Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 15/11/2016 11:56:30
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Tuomo Seppala asked the Naked Scientists:
Hello Chris,
I've listened your latest podcast (http://www.thenakedscientists.com/HTML/podcasts/) where you had a question regarding a travel to Jupiter for 50 years and what would be the effect on a human compared to other human beings.
Well that - and many many other theoretical ideas about Einsteins theory of general relativity has been bugging me for quite a while.
In essence the question is; if you travel very fast or close to a massive gravity your time does slow down but does the ageing slow as well? And if yes, how?
Let me rephrase my question;
Say we send a hypothetical Mr. Smith close to a black hole to make a hypothetical podcast from there for one hour. In theory, as far as I've understood, once MR. Smith get's back to his home planet everything around him has aged several years (or something like that) but not MR. Smith. (Let's disregard the travelling time to and from this black hole)
But how is it possible that MR. Smith's body has slowed it's "natural" ageing process while on this trip? Do we have some internal clock in our bodies that slows everything down or does the increased gravity slow the cells and genes down?
Obviously it's just a theoretical funny game or idea so the other question is - is there even point thinking this? Well obviously not, but still it bugs me. Can our bodies ageing process slow down in increased gravity or speed according to Einsteins general relativity?
Just a question for your fantastic show! Hope it get's attention :)
Yours Sincerely
Tuomo Seppala
A dedicated listener and science fan from Helsinki, Finland
What do you think?
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The first thing you have to come to terms with is that the difference in aging is not due to a difference in gravitational strength. It is not because gravity is stronger near a black hole that you will age less than someone back on Earth. It is due to a difference in gravitational potential. The Gravitational potential is related to the amount of work needed to move a mass from one point in the gravitational field to another. To illustrate, you need to imagine that you have a uniform gravitational field (one that does not vary in strength with altitude.) If you have a mass, it would take work to lift it against this field from one height to to a higher one, Thus these two different heights are at different gravitational potentials. If we were to put identical clocks at these two heights, Relativity predicts that they will run at different rates, with the higher clock running faster. This despite the fact that, in this uniformly strong gravity field, both clocks are experiencing exactly the same strength gravitational field. This is because time itself runs at a different rate at these two altitudes.
Your body doesn't have to slow its "natural" aging rate near the black hole, as it is aging at its natural rate. It is time itself that runs at a different rate near the black hole than it does back on Earth.
This is likely the largest hurdle most people face when introduced to Relativity; the fact that time itself does not have an immutable, universal rate.
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No, Mr. Smith didn't age any 'slower' due to his journey, as far as I see, if one except the added wrinkling created by his added 'weight, aka gravity' at that 'black hole', eh, that would then give a illusion of him aging 'faster' btw. Hmm, yeah, better forget the wrinkling for this one.
To him it was the rest of the universe 'running too fast'. And he can prove it to you using his wristwatch.
Time dilation is a comparison. Locally defined your wristwatch, or whatever other time devices you have, tells you your time. You need a 'twin experiment' to prove a time dilation, but even then it's about a comparison between different frames of reference. None of them 'wrong', and locally defined, both agreeing on using the same constants, as when measuring a second, or a meter (or 'c').
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the main problem I think people meet, thinking of this, is that they set the 'universe' as some 'golden standard of time', in this case Earth specifically. But relativity doesn't use any universal golden standards, if we except local definitions that we agree on, as 'constants', and the ability of a wristwatch to measure ones time, dubious that one btw, never had a wristwatch that agreed with my telly. Speeds also give time dilations, not only mass.
To see it better, look up Newtons 'absolute time', versus Relativity's definition of 'local time'. time has to be a local 'constant' in all frames of reference (SR) for us to be able to agree on repeatable experiments. Telling me that it isn't, will invalidate all of them trusting in a clock and meter stick. And by that you invalidate the universe's existence too, unless you believe in magic.
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the difference between Newtons 'absolute time' and the definition I use is in how you define a 'whole universe'. You want to keep the Newtonian concepts, then you're in trouble., because then there are 'slow time' and 'fast time', and different observers will furthermore define different 'time rates' to the same objects, depending on their relative speed and mass.
when it comes to 'time' the only way to agree, that I have found, is the one I present above. The one Einstein used, 'local time'. He found 'time' to be illusive, I don't. I trust in his definition of 'c', clocks and meter sticks. As well as locally defined constants, etc.Thats how the 'whole universe' comes to be, from our local measurements agreeing with each other, no matter your speed or mass, clocks being locally 'equivalent'. That's what creates our constants.
