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1 minute to deliver a baby in speed of light ?

  1. Feb 11, 2012 #1
    First please forgive me, if my question is in the wrong board.

    Dear members.

    I'm only Junior High School graduated. So I knew nothing about physics /science/math, etc.

    My friend "teach" me that if a person mr. X move at the speed of light, then time not exist anymore for mr.X or time freeze. So mr.X stay young.

    As I realized he knows that because he read/heard from someone, I feel useless to ask what I'd like to know. So I can't help to become a member here just to ask my question :

    The scientist make an experiment, they have a speed-Of-Light rocket which computerized that regardless time happen during the journey the rocket will always sync the clock with the earthly clock.

    Scientist don;t care what happen to the time duration during the rocket journey also don;t care much how long the distance the rocket feel, what destination the rocket go... they just care that
    the rocket must calculate - by the time it reach 4 earth-years calculation, the rocket-computer "know" that rocket must already landed back on earth.

    The rocket carry a one-hour year old baby and a lady who in 1 minute deliver a baby.

    So the rocket "go somewhere" with the speed of light... and the rocket come back 4 earth-years later to the earth.

    will the baby still a baby ? (1 hour age)
    Will the lady still had her baby inside her womb ?
    (as my friend told me time freeze at speed of light).

    It's really hard for me to think like the question.
    IMHO, people/baby grow and woman deliver a baby is a nature regardless a time/ a speed.

    I'm sorry if it;s a wrong question or ridicolous question and please forgive me my bad english.

    Any kind of respond will be greatly appreciated, and I hope it's not involving physic/math/science - but a light explanation that people like me can understand although a little ... :)

    Thank you in advanced.

  2. jcsd
  3. Feb 11, 2012 #2


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    No. The passage of time is dependent on relative velocity.

    The short answer to your question.

    Your friend has a couple of things wrong. Nothing with mass can ever reach the speed of light, though it can come arbitrarily close. And time will never actually stop in the rocketship.

    However, he is essentially correct. In a spaceship traveling relativistically very close to the speed of light, time aboard the ship from Earth's point of view will tick by very slowly. Indeed, passengers on the rocketship will be younger upon their return than their peers who stayed on Earth.

    If you take this beyond all practical ability, (i.e. you could never accelerate and decelerate fast enough), you could in principle have only a month pass aboard the spaceship while a century passes back on Earth. The passengers aboard the spaceship would come back to find all their friends long since passed away. In fact, if the trip lasted long enough, they could outlive the human race. (And many such stories have been written with that as the plot).

    The problem with your friend's scenario (only a minute passing) is that you cannot in any conceivable way accelerate to .999999999c and decelerate again in less than a minute.
    Last edited: Feb 12, 2012
  4. Feb 12, 2012 #3


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    Since you don't want an answer with math, I won't show you the simple formula to calculate relative aging as a function of speed (as a fraction of the speed of light) but here is a graph that shows the function:


    Here's how it works: you select the speed that the rocket travels at relative to the earth. As Dave pointed out, you can't actually go at a speed of 1 (all the way to the right hand edge of the graph) but you can come as close as you want. However, it's very difficult to tell what the actual numbers are on the graph when you get so close to the right hand edge so let's just say that the rocket is going at 80% of the speed of light. That would be a speed of 0.80. Then you go up to the curve and you see that the age is 0.60. That means that if 4 years passed on the earth, 0.60 times 4 or 2.4 years will pass for the travelers on the rocket. At a speed of 0.90, the age is around 0.44 times 4 or 1.76 years. I think you can see that at a speed of 0.99, the age is around 0.10 or .4 years. At a speed of 0.999, it's going to be very small but it's hard to tell exactly how small.
  5. Feb 12, 2012 #4


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    Boy do I wish graphs like this were on logarithmic scales...
  6. Feb 12, 2012 #5
    Hi Dave and ghwellsjr,

    Thank you very much for your respond and explanation - though I still can not figure out what exactly means :).

    Anyway, in general am I right to say that when someone travel in speed - the speed will influence his/her biological growth ? ---> which is speed "delaying" the biological growth.

    Can I conclude that someone who flies around the world almost everyday, he/she will be younger than the one that never fly ?
    Say... suppose that everybody who never fly will die at 75 yo, but the one who always fly will die at more than 75 yo ?

    I'm sorry.. I change my first question a little bit.
    If the woman before she travel with the rocket is 1 month old pregnant, so she has to spent 8 more months to deliver the baby if she stay on earth.

