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

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. - Marco Ocram

Marco has made a good observation here, but unfortunately he comes to the wrong conclusion that clocks cannot physically slow down due to relativity. Let's consider a triplet version of the twin's paradox. A stay at home. B takes off in one direction at +0.8c and C takes off simultaneously in the opposite direction with a velocity of -0.6c. After they have travelled for 50 years Earth time they both turn around and return home and B and C arrive back at Earth after a total of 100 Earth years. A who stayed at home is biologically 100 years old and on his death bed but lives just long to say hi to his his returning siblings B and C who are 60 years old and 80 years old respectively. When B took off he considered A to aging 60% slower than himself and C considers A to aging 80% slower than himself, but as Marco points out A cannot be aging at two different rates. Marco is also correct that the motion of B and C cannot make him physically age at a different rate. What he does not realise is that By changing their velocities B and C are changing their aging rates and they are aware of a change because they experience proper acceleration when the took off. Their assumption that A is aging slower than themselves is in fact incorrect as is established when they return. A was in fact ageing faster than both B and C and it was B and C that were in fact aging slower. B can look at his velocity relative to A and not that his elapsed proper time for the journey is completly consistent with him moving at 0.8c and aging 60$ slower than A at all times during his journey and B will find his age is consistent with himself travelling at 0.6c and aging 80% slower than A at every moment during his journey. When they all meet at the end, everything is consistent with the travelling changing their velocities and them being the ones that have their clock/aging rate slowed down. The naïve interpretation that the time dilation effect is symmetrical arrives at the wrong conclusion that they should all age by the same amount. In the twin's paradox, the correct conclusion that the twin's have aged by different amounts when the re-unite is a clear proof that the clock/aging rates must physically change when objects change velocity. To measure their change in velocity and change in clock rate, it is sufficient to measure their own proper acceleration.

I find it hard to understand how complex mechanical/biological clocks slow down when moving.

Here is an example of a mechanical clock that does not rely on bouncing photons to demonstrate time dilation:

Imagine we have an efficient flywheel that has no resistance and maintains its rotation rate of one rotation per second, over very long periods of time. By having a counter that increments by one each time a marker on the edge of the flywheel passes the counter, the number indicated on the counter is the number of seconds that have passed since we reset the counter to zero. We have in effect a primitive clock.

Its moment of inertia is described by $I = 1/2 m r^2$, where m is the mass of the flywheel. Using the concept of relativistic mass (unfashionable but useful sometimes) the relativistic moment of inertia is $I = 1/2 \gamma m r^2$, where $\gamma$ is the usual relativistic gamma factor of $1/\sqrt{1-v^2/c^2}$. When the flywheel is moving relative to us, its moment of inertia increases and its angular velocity decreases in order to conserve angular momentum. To an observer co-moving with the flywheel, the flywheel still appears to rotate once per second, but to us who see the flywheel moving linearly relative to us, the flywheel clock is rotating (or ticking) slower.

If the flywheel is onboard a rocket and there is also a light clock onboard the rocket, they will appear to tick at the same rate. In fact every physical process imaginable (including chemical reaction based) will tick at the same slowed rate according to the external observer. If this was not the case, it would possible to determine absolute velocity by comparing how different types of clocks tick.

Here is another demonstration of time dilation without directly relying on a light clock. It is known that short-lived muons created at the top of our atmosphere by cosmic rays, arrive at sea level event though their the travel time is shorted than their natural lifetimes. Obviously, for this to occur, there must be something slowing down the natural decay time of the muons and this is a real life observation.

We can put the muon example in human aging terms. Imagine a space traveler happens to be born on board a rocket as it passing the Earth at a relative velocity of 0.9797959c and a gamma factor of 5. As the rocket passes a galaxy that 250 light years away from Earth, our traveller is about 50 years old. Without biological time dilation our traveller should have been dead long before passing the distant galaxy. This scenario differs from the classical twin's paradox because the rocket was always moving inertially during the lifetime of the traveller. There is no turn around or acceleration involved, so that removes acceleration as explanation for the twin's paradox, because biological time dilation is present without any acceleration in this example.

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The problem with most of the answers given to this question, is that they imply proper time always ticks at a rate of one second per second and that time dilation is some sort of illusion and nothing physically ticks at different rates due to relative velocities. This point of view, fails to explain why an observer that leaves a given location and returns to the same location will have physically aged less than the observer that remained at the given location. This is an undeniable prediction of SR and and while we have not actually compared ageing of biological entities, we have compared the the elapsed proper time of clocks moving relative to each other and they are different. See the Hafele-Keating experiment.

It is generally acknowledged that predictions of Lorentz Ether Theory (LET) are mathematically identical to the predictions of SR, even by the detractors of LET. Therefore if we analyse the twins' paradox in terms of LET, any conclusions will be in agreement with what SR predicts. It turns out that it does not matter which reference frame we choose to be the one that is at rest with the Ether, the results turn out the same. Lets say we arbitrarily choose the Earth to be at rest with the Ether. When one observer moves away from the Earth, he is moving relative to the Ether and his clocks/biological ageing slow down relative to the observer that remains at rest with the Earth and when the traveling twin returns to the Earth he will be physically younger than the stay at home twin. Lets say the Earth happens to moving at -0.8c relative to the Ether. When the travelling twin accelerates to +0.8c relative to the Earth, he comes to rest with the Ether. The stay at home twin is now aging slower than the 'travelling' twin. However, in order to return home the travelling twin has to turn around and travel faster than -0.8c in order to catch up with the Earth that has a head start. It turns out that because the travelling twin is travelling faster relative to the Ether on the return trip, overall he ages less than the Earth twin when they reunite.

In LET, clocks and all physical processes physically slow down by a factor of $\sqrt{1-v^2/c^2}$ where v is the velocity relative to the Ether. The end result is in exact agreement with the prediction of SR where time dilation is considered to be due to relative motion of observers, but the physical intuition is lost in SR and time dilation appears to be an illusion. Fact is, one twin really will age slower in the twin's paradox and the stay at home twin will be physically older biologically. If both twins live for the same proper time, the stay at home twin might well be dead, by the time the travelling twin returns.

Answer 6

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 7

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 8

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.