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My own view is that Einstein found time to be a illusion because he wanted 'one measurable universe,' as he looked out on it, not so different from Newtons dream actually. Finding the main thing bothering him in his own theory being the way 'time fluctuated' inside it. He wanted a 'whole reasonable universe'. and I can agree with that vision, but I think Quantum mechanics, 'spooky actions at a distance', string & loop theory, holography etc, etc, offer us new ways of reaching it.. There are more ways than one to skin a cat Horiatus :)
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The body is a bunch of chemical reactions. The simplified question is therefore: will hydrochloric acid react with sodium hydroxide when mixed in a test tube travelling at the speed of light, or will the mixture remain as two different liquids?
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The body is a bunch of chemical reactions. The simplified question is therefore: will hydrochloric acid react with sodium hydroxide when mixed in a test tube travelling at the speed of light, or will the mixture remain as two different liquids?
The test tube cannot travel at the speed of light. At a constant velocity infinitesimally slower than the speed of light the reaction may well take a period of time greater than the lifetime of the universe. This would be indistinguishable from not happening at all.
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Thank you. Is there proof that chemical reactions will slow down at increasing speed of motion? If so, then aging (a bunch of chemical reactions) will slow down.
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Thank you. Is there proof that chemical reactions will slow down at increasing speed of motion? If so, then aging (a bunch of chemical reactions) will slow down.
Physicists now use high speed accelerators to perform reaction at near speed of light where they slow down and it is easier to observe what is happening.
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Got it. Thank you both for your replies. As a biologist, the "rate" usually contains dt in growth and deveopment studies, but aging, or the rate thereof, with or without dt, is much more due to cumulative environmental effects than to dt. You provided insight.
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This is relevant to thing's like the twins paradox. One returns younger than the other, because one has experienced more physical change than the other.
This still leaves me wondering about the extent to which we can argue that time undergoes any chance. Clocks tick more slowly, chemical and atomic reactions slow down, but all this tells us is that physical change is influenced by changes in speed or gravitational potential. Time is what we use to measure those changes, but does time actually undergo any change?
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I will try to explain my "light bulb" moment: Biological growth is sigmoidal when expressed on time (seconds, minutes, days, years, etc.). After the mid inflection point, growth rate declines to a flat line until life ends. Expressing growth on time (as above), is simply a covenient expression: it can be expressed on other independent variables. Then, a body, totally shielded from (negative) environmental effects, will age (deterioate) at a slower rate than its identical counterpart exposed to the environment onslaught. Time, as counted in revolutions around the sun, divided into convenient fractions, can easily change, but age and ageing is dependent to the bombardment of the body by the environment. One can argue that DNA has a half life, largely affected by environmental factors. This is inline with classic genetics,where the degree of heriditabilty (h squared) is defined as sigma g over sigma p, where sigma p equals sigma g plus sigma e. With chemical reactions slowing down, so will equal-environmental aging slow down. Remember: h squared is never 1.
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That seems straightforward (at least the bits i understand do).
Wouldn't that imply that if time dilation caused a body to experience less time, it would be subjected to less deterioration?
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I would say so, given a well isolated "tin can" for the traveller. I am starting to think in terms of a "period", rather than the duration of the period, where duration is simply dependent on the velocity of motion, with velocity expressed as a fraction of the speed of light, not as measured in familiar units such as meters and seconds, which are measurements of the same thing. One can almost think of the speed of light as a current expression, in terms of how long a meter is today and how long a second is today; these units may not be the same tomorrow. They are simply convenient and comprehendible to use as measures in our extremely limited lifespans.
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Obviously, time dilation and length contraction alter the local/relative values of metres and seconds, but are you looking at some sort of global change of values?
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Currently still applying my mind to that, no solutions yet. I will inoculate some young minds with the thought that the "speed of light" is the only constant and listen intently to the outcome. Again, I want to express my appreciation to everyone contemplating this.