    The rocket has 2 kind of calendar-clock.
    Clock A - is a regular clock 60 times ticking in 1 minute
    Clock B - is a synchronized clock, which is always sync to the earth clock.

    Am I right to conclude that during the space journey :
    Clock A - the ticking will go slower compare the ticking on earth ? (say, it will ticks 30 times in a minute in average).

    Clock B - since it always sync the clock on earth,
    this clock can show exactly 60 times ticking in a minute where ever the clock is.

    So this woman travel with the rocket on January 1st, and she will see 2 different "time" within this 2 types calendar-clock.

    During the journey, at a "one point" :
    Clock B show September 1st (as exactly as the earth clock which 8 months pass by on the earth), and Clock A show that it is still in May 1st.

    My question is :
    Will the woman deliver the baby at that "one point" naturally ? (regarding the nature growth of the baby inside her womb in fact is ready to be delivered).

    or will she wait until Clock A will show September 1st ?
    If she will wait until Clock A show September 1st :
    - is this because she thinks / her mind tell her it's not 8 months yet ?
    - or is this because the growth of the baby inside her womb delayed ?
    (I mean, if she insist pushing the baby to be delivered at that "one point", she will have a premature baby born).

    another question :
    I just found out that the speed of light is 300K km/sec.
    If say - point A to point B is 2000K km,
    mr.X wristwatch in point A show 1 o'clock (with 1 min = 60 ticking)
    mr.Y wristwatch in point B show 1 o'clock (with 1 min = 30 ticking)

    and the average speed a rocket can reach is 200K/sec.
    Can I conclude that when someone travel with this rocket from point A, he will arrive at point B at 1 o'clock 10 seconds according to mr.X wristwatch in point A ?

    What about mr.Y wristwatch ? is it show the time at 1 o'clock 5 seconds ?
    How does the traveller feel ?
    does he feel 10 seconds pass by ?... or 5 seconds pass by during the journey ?

    I'm very sorry if these kind of questions are weird and can not be proposed as a question.

    btw, dear ghwellsjr - I can;t see the graph picture showed. I don;t know why my page doesn't show your graph picture ...

    Thank you once again for all lovely responder.

    warm regards.
  7. Feb 12, 2012 #6


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    You're thinking about it wrong. Moving at relativistic speeds does not "influence" things. There is no "absolute time" in the universe that Earth's clock is synced to.

    In the rocket, time passes normally. The passengers experience no strange effects. The frame of reference within the rocket is exactly as valid a frame of reference as the one on Earth.

    But if they look out their window, they will see the rest of the universe moving at a different speed from them. And if they fly back to Earth, they will see that Earth's clocks do not agree with theirs.

    Depends on who counts his birthdays. If he counts his birthdays on his own watch, he will die when he is 75. 75 years will have passed for him. But if someone else uses their Earth-based watch, they will count that 80 years has passed between his birth and his death. But if they examine him, they will also note that his corpse is not a day over 75.

    8 months will pass for her aboard ship. When she gets back to Earth, she will discover that the clocks on Earth are fast.

    Note that clock B will have to calculate its time. It will be tied to the propulsion and, as the propulsion changes, the clock will update the speed of its ticking. I point this out so that you get comfortable with the idea that time aboard the ship passes normally, and is a perfectly valid frame of reference.

    No. Clock A will tick normally. However, upon return to Earth, Earth's clocks will be wrong, according to clock A.

    No. Earth does not lay claim to how fast or slow time moves. Clock B will change its rate of passage during the journey.

    Yes, But it is clock A that is correct. Only 5 months has passed aboard the rocket.

    She will experience a normal 9 month pregnancy. Clock A is ticking normally. Clock B, tied to Earth will have changed its rate. If she looks out the window, she will see the Earth's position around the Sun having slowed, such that it is only late spring (i.e. May).

    Neither. Aboard the rocketship, time has passed normally. What happens on Earth does not affect what happens on the rocket.

    The key lesson here is that time is relative to your frame of reference. You always experience time passing at 1 second per second. Changing your velocity with respect to some other frame of reference (such as the Earth) changes the rate of time passage in that FoR as you see it; it does not change the rate of time passage for you.

