for accelerating and decelerating – assigning thirty seconds to each. This is approximately an eleven-minute journey. Why did we see it for only a minute and one second, when it had to take, approximately (according to our measures), eleven minutes to arrive at the station? Why doesn’t its clock reflect the approximate eleven minutes of its journey?
Relativity, of course, explains why. While traveling at 'nearly' the speed of light, time 'nearly' stands still, so appropriately, its second hand barely moved. For the single second that the second hand nearly stopped and the clock grew in size, it was traveling at nearly the speed of light. Relativity tells us that, in our frame of reference, time nearly stood still for the clock while it was moving at that speed. And indeed, we watched the second hand nearly stand still, while the size of the clock grew ENORMOUSLY, as the second elapsed, indicating how much closer it came and so just how far it had traveled in that second. Before that, we saw it accelerate to near-light speed as we watched the second hand gradually slow down. After, we watched it decelerate, as the second hand gradually sped up again. We watched it cross the majority of the ten light minutes of space in what appears to us (according to what we saw through our telescope – our measures), to be the single second that the hand on the clock nearly stopped moving altogether, and the clock grew so much in size. Staying close behind the approaching edge of its own light, we see the nearly ten minutes that it spent traveling at near-light speed, over the course of just a single second. What we do not see is a clock nearly frozen in time for ten minutes. Ten minutes of its journey look like only a second to us, because at the moment we watched the clock turn around, it had already completed most of its journey, even though we did not see it until later.
When we saw the second hand start to slow down, the clock had already traveled nearly ten minutes along its path. The stream of light we saw during the course of the minute and the second that we watched the clock travel was a record of this journey. It is what happened according to the clock’s measures for time and space. Relativity tells us that what happened according to its measures for time and space is not what happened according to ourmeasures for them. According to our measures, a journey was made across a vast distance of space and time, according to our stipulated measures. According to us, millions of miles of space were crossed, and many (eleven) minutes were spent doing so. But, according to its measures a much shorter distance was crossed, and most importantly, fewer minutes and so less time passed during its journey.
Now, let us imagine that, instead of spending the two, thirty-second periods of time required to accelerate and decelerate the clock, we accelerate it to nearly the speed of light instantaneously – and likewise decelerate it instantaneously. This would reduce both thirty-second periods to zero seconds, as instantaneous anything means that no time whatsoever is spent. Were we to completely eliminate this minute spent for accelerating and decelerating, what would we see then? We can imagine what we would see, were no time spent for accelerating or decelerating, by editing our record of that minute and one second of light we observed, while watching the clock’s near light-speed journey through the telescope. We do so by deleting the first thirty seconds of its acceleration, as well as the last thirty seconds of its deceleration, since we are imagining that neither requires any time. This would leave only the second in between, when the second hand on the clock seemed to stop, and the clock grew so much. In other words, we would get exactly a second's worth of light, and no more.
We would see the tiny image of the clock (starting from its turnaround point) grow enormously in the passing of a second, appearing before us once the second passed. We know that, had it gone at the exact speed of light, not just nearly that speed, then instead of a second passing, no time at all would have passed; zero time, to be precise. There would not even have been time for the rocketing clock to brake, to decelerate. Looking through our telescope we would have seen nothing revealing a journey “before,” it would have appeared before us, from one moment to the next. Its journey would be completely unknown to us, until the very moment it arrived. Relativity tells us that this is what would happen to the clock, making the entire journey at light speed.
According to relativity, time stands still at the speed of light. Moving at that speed, the second hand on the clock would not have advanced, in the least. This means that the time spent for its journey would be reduced to zero, which is to say, reduced to an infinitely small moment. The clock would be a moment of light, or a "particle" of light, which, by any other name, is a 'photon.' Since, for the sake of our explanation, the clock and a photon are one and the same, we can say that the clock is accurate for determining how much time elapses on a photon. No time passes on the clock, traveling at uniform light speed, which means that no time passes during a photon’s journey, either. Not only that, with respect to its measure of spatial distance.
A photon is at one place and one place only, since it is 'there' for only a single moment. There is never any 'time' for it to move (or brake), since a zero-dimensional moment provides none. (This is consistent with relativity, as the enormous distance of its journey, is 'contracted' infinitely, reducing this distance to zero.) According to the clock’s measures traveling at the speed of light, and so, for any photon too , the moment it is at what is, according to our measures (of space ad time), one end of its journey, is, for it, the same moment that it is at, what is, again according to our measures , the other end. Put another way, in the universe of photons (the extent of its measures) there is no 'then' or 'there', only 'here' and 'now', with no "elsewhere" or any "other" moment except the present one.
According to our measures, each end of its journey is two different places, at two different moments in time, while according to its measures , it is not at two different places, but at a single one, making both ends of its journey and every point in between (which is, in classic terms, a line) the very same place and the very same moment. For it, that single place and single moment is the entire extent of its existence. Distance, either spatial or temporal, does not exist for the photon. For it, 'there' does not exist, any more than 'before' or 'after' do. Its frame encompasses only 'here' and 'now', and does not extend beyond. It is this little insight that reveals what space really is, a collection of lines, stacked upon each other to form our constantly changing three-dimensional space, in the same way that a collection of lines on a surface could define that surface. Adding time, a ‘stack’ of surfaces results. That is what the visible universe consists of, a collection of lines ordered according to time’s passage, which again, according to relativity, depends wholly upon one’s motion. This tells us what the visible universe and all the space that we see around us really is and most importantly, that what we see is happening right now, not billions of years "ago."
Because an understanding of the principles of relativity is so uncommon, especially among many who teach us, indeed among many who teach us science, we think that because light "takes time" to travel, what we see is not happening when we see it. If we recognize how the photon "particle" is actually instead a line forming part of the space that surrounds us with each passing moment, which is exactly what Einstein did. He recognized that that this common, conventional, and widespread notion of 'now' being when things actually happen in – and this is according to Einstein – never anything more than a mere "stipulation" (the term he used in The Theory of Relativity by Albert Einstein, Appendix V) "that we place upon ... physical existence," unless we mean the one 'made' of all the light that we perceive around and in us. This 'now' is as real and physically existent as much as everything that it reveals is. This is our "true" 'now' present moment, as far as can be seen. Looking far enough we can see the very shape of space and time itself within our universe – that is, within the visible one.