# What happens biologically during time dilation?

• danielatha4
Relative to the dude's reference frame, time moves more slowly for all events. This includes the replication of cells in the dude's body.

#### danielatha4

If someone is traveling close to the speed of light, relative to your reference frame, then the time observed on their clocks slows. But what does that mean when it comes to aging? Do their cells that make up their body replicate more slowly? Is there any type of disagreement in the amount of cells replicated in their body between your reference frame and theirs?

danielatha4 said:
If someone is traveling close to the speed of light, relative to your reference frame, then the time observed on their clocks slows. But what does that mean when it comes to aging? Do their cells that make up their body replicate more slowly? Is there any type of disagreement in the amount of cells replicated in their body between your reference frame and theirs?

You are thinking about it wrong.

In the frame of reference of the dude moving near c, there is no time distortion effect. There's no experiment he can perform upon himself or anywhere inside his spaceship that will show he's moving near c.

In fact, there is no way you can show that it is not you who is moving. There is no objective frame wherein one of you is not moving. It's all relative (that's why it's called relativity). The dude's frame of reference is exactly as valid as yours - he is stationary, and it is you who are traveling at a near c.

In conclusion, to ask what is happening to his cells is to ask what is happening to your cells.

Well on average it takes a cell to completely replicate anywhere between 12-24 hours. So we’ll use 24 hours for this example, or 86400 seconds.

So let’s use an example where someone is traveling .8c relative to your reference frame, which we’ll assume is an inertial reference frame.

Event 1 we will call the beginning of replication for a cell, and event 2 will be the completion of replication. So in the observing reference frame

t2 – t1 = 86400 seconds.

But the time elapsed observed from your frame for the person traveling .8c is given by

t’2 – t’1 = (t2 – (vx2/c^2))(gamma) – (t1 – (vx1/c^2)(gamma)

We’ll say at t1 the x coordinate will equal 0 and with simple calculations knowing the person is traveling .8c we know that the x coordinate at t2 is 2.07x10^13m

(86400 – ((.8*2.07E13)/2.99E8)(1/.6)) – 0 = 51936.31s

Which only allows about 3/5 of the replication of the same type of cell in the reference frame of the observer. Therefore, for every 5 cells replicated on your body, you only observe 3 replicated on the person traveling .8c with respect to you.

danielatha4 said:
Well on average it takes a cell to completely replicate anywhere between 12-24 hours. So we’ll use 24 hours for this example, or 86400 seconds.

So let’s use an example where someone is traveling .8c relative to your reference frame, which we’ll assume is an inertial reference frame.

Event 1 we will call the beginning of replication for a cell, and event 2 will be the completion of replication. So in the observing reference frame

t2 – t1 = 86400 seconds.

But the time elapsed observed from your frame for the person traveling .8c is given by

t’2 – t’1 = (t2 – (vx2/c^2))(gamma) – (t1 – (vx1/c^2)(gamma)

We’ll say at t1 the x coordinate will equal 0 and with simple calculations knowing the person is traveling .8c we know that the x coordinate at t2 is 2.07x10^13m

(86400 – ((.8*2.07E13)/2.99E8)(1/.6)) – 0 = 51936.31s

Which only allows about 3/5 of the replication of the same type of cell in the reference frame of the observer. Therefore, for every 5 cells replicated on your body, you only observe 3 replicated on the person traveling .8c with respect to you.

You're still on the wrong track.

If you are watching an old film (you know the ones where the camera is cranked by hand, so everyone is running around faster than normal?) would you check to see whether the cars are fast by a factor of X and the people are walking fast by a factor of Y and the clocks are fast by a factor of Z and then check to see if there's a discrepancy between X and Y and Z?

No, if the film is moving fast, then everything, everything is moving fast exactly the same. They're not moving fast individually; you can say that the entire-world-that-is-the-the-film as a single unit is moving fast.

Furthermore, if the people in the film discussed it amongst themselves (if people-on-cellulose could somehow be alive), they would not see any problem with time. The fact that you are observing them at the wrong speed does not meant here's anything wrong with their world.

So:

It is not the individual components in the dude's spaceship that are slowed down. It is all of time in his frame of reference that is slowed down. And even that is only with respect to you.

There is no absolute time against which both you and the dude can have events measured. The passage of time is a property of the frame of reference you or he are in.

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I understand that in the moving person’s reference frame (that is, moving relative to another frame) everything remains the same, as their frame in an inertial reference frame. Just like what is observed in the other person’s inertial reference frame. I’m talking about their observations relative to each other.

