Relativistic time dilation and the biological process of aging

Question

Although I understand many of the "thought experiments" which demonstrate how simple clocks slow down (when moving) as result of the constancy of light speed postulate, I find it hard to understand how complex mechanical/biological clocks slow down when moving. I mean, I understand the famous example of photon bouncing between two mirrors that move perpendiculary to the relative position vector of the mirrors, but real daily clocks do not involve photons (which are particles of light, so the basic postulate of special relativity obviously influences them).

Therefore, I proposed to myself the following argument: biological aging processes are all a result of chemical processes in the cells, which ultimately depend upon electromagnetic fields between atoms and electrons. Therefore, since electromagntic interaction are mediated by either photon or "virtual photons", one can get an explanation of the slowing of aging processes based on the following assumptions:

• Photons obey special relativity; in particular, they experience time dilation.
• Virtual photons obey special relativity; in particular, they experience time dilation.

The first assumption is obviously correct, since photons are quatized electromagnetic waves, but I'm not sure of the second assumption - virtual photons is an advanced concept in physics which I had not studied yet.

So is my proposal correct? and if not, how does slowing down of complex clocks arises from primitive clocks?

Answer 1

I think you misunderstand time dilation. It doesn't mean that clocks slow down. It means that the time between two events is frame dependent. Specifically, the time between two events in a frame where they occur in the same place is less than the time between the same two events in any frame in which they occur in different places. It is the time interval that differs between frames- not the ticking of the clocks. If the interval is 5 seconds in one frame and 4 seconds in another, then clocks in the two frames will record different durations not because one clock has slowed down or the others speeded up, but because the actual duration is different.

On Earth your heart might be beating once a second, say. In the frame of a passing muon, your heart beat might be measured as lasting a minute. In some other frames, your heart beat might last 30 seconds, or an hour, or 9.23 seconds, or any other interval you care to mention, depending on the speed of the other frame relative to you. There is no physical effect making your heart beat at a different rate- and indeed, if you thought there was a physical effect, how could you explain how your heart could be effected to beat at any number of different rates at the same time? The fact is that an interval of a second between two events here on Earth can be an interval of any multiple (greater than 1) of a second in any other frame. The effect is due to the geometry of spacetime, and has nothing to do with the working of clocks.

Answer 2

Special Relativity (SR) is now best thought of as giving us 'new' concepts of space and time. For example if two events are separated spatially by distance $\Delta r$ and in time by $\Delta t$ in one inertial reference frame, then the 'interval', $(\Delta r)^2 - c^2(\Delta t)^2$, will have the same value even if $\Delta r$ and $\Delta t$ are both measured in a different inertial frame.

$c$ can be thought of as a constant with the dimensions of speed, that enables us to express times in units of distance. It is easily shown that $c$ is the highest speed at which a particle can travel – a fundamental limiting speed. It is also the speed at which light travels in a vacuum. In the early years of Special Relativity, and for long after in popular presentations, great emphasis was placed on $c$ in the equations of SR being the speed of light, and the behaviour of light signals was considered part of the essence of Special Relativity. In my opinion this is no longer the case; the aspects I've emboldened above have assumed over-riding importance.

For this reason, I'm afraid I'm unsympathetic to photon explanations for relativistic effects. You say "I find it hard to understand how complex mechanical/biological clocks slow down when moving." This makes it seem as if we should look 'inside' the clock for an explanation. A more careful description of the time dilation phenomenon is that the time interval ($\tau$, say) between two events as read by a clock that travels at constant speed between the two events, and in whose frame of reference the events occur in the same place, is shorter than the time interval ($\Delta t_1$, say) between the events as calculated from the readings of synchronised clocks present at both events and at rest in a frame in which the events are spatially separated (by $\Delta r_1$, say). The phenomenon arises from the nature of time and space, in particular the constancy of the interval, $(\Delta r)^2 - c^2(\Delta t)^2$ as found from $r$ and $t$ measurement-pairs made in different inertial frames. [Specifically, $0^2-c^2 \tau^2=(\Delta r_1)^2-c^2 (\Delta t_1)^2$, so $\tau^2<(\Delta t_1)^2$.]

Answer 3

Time doesn’t slow down for our biological space travelers. Everything from cesium transitions to disease progression proceeds normally. It’s only our so called stationary clocks that measure the time to move slower.

Note that the existence of a reference frame that sees your clock ticking slowly has no affect on your clock, or your biology.

Answer 4

Time dilation results when a clock at rest in its own frame A is compared to a row of syncronized clocks in another frame B, that moves in relation to A. So the effect doesn't compare for example the pulse rate of 2 people in different frames. Note that one of the clocks of B shows the same effect if compares itself to a row of synchronized clocks of frame A. The effect is symmetric.

However, if the first clock accelerates for a while until becoming at rest somewhere in the frame B, its recorded time interval is smaller than what can be seen in B. And a communication with any point of frame B will confirm that. The effect is no longer symmetric.

So, acceleration is required to "the trip to the future" of another frame in SR. It cannot be explained by thinking only of relative velocities.

Answer 5

I go with a different explanation. The theory of relativity tells us two things: 1) we can use any inertial frame to describe the physics 2) and all are equivalent.

From 2) we can derive the Lorentz transformations, and go to different frames; some of them more convenient then others. You know the story (a lot of other answers focus on that).

But lets not forget 1). The premise is, you can describe physics with the known/updated physical laws in any reference frame of your choosing. You, in your question choose the reference frame of you beeing stationary (which is great; no nitpicking about earth circular motion please. It is good enough as a stationary frame.)

So from this frame we need to be able to understand time dilation. Which is what the light clock thought experiment does. It basically (if you also look at Maxwells equations) tells you that Electrodynamic processes run slower for moving 'contraptions'. If you accept that, you are almost done:

So what is biological ageing? It is based on the time for chemical reactions. What are chemical reactions? Electrodynamical processes, which we know to run slower, if in movement.

Answer 6

You shouldn't include virtual photons in your reasoning, because they are basically a mathematical trick to describe interactions between real particles in a perturbation series. As "virtual" particles they can indeed be off-shell, i.e. do not obey the relativistic energy-momentum relation E=pc and could be said to be "faster or slower than light" (or even go backwards in time). But the interactions between real particles still obey the rules of special relativity (in fact this is build in as a postulate in quantum field theory).

Furthermore, special relativity doesn't only say that photons travel at the speed of light, but that all massless particles do and that all massive particles travel at speed below that of light. So there is just no way that interactions, and with that: information, can travel faster than light. When we see, from our frame of reference, a light-clock in another frame of reference running slower, all interactions have to be slower, too, when seen from our frame of reference.

Answer 7

I'd like to think of this from the viewpoint of time resulting from an increase in entropy. Not quite an established and proved theory, it does provide some sort of framework for this question of relative time in relation with biological processes.

Since many biological interactions on the atomic scale result from entropy, e.g. neurons firing as a result of ions equalizing an imbalance in charge and concentration, an increased velocity of an object could be seen as resulting in a slower increase in entropy, compared to the observer.

I have more trouble connecting this to the concept of virtual photons, I'll leave that to someone else to cover.