The subject of this post is off topic by a lot, but it’s interesting enough for a few comments. I’m a physician, not a physicist, so please check my presentation for accuracy. From the perspective of a photon, the concept of time as we experience it effectively ceases to exist. This phenomenon is a direct consequence of Albert Einstein’s Special Theory of Relativity, specifically the principle of time dilation.
To understand why, we have to look at how time changes as an object moves faster. As an object with mass approaches the speed of light (c), time slows down relative to a stationary observer. This isn’t just a mechanical error in clocks; it is a fundamental stretching of the fabric of spacetime. The formula for time dilation is:
In this equation, as the velocity (v) gets closer and closer to c, the denominator approaches zero, causing the time interval (t’) to stretch toward infinity. At least that’s the inference, as dividing by zero is meaningless in all but a few very unusual forms of mathematics beyond my ken.
The time interval measured by an observer who is at rest relative to the event being timed is t. If you are on a spaceship traveling at 90% the speed of light and you check your watch, you are measuring t. To you, time feels perfectly normal; one second still feels like one second.
The time measured by an observer who is moving relative to the event is t’. If you are standing on Earth watching that spaceship zoom past, you use t’ to describe the spaceship’s clock. Because of the high velocity, you will see the traveler’s clock ticking much more slowly than your own.
Because a photon travels exactly at the speed of light, the math leads to a mathematical singularity. For a photon, the time measured by its own hypothetical clock is zero. If a photon were “conscious,” it would experience being emitted and being absorbed at the same instant, regardless of whether it traveled across a room or across billions of light-years of intergalactic space. Similarly, the dimension of space in the direction of travel contracts to zero. To a photon, the distance between its starting point and its destination does not exist; they are effectively in the same place. I’m stretching things a bit, as the above equation is for objects that have mass, and a photon does not.
While time doesn’t “pass” for the photon, it obviously passes for us. When we look at a star that is 100 light-years away, we are seeing photons that have been traveling for 100 years according to our clocks. The photon travels a distance of zero and a time of zero, while the observer measures a journey of trillions of miles and an entire century. Both perspectives are mathematically correct within their own frames of reference. Anything with rest mass (like a human, a grain of sand, or an electron) requires an infinite amount of energy to reach the speed of light. Because photons are massless, they are required by the laws of physics to travel at c, and only c, in a vacuum.
The above is an example of why Richard Feynman said the universe is not only stranger than you think; it’s stranger than you can imagine. I haven’t touched on quantum mechanics mainly because I know so little about the subject. Feynman also said that if you think you understand quantum mechanics, you don’t understand quantum mechanics.
The point I’m trying to make, is that the deeper one goes into the basic nature of the universe, the more complex nature becomes, and the greater the difficulty in understanding it is. We may soon reach a point where our brains are unable to understand the core concepts of reality, just as a dog cannot understand long division.
The new thinking machines we are building may understand all of nature. Whether they will tell us or whether we’ll understand what they reveal if they do tell us is uncertain. As I said above, beware of physics presented by a physician.