    Let's deal with this separately.
    Last edited: Feb 12, 2012
  8. Feb 12, 2012 #7

    OH my gosh.... I was wrong all the time.
    This is embarassing as how stupid am I....:)

    I based my conclusion from the article I read somewhere on the net :
    Identical clocks have been used to compare time in motion versus rest.
    The moving clocks run slower than the stationary clocks.
    Physical processes are affected by the passing of time such as chemical and biological processes

    I was focusing at the senctence "The moving clocks run slower than the stationary clocks".
    So I thought the Clock A runs slower (fewer ticks) which is in 1 minute 30 ticks during the journey.
    Then I thought as the woman see and compare the Clock A and clock B during the journey,
    she'll notice/feel that Clock A is always "run late/slower" than Clock B.

    In fact, Clock A runs properly and she'll notice/feel that Clock B is the one which run faster.
    I'm really sorry for my misinterpreation, Dave.

    I wonder :
    suppose by the time Clock A show March 1st and the rocket come back to earth
    So when the rocket landed on earth :
    Clock A show the calendar on May 1st, Clock B show September 1st

    am I right to conclude,
    that the lady still have to wait to deliver her baby for another 4 months ?

    I'm very sorry to trouble you with this stupid question.
    (it needs a superlady-kind to experience this sort of journey... :)).

    Thank you once again, and I really appreciate your time and explanation to me.

  9. Feb 12, 2012 #8


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    No. This is an extremely difficult concept to grasp. Do not punish yourself. You are catching on very quickly.

    It actually is more complicated than this. Sometimes the clock runs slower, sometimes it runs faster, depending on the rocket's path. But it will take a while to tease out the various facets of it. Be prepared for a journey of understanding, of which this thread is but one leg.

    Yes. Which is exactly what she is expecting - a 9 month pregnancy.

    First, let's be accurate about dates.
    Jan 1 to May 1 is 4 months.
    Jan 1 to Oct 1 is 9 months.

    The baby was conceived on Jan 1st. Expected date of delivery would be Oct 1st. On Jan 2, mom gets in a spaceship and flies around at .9c. By her watch, she comes home on May 1. But when she checks Earth's calendars they say the date is Oct 1.

    For mom, only 4 months has passed. Her watch-calendar says it is May 1st. Her baby is only 4 months developed. She has 5 more months of pregnancy. If she chose to keep her watch on ship time, for the rest of her pregnancy, it would tell her that, 5 months later, she will give birth on Oct 1 (her time), just like she's supposed to. She and her unborn baby will have aged 9 months from conception to birth, exactly as she expects.

    But if you ask the people in Earth how much time passed between conception and birth, they will say 14 months. She conceived on Jan1, then disappeared for 9 months. But when she came back home (on Oct 1) she was only 4 months pregnant (not 9 like they expected). 5 months later, on Mar 1, she gave birth.

    During her journey, she aged 4 months, while Earth aged 9 months.
    Last edited: Feb 12, 2012
  10. Feb 12, 2012 #9
    Hi Dave,
    Thank you for your patience.

    In general, I get the point from our previous discussion.

    But I still can't help but thinking about the aging.
    As you said :
    So I conclude that the biological-clock of this lady is not influenced by anything at all. For example, her approx heart beats rate will tick as normal as she is on earth.

    I feel there's something wrong with the concept about the earth show Sept 1st (Clock B) and Clock A show still in May 1st by the time she landed back on earth.

    I don;t know... although I can not describe it in formula as in science, but IMHO - I feel the calculation on the Clock A can not be like that.

    I mean when we on earth say 1 minute consist 60 ticks of sec, I feel that we can not apply the word "minute" as soon as we are out of earth frame.

    The proper calculation for the minute ... (well it's just in my own imagination), I think is better based on the count of how many heart beats of the lady.

    I just google, that the healthy normal people heart beats rate is 70-90 / minute, and suppose the lady biological-clock is like that normal people.
    Am I OK to say that the "better" proper calculation have to be based on the total count of heart-beats of this lady during the journey ?

    In my imagination, if there is another clock which is the lady's heartbeat clock - so by the time the lady calculate her "own calendar" is somewhere 4200 beats, then it seems possible that the Clock B show that approx 1 hour already passed.

    And it goes on....
    by the time her hearbeats count somewhere around 24x4200 beats - then the Clock B show that approx 24 hour / 1 day have passed.

    IMHO, with this heartbeat clock - then it can be the literally (actual) means of what the lady experience during the journey is the same as what human experience on earth.

    So when she landed - her hearbeats count approx 8x30x24x4200 beats = the Clock B shows approx Sept 1st, and what the Clock A shows (May 1st) is only imagination by the calculation according to earth frame.
    The lady is ready to deliver her baby by the time she landed on earth...:)

    Please correct me if I;m wrong Dave.