There is less of a difference in time between events one and two for someone traveling an appreciable fraction of the speed of light relative to an inertial frame and IN the inertial reference frame that is observing. Is this not right?

I actually think I got my own logic wrong in the last post. If event 1 indicated the beginning of a cell replicating and time 2 indicated the ending of it. Then the cells would replicate faster for the person traveling with respect to the observer, as it took 3/5 the time to finish replicating as in the observer’s frame, and this is of course IN the observer’s reference frame. NOT in the frame of the one traveling. For the one traveling the effects should be reciprocal. However, I know your still arguing against that claim in general.

Are you claiming that the rate of cell replication is modified to compensate for time dilation, once again relative to the observer?

danielatha4 said:
If someone is traveling close to the speed of light, relative to your reference frame, then the time observed on their clocks slows. But what does that mean when it comes to aging? Do their cells that make up their body replicate more slowly?
Sure. Every process in the moving frame slows down according to the observing frame. (Of course, in the moving frame itself everything operates as usual. In fact, they see your clocks and bodily processes running slowly.)
Is there any type of disagreement in the amount of cells replicated in their body between your reference frame and theirs?
Not sure what you mean by "disagreement". Say that the rate of cell reproduction is 5 cells per hour. So, in one of your hours(note), 5 cells replicate on your body and only 3 cells replicate in the moving frame body according to you. Everyone agrees on this.

What's more, the situation is completely symmetric (assuming the moving frame doesn't turn around and come back). The moving frame says the same thing about your cells. How can that be? To understand how they both can say these things requires you to understand not just time dilation, but the relativity of simultaneity. Note that the two events, the start of the first cell replication and the completion of the third in the moving frame, take place at different locations according to you, thus different 'clocks' must be used to record the time that they occur. The moving frame will see your clocks as being out of synch.
danielatha4 said:
Which only allows about 3/5 of the replication of the same type of cell in the reference frame of the observer. Therefore, for every 5 cells replicated on your body, you only observe 3 replicated on the person traveling .8c with respect to you.
Sure. But see my comments above.

(Note: One of your hours as reckoned by you. The moving frame will see the time on your clocks change by a much smaller amount during the time that three cells have replicated. The relativity of simultaneity strikes again.)

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danielatha4 said:
There is less of a difference in time between events one and two for someone traveling an appreciable fraction of the speed of light relative to an inertial frame and IN the inertial reference frame that is observing. Is this not right?
No.This is wrong.

The duration of a second in your frame of reference is one second. The duration of a second in the traveller's frame of reference is one second. Period.

You are mistakenly applying some sort of "universal" time passage to both participants.

Einstein's theory of relativity postulates that his frame of reference is exactly as valid as yours. i.e. you here on planet Earth have no special claim to any universal passage of time. From the frame of reference of the spaceship, it is stationary and you on Earth are moving away at near c.

Apparently some people think that time dilation is a real slowing down, whereas it is really only an effect of observation between two different inertial frames.
In Special Relativity, all inertial frames are equal; none can be considered an absolute reference for any other.
Ron

W.RonG said:
Apparently some people think that time dilation is a real slowing down, whereas it is really only an effect of observation between two different inertial frames.

Including Einstein, the majority of physics graduates, postgrads and PhD's, and the guys who ran this experiment

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W.RonG said:
Apparently some people think that time dilation is a real slowing down, whereas it is really only an effect of observation between two different inertial frames.
In Special Relativity, all inertial frames are equal; none can be considered an absolute reference for any other.
Ron
Ron, you need to stop making false claims about SR. It's OK to be confused and to ask questions about the things you don't understand, but it's not OK to repeat the same mistakes over and over after they've been pointed out to you.

No one is saying that time is slowing down in an absolute sense, or that there's a preferred frame. When A's clock is slow in B's rest frame, B's clock is slow in A's rest frame as well. Both are correct to say that "the other clock is slow". That's not a statement about something absolute. What the statement really means is that the coordinate system that's naturally associated with B's world line is assigning time coordinates to the events where A's clock is present that are higher than the numbers that are displayed by A's clock at those events.

These are not controversial claims. Everyone who understands SR agrees that this is what SR is saying.

W.ron.G said:
Apparently some people think that time dilation is a real slowing down, whereas it is really only an effect of observation between two different inertial frames.
I agree. Time dilation is an observer dependent effect, differential ageing is not.

(Fredrik, did you misread this post, perhaps ? It doesn't seem controversial.)

