![]() ![]() Scientists can accelerate subatomic particles to much higher speeds. That can only happen if fast-moving pions experience time more slowly than stationary ones.īy the way, 99.99% the speed of light is not the record for particle accelerators. When scientists create pions traveling at 99.99% the speed of light, they find that they travel about 600 meters (1920 ft) before decaying. But that’s in a Universe in which all clocks tick equally - that is, a stationary human clock and a moving “pion clock” tick at the same rate. If you had a pion and hypothetically accelerated it to the speed of light, which is roughly 300,000 km/sec (186,000 mi/sec), it should travel just over 8 meters (27 feet) before it decayed. This lifetime has been measured to incredible precision. They also are unstable, decaying in 28 × 10 -9 seconds. How does this work? As an example, let’s consider a subatomic particle called a pion. We can use these tiny clocks to examine what happens as we get them to go faster and faster. Furthermore, these particles have their own clock. We can take subatomic particles and accelerate them to very high speeds - speeds very near the speed of light. Scientists have been doing this experiment for decades. ![]() What happens if you take an object with mass and move it faster and faster? How does that object experience time? Approaching the speed of light Very often, the trend you see tells you what will happen when you get to the forbidden value. If you can’t solve a problem exactly for a specific value of some parameter, you can use other values of that parameter and ask what happens as you get closer to the value you want. So, let’s use the approach of limits, often used in calculus class. And if you want to toss some more 9’s in there, go ahead the equations work just fine. On the other hand, while Einstein’s equations don’t apply for 100% the speed of light, there is nothing stopping us from asking the same question for objects traveling at 99.999999% the speed of light. If we can’t do an experiment and our equations don’t apply for the speed of light, are we stuck? Well, to a degree, yes. ![]() Thus, those equations don’t apply for light itself - only for objects traveling slower than light. At the exact speed of light, they break down. Einstein’s time-related equations apply for objects traveling with zero speed up to, but not including, the speed of light. Here, the story gets a little more complicated. The power of limitsĪs we are forbidden from doing the definitive experiment, we must turn to theoretical considerations. Clocks most certainly have mass, so no clock can travel alongside light to allow us to do the experiment. After all, only objects without mass (like photons of light) can travel at the speed of light, and objects with mass must travel slower. The only problem with that idea is that it is completely impossible. We could design an experiment in which a clock is attached to a photon. Physics is an experimental science, and the definitive way to answer questions is to do experiments. But that’s the time we experience. What does light experience?Īnswering this question is a bit tricky. (About eight minutes.) So, it seems rather obvious that light experiences time. After all, we see light pass from the Sun to the Earth. On the face of it, the idea that light doesn’t experience time seems kind of silly. ![]()
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