In the summer of 1996 I had a lot of time to think about things. I was a Unix engineer in
What is time? Really, what is it? It is nothing more than a unit of measure for the decay of a cesium atom. We know that the rate of decay of a particular cesium isotope is so stable and dependable that we use that decay as our standard for the unit of measure of time. What are we measuring? We measure age. The age of the Universe, our own age, the age of the earth. We measure the total rate of all physical and chemical interactions since the beginning of the Universe. We know that this interaction or this chemical reaction occurred before this other one. We measure the difference between those interactions in space. In reality, there is no such thing as time. It is not something tangible, just like an inch is not tangible. An inch of something is something, but it is not an inch, it is a measurement of something. Time is not tangible, it is a measure of the rate of decay and chemical reactions that occur throughout the universe. Mostly, we think of time in terms of the chemical reactions that cause us to age. To humans, the desire to go back and undo something is so strong, that we have created an idea that time is tangible and can be manipulated. You can not manipulate something that does not exist. Can you reverse the order of all chemical reactions in the universe to "go back in time?" No. Can you just cool off a cake and turn it back into eggs, flour, milk, and sugar? No.
How does this relate to Relativity? The person traveling near the speed of light AGES very little compared to someone not traveling at the speed of light. Do they travel through time? No. Time does not exist. So what happens? The chemical reactions that we call AGING appear to happen slower to people traveling near the speed of light from the frame of reference of Earth. Conversely, AGING appears to happen more rapidly to people on earth from the frame of reference of the people traveling near the speed of light. To each group AGING appears to happen at the normal rate within their frame of reference. So, the person traveling near the speed of light thinks a year has gone by. The person on earth thinks ten years have gone by. Why does traveling near the speed of light appear to slow down aging when viewed from the frame of reference of earth?
Time does not exist, it is only a measure of what we call aging. Aging is essentially the sequential series of organic chemical reactions that take us from conception to death. Why would these CHEMICAL reactions appear to slow down near the speed of light from the perspective of someone standing on earth?
What slows these things down? Removing thermal energy will certainly slow these chemical reactions down. When we reach zero degrees Kelvin, that is pretty much an all stop except for external kinetic interactions and quantum effects. More than likely, this is not what happens.
So what changes when we travel faster and faster? Well, Mass changes. Mass is a measure of an object's resistance to a change in velocity or direction. As an object moves faster, it's mass increases because it then takes more energy to make it go faster, or it takes a more energy to make it change direction than when it is just sitting still.
If nothing else changes, then why would a increase in mass cause chemical reactions to slow down? We don't necessarily see that on earth. As the speed of an object increases to the speed of light, mass increases exponentially to infinity. What changes as mass increases? Gravity for one. The gravitational field increases as mass increases. Could gravity cause chemical reactions to slow down? Not in conventional physics. Gravity is the weakest force in conventional physics. It's influence at the molecular or quantum level could be considered negligible compared to the strong and weak nuclear forces. Or can it? As the gravitational field increases exponentially in intensity as mass increases, and if gravity has a much stronger effect at the quantum level than previously known, then it is possible that the strengthening gravitational field could actually have a slowing down effect on all quantum motion and interaction. Essentially, gravity could put everything into slow motion, from the perspective of someone on earth. But from the point of view of the person traveling at the speed of light, they see everything occurring as normal around them, but everything happening much faster on earth.
This would mean that even light would change speed when passing through intense gravitational fields, from the perspective of someone looking at it from earth. It also means that gravity can affect quantum motions and interactions.