Fredrik said:
... No one is saying that time is slowing down in an absolute sense, or that there's a preferred frame. ...

actually that is what several posters are claiming.
Ron

No one is saying that time is slowing down in an absolute sense, or that there's a preferred frame. ...
W.ron.G said:
actually that is what several posters are claiming.

Name names. Who is claiming this ?

Mentz114 said:
Name names. Who is claiming this ?

Since you asked, check out 'atyy' and 'sylas' in the thread I linked earlier, and apparently 'TcheQ' above. Not sure where 'stevmg' stands, seems to be leaning to the other side as well.
I think the difference between me and Fredrik is semantic, where I say clock B appears to observer A to be ticking slower, Fredrik says that clock B is ticking more slowly in A's inertial frame. as long as he doesn't believe clock B actually slows down in its own ('B') inertial frame, then we are on the same page. that's how I read his postings.
Ron

another one early on. 'Ich' typed:
"This is not about the aging process, and not abhout different conditions the twins have been living in. For one twin, 10 years passed, for the other 5. With all consequences."
Ron

There is a problem here over the use of language. When people try to answer questions such as "Is time dilation real?" or other variants, different people interpret the words in different ways. There's no unambiguous definition of "real" that everyone agrees with.

If two observers begin together, then separate, then come back together again, then there is no doubt, experimentally, whether the two observers have elapsed the same time or not. You just look at the two clocks , which are both co-located, before and after, and read off the values. In this case we are not making any instantaneous comparison of clock rates, we are comparing the two average clock rates over the whole journey.

On the other hand, if you want to compare two clocks which are separated by a distance, there is no unambiguous way of doing this. To make an instantaneous comparison you need to read both clocks simultaneously, and in relativity different observers disagree over what "simultaneous" means, with no one definition taking priority over any other. Thus whether clock A is instantaneously ticking faster, slower or at the same rate as clock B depends entirely on who is making the comparison. There is no absolute answer to that question.

In the case of the twins' paradox, everyone agrees that the traveling twin (who is not inertial for at least part of the journey) ages less than the stay-at-home inertial twin averaged over the whole journey, but observers disagree over the instantaneous rates at any point during the journey.

DrGreg said:
... In the case of the twins' paradox, everyone agrees that the traveling twin (who is not inertial for at least part of the journey) ages less than the stay-at-home inertial twin averaged over the whole journey ... .

there's another one.
I think y'all need to hash this over and decide which version of Special Relativity you believe in - the one where all inertial frames are equal, or the one where some inertial frames are more equal than others.
Either way it's been an interesting weekend. Toodles.
Ron

W.RonG said:
there's another one.
I think y'all need to hash this over and decide which version of Special Relativity you believe in - the one where all inertial frames are equal, or the one where some inertial frames are more equal than others.
Either way it's been an interesting weekend. Toodles.
Ron
You seemed to have missed the point that one of the twins accelerates and thus does not remain in a single inertial frame. Basic stuff.

W.ron.G,

I think you might be conflating two phenomena

1. Time dilation : where two IRFs see one and others clocks running slower. This depends on the relative speed and seems paradoxical ( but isn't ).

2. Differential ageing : this is not dependent on relative velocity at one instant, but the proper length of the journeys before the clocks are brought together and compared. All IRFs agree on this.

This is what DrGreg and earlier posts are saying.

W.RonG said:
there's another one.
I think y'all need to hash this over and decide which version of Special Relativity you believe in - the one where all inertial frames are equal, or the one where some inertial frames are more equal than others.
Either way it's been an interesting weekend. Toodles.
Ron
Ron, did you look at the numerical example I gave back in post 63 of the other thread? I showed that in an example where one twin (Stella) travels away from another twin (Terence) and then turns around and returns, you can analyze it from the perspective of two different frame, both of which are considered "equal" and which disagree about the rates the two twins were aging during each phase of the trip, yet both frames end up agreeing on the total amount that each twin has aged at the point when they reunite, with the twin who turned around having aged less in total.

As Mentz114 said, you have to differentiate between the rate that each twin is aging (or that their clock is ticking) at a particular moment or during a particular phase of the trip, which different inertial frames can disagree on, and the total time elapsed for each twin during the course of the entire trip from start to finish, which all frames actually agree on despite disagreeing about the rates at different moments. It turns out that in SR all frames always agree in their predictions about local events that happen at a single point in space and time, like two twins meeting and comparing their ages at a single location and a single moment, even though they can disagree about other things like which of two twins is aging faster at a particular moment, or even things like which of two twins that are far apart celebrates their 40th birthday first (this is the relativity of simultaneity, which says that when it comes to events at different locations in space, different frames can sometimes disagree on which happened earlier and which happened later...so different frames can disagree about which twin is older when they're far apart, just not when they actually meet at a single location).