    Thank you and regards.
  11. Feb 13, 2012 #10


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    No. Earth's clock has no effect on her. The clock on the spaceship is always accurate for her. Earth's clock will get increasingly out of sync with the passage of time on the spaceship.

    You're failing to grasp that the time on Earth applies only to Earth; it does not apply anywhere else, except other places that are stationary with respect to Earth.

    As far as mom is concerned, she is in a stationary spaceship, experiencing no relativistic effects at all, while Earth is moving away from her at nearly the speed of light, and all its clocks are getting out of sync. This is a perfectly valid representation. The clocks on Earth track time that is no more real than the clocks on the rocket.

    Clock A (on the spaceship) does not calculate time. It is a normal clock, counting normal time, at 1 second per second because that's what clocks do.

    It is clock B - the one that trying to keep track of what time it's supposed to be on Earth - that falls increasingly out of sync. It is not actually a clock; it is a computer program that must calculate what Earth time is supposed to be, because it has no way of knowing directly. Earth's time changes, depending on what the ship is doing, and the clock/program must figure this out and display what the time should be on Earth. It does this by getting its position and velocity and acceleration relative to Earth and then performing a transform. But the number it displays is of no more than passing interest aboard the spaceship. It says what time it's supposed to be far away.

    (I can use a program to calculate what the time is supposed to be in Sydney Australia right now. But that number will have nothing to do with what time it is here. And my clock is right for me. Sydney's clock is of little use to me; it only tells me what time it is in Sydney.)

    You must grasp this concept: time on the ship behaves completely normally. A minute is a minute, a heartbeat is a heartbeat. It is Earth that is falling out of sync because the Earth is moving with respect to the spaceship (which is stationary).

    This is what relativity means. It means that there is no such thing as universal time. What is happening on Earth is utterly irrelevant to the occupants of the spaceship. The occupants of the spaceship go about their lives completely normally, as if they are flaoting stationary in space, unaware that anything strange is happening on some far away planet that is moving at a relativistic velocity.

    This is wrong. The Earth clock does not tell her how fast time is ticking by. Earth clock is telling her what's happening on some distant planet far away. That planet is moving relative to her, therefore its time is dilated. The clock on the spaceship counts real time, and her heartbeats and pregnancy match this time.

    Each person - whether on Earth, on a fast comet, a passing rogue planet, or on a spaceship - sees their own time ticking by normally, while everyone else's time is falling increasingly out of sync. And each of them is correct. There is no universal time.
    Last edited: Feb 13, 2012
  12. Feb 13, 2012 #11


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    It might make more sense to think of the rocket as not moving and it is Earth that is flying away from the rocket at .9c.

    In this scenario, whose clocks are ticking by at 1 second per second?
  13. Feb 13, 2012 #12
    I'm sorry, I;m confused to get the meaning of those sentences.
    How will the lady knows that Clock A behaves normally, while it runs sometimes slower sometimes faster ?

    That's why I thought that the Clock A can not be as a reference clock in the rocket ... :).

    Because clock A was made on earth - with all the calculating hours and minutes based on 60 sec.

    But how about once this Clock A is out of earth frame ? Wouldn't the term that we say "normal time" regarding as long as the clock on earth - can not be applied anymore ?

    I'm sorry, I still don't understand.

    So what really happening is actually she literally is the one in stationary, the earth is the one moving away from her and earth clocks are getting out of sync ?


    she thinks she is in stationary and she thinks/feel/see that the earth is the one moving away ? which made the result - she also thinks that all earth clocks are getting out of sync ?

    This is very new for me. I thought, it is the lady who thinks that the earth is moving away from her which cause she also thinks the earth is falling out of sync.

    Please forgive me... I never thought it actually like this.

    I thought as if just like when we are on the train. We see trees, vehicles, etc are passing us - so we think that we are in stationary and those are moving away.

    I'm very sorry... this is really difficult for me to grasp.
    I wonder : how come the people's heart on earth beats more while the lady on her journey ?

    As when the rocket landed - Clock A shows May 1st which means the total heartbeats of the lady is approx 4x30x24x4200 during her journey, but how come the people on earth welcoming her arrival already have their total heartbeats approx 8x30x24x4200 ?

    Do you mean because :
    - so the people heartbeats on earth ticking faster also ?

    I honestly don't know, what does it mean "universal time" ? (don't worry - I will google it now ...:)).

    Please be patience with me Dave.
    Thank you and regards.
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