But due to their extremely high speeds, time slows down for them, and their lifespans extend hundreds of times longer than if they were at rest. Physicists can see the direct effect of the time dilation in the markedly higher number of particles that make it to the detectors than would be possible with their resting lifespans—because the detectors are sometimes about a half mile away from the accelerator ring where the particles are created, and, even at close to light speed, it would take the particles much longer than their incredibly brief natural lifespans to reach the detector, and almost all would “die” and disappear along the way. But their very high speed slows down their relative time and stretches out their lifespans, so that in reality, most of them make it all the way to the detectors.
. But as seen by the cop parked on the roadside, the light from the flash travels quite a bit farther, as you can see from , because the front of the bus would have moved forward during the time the light is in transit. Now, here’s the crux of the argument: If the speed of light is the same for both you and the cop, but the distance traveled is different, then it must be that the time of travel of the light is also different for you and the cop. To fully appreciate the point, imagine the strobe light is synchronized with a clock at the back of the bus to flash every two seconds—then your perception of two seconds sitting inside the bus, and hence the lapse of time measured by the strobe light, would be different from that of the cop looking at those same light flashes. Thus, insisting that the speed of light is the same for all observers regardless of their individual state of motion immediately leads to the unavoidable conclusion that the measure of time must be different for people moving relative to each other.
of what could be a typical timeline of memorable events over a two-year period between the ages of sixteen and eighteen years, and I compare it with a similar timeline for another two-year period later on in life between the ages of forty-seven and forty-nine years. The intervals between those memorable events act as our true yardstick or “unit” for the measure of time, because they are the ones that really mark our recollection of the passage of time. The two years between sixteen and eighteen are packed with events that stay with us, making the time “unit” smaller, so that we pass through several such “units” of time, and in our memories, it feels like that two-year period lasted forever. On the other hand, between forty-seven and forty-nine, only a couple of time “units” have come to pass, so these last two years seem to have just flown by in comparison.
Our experience of time is indeed relative and varies with age, sort of like how the passage of time varies with the speed in the theory of relativity. In relativity, as the speed increases, the unit of time seems to get stretched out compared to someone at rest, while in life, our perceived unit of time also gets stretched out as we get older compared to someone in their youth. After a couple of years of separation, a young man might say to his aging uncle, “Hey, long time no see!” and the old man might very well respond, “Really, has it been that long?” Well, that sounds a lot like what the twins in the twin paradox might say to each other after the trip to the stars.
Life is not being quite as objective as science, so one could take quite the opposite perspective, that time seems to go by quicker when we are having fun. Since we seem to have much more fun when we are young, shouldn’t time seem to go slower when we are older and weighed down with responsibilities, and it is not so much fun anymore? There is some truth in that, and it is just another way to see how our experience of time is indeed relative. But this does not contradict what was said before: Sure, several days of vacation can seem to zip by much faster than a single hour waiting in line at the Department of Motor Vehicles (DMV), but that is only our perception of time as we experience it at the moment, which is quite different from how we recollect different periods of our lives and how they register in our memory. When we experience fun things, it might seem like time went by too fast because we wish they could have lasted longer, but when we remember those fun times, they do seem to stretch out because we remember so much about them. On the other hand, the hours we spent just waiting in lines or doing dull, routine things might have seemed never-ending at the time, but they just fade away quickly from our minds as if they had never happened.
A microsecond is one millionth of a second, and a nanosecond is one billionth of a second. So, for a particle that exists for one microsecond, one second is equivalent to a million times its natural lifespan.