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W.RonG said:
I think y'all need to hash this over and decide which version of Special Relativity you believe in - the one where all inertial frames are equal, or the one where some inertial frames are more equal than others.
All inertial reference frames are equal and they are related to one another via the Lorentz transform. The proper time elapsed by a clock is a Lorentz invariant and all reference frames agree on its value. In particular, all reference frames agree that the non-inertial twin is the one that ages less. I strongly recommend looking into JesseM's example and asking specific questions about any points that you don't understand.

W.RonG said:
DrGreg said:
... In the case of the twins' paradox, everyone agrees that the traveling twin (who is not inertial for at least part of the journey) ages less than the stay-at-home inertial twin averaged over the whole journey...
there's another one.
I think y'all need to hash this over and decide which version of Special Relativity you believe in - the one where all inertial frames are equal, or the one where some inertial frames are more equal than others.
Either way it's been an interesting weekend. Toodles.
Ron
You've just ignored the words highlighted in bold above.

I don't think there's anything for us to "hash over", we all seem to be agreeing with each other, but somehow you're not understanding that. I'm not sure why.

Can anyone get back to my main point?

Did I do my calculations right? and can I clearly assume that for 86400 seconds in my frame, about 53000 seconds has passed in their frame given the initial conditions I stated?

and if so, how would this pertain to aging? particularly if we were to call event 1 the beginning of the replication of a cell and event 2 the ending of the replication.

danielatha4 said:
Can anyone get back to my main point?

Did I do my calculations right? and can I clearly assume that for 86400 seconds in my frame, about 53000 seconds has passed in their frame given the initial conditions I stated?

and if so, how would this pertain to aging? particularly if we were to call event 1 the beginning of the replication of a cell and event 2 the ending of the replication.

I have not checked your calculation but I'm assuming it's correct. I also assume you're comparing clocks that are in the same place. The difference in elapsed time you calculated applies to all processes. Biology is governed by the laws of physics, so ageing, or cell replication or any process biological or other, would agree with the clocks.

danielatha4 said:
Can anyone get back to my main point?

Did I do my calculations right?
If the cell is moving at 0.8c in your frame, and the time between the events on the cell's worldline is 86400 seconds in your frame, then just going by the time dilation equation, the time between these events in the cell's frame would actually be 86400*0.6 = 51840 seconds (the equations in your calculation looked right so it's probably just roundoff error...as a tip, it's easiest to use units where c=1, so if you measure time in seconds, measure distance in light-seconds rather than meters).
danielata4 said:
and can I clearly assume that for 86400 seconds in my frame, about 53000 seconds has passed in their frame given the initial conditions I stated?
The language here is a little ambiguous--when 86400 seconds pass on your clock, it's true that only 51840 seconds pass on their clock (including a biological clock) as seen in your frame. But in their frame, when 51840 seconds pass on their clock only 51840*0.6 = 31104 seconds have passed on your clock. There is no objective sense in which one of your clocks is running slower than the other's.

You can think of this in terms of the relativity of simultaneity, which says that for events which happen at different locations, different frames can disagree about whether they are simultaneous (happen at the same time coordinate) or non-simultaneous (happen at different time coordinates)...in this case, in your frame the event of their clock reading 51840 seconds is simultaneous with the event of your clock reading 86400 seconds, but in their frame the event of their clock reading 51840 seconds is simultaneous with the event of your clock reading 31104 seconds (assuming here that you departed from one another when both your clocks read 0 seconds).
danielata4 said:
and if so, how would this pertain to aging? particularly if we were to call event 1 the beginning of the replication of a cell and event 2 the ending of the replication.
If both of you are moving apart inertially, then each of you will say that the other one is aging slower in your own rest frame. But if one of you stops moving inertially and accelerates to turn around so you can reunite at a single location, then all frames will agree that the one who turned around will have aged less when you reunite.

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danielatha4 said:
Did I do my calculations right? and can I clearly assume that for 86400 seconds in my frame, about 53000 seconds has passed in their frame given the initial conditions I stated?

and if so, how would this pertain to aging? particularly if we were to call event 1 the beginning of the replication of a cell and event 2 the ending of the replication.

Are you aware that time itself is a property of the frame you are in, not some universal property against which all observers are measured? Are you aware that it makes little sense to discuss how long cells take to divide in different frames? If a call takes 3 minutes to divide on Earth then it takes 3 minutes to divide anywhere else in the universe at any speed?

Please - before posting more calculations - acknowledge whether you accept this or whether you reject it.

DaveC426913 said:
If a call takes 3 minutes to divide on Earth then it takes 3 minutes to divide anywhere else in the universe at any speed?
The phrasing here might be confusing...a cell always takes 3 minutes to divide from the perspective of the reference frame where the cell is at rest, not from the perspective of other frames. I suppose you could also say that a cell always takes 3 minutes of proper time to divide, and proper time (the time between two events on an object's worldline as measured by a clock moving along that worldline) is frame-invariant.

JesseM said:
The phrasing here might be confusing...a cell always takes 3 minutes to divide from the perspective of the reference frame where the cell is at rest, not from the perspective of other frames.
Yes. I want the OP to acknowledge this before moving on.

The OP seems to be under the impression that time passes in some absolute fashion such that cell division takes fewer or more seconds depending on how fast you're moving. I wish to disabuse him of this notion.

Mentz114 said:
(Fredrik, did you misread this post, perhaps ? It doesn't seem controversial.)
I took his post to be an extension of what he said in the thread he linked to. In this post, he said that the twins will be the same age when they meet again.

DaveC426913 said:
Yes. I want the OP to acknowledge this before moving on.

The OP seems to be under the impression that time passes in some absolute fashion such that cell division takes fewer or more seconds depending on how fast you're moving. I wish to disabuse him of this notion.

Agreed. Not to mention that as anything within its own inertial frame will have a normal tick rate "to itself at least", the idea of biological effect makes no sense unless you're in MANY different IRFs at the same time (in which case cell division is the least of your worries).

Frame Dragger said:
... the idea of biological effect makes no sense unless you're in MANY different IRFs at the same time (in which case cell division is the least of your worries).

I just noticed this. :rofl: Spot on.. with the bonus of hilarious mental images.

sylas said:
I just noticed this. :rofl: Spot on.. with the bonus of hilarious mental images.

Thank you very much! :) Just remember my name; when the IRFs start-ah-draggin', start runnin'! :tongue:

Frame Dragger said:
the idea of biological effect makes no sense unless you're in MANY different IRFs at the same time (in which case cell division is the least of your worries).
But in fact you are always in ALL possible inertial reference frames and even in ALL possible non-inertial reference frames (with no resulting biological worries) whose coordinate chart includes your worldline.

DaleSpam said:
But in fact you are always in ALL possible inertial reference frames and even in ALL possible non-inertial reference frames (with no resulting biological worries) whose coordinate chart includes your worldline.

Ok, yes... but to be fair that last bit "...whose coordinate chart includes your worldline" is the critical bit in this context. I was of course, thinking of a far more extreme situation, as Sylas realized; say, being in the ergoregion of a Kerr BH. You're right though, and I shouldn't forget the basics.

DaveC426913 said:
Are you aware that time itself is a property of the frame you are in, not some universal property against which all observers are measured?

Yes. In an IRF, a cell that takes, for example, 24 hours to divide (measured by a clock that is at rest to them) will divide in 24 hours in EVERY IRF no matter what. Two people on different sides of the universe will see this cell in their body divide in 24 hours, according to their clock, regardless of their velocity relative to anybody. As long as they have an inertial reference frame. I'm asking the scenario of someone observing someone else's reference frame relatively, in which their clock is no longer local to the cell division taking place.

DaveC426913 said:
Are you aware that it makes little sense to discuss how long cells take to divide in different frames?

Little sense, maybe. Isn't this esentially what the twin paradox comes down to? Everyone interested in physics was probably introduced to the idea of time dilation using the example that someone will age less when moving at significant velocity. I understand that it is a very elementary, and unsophisticated approach, as they don't discuss anything about how the measurements are relative. I'm trying to understand EXACTLY how someone would be younger. I find it logical to believe that for someone to be younger relative to someone then the relativistic observation had to have altered something biologically. At least, relatively, not in anybody's own inertial reference frame.

DaveC426913 said:
If a call takes 3 minutes to divide on Earth then it takes 3 minutes to divide anywhere else in the universe at any speed?

Yes, completely understood. As long as the cell is at rest relative to the observer watching it divide and as long as their reference frame is inertial, it will take 3 minutes. I honestly don't know if I'm COMPLETELY missing something you're trying to tell me.