Years in Space

Factual Questions
1

OK so me and my friend Paul were driving out to Chicago from New York, and we got into this discussion about space travel… and basically the way I learned it was that if you did super long distance space travel you would have to be traveling in a spaceship that goes at near the speed of light…he and I agreed up to that point. Now as I learned it in my astronomy class circa sophomore year, if you travel at near the speed of light, time itself passes for YOU at a slower rate than it does for people back on earth. So the upshot (and this is where me and Paul disagreed) was that a space traveler gone for what to him seemed like 5 years would come back to earth and find that everybody is 40 years older now. (those aren’t actual numbers but its along those lines basically). Paul (a way better read guy than me) says no, no way. My understanding is that time is also part of relativity, not just space & matter, and that we age within time (and gravity).

So later my friend Matt said: “You were correct. That’s all the theory of relativity is: time moves slower relative to another object. The proof of this was in the 50s or 60s when an atomic clock was put aboard an aeroplane. When the plane landed, sure as shit on a farm, the clock was a couple milliseconds (probably even smaller increments but who’s counting?) slower than earth time. (see: http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/airtim.html )”

But then Paul said: " I still don’t see where the aging process has been addressed…The space ship you are travelling in may be traveling at light speed, but the relative difference between the molecules of your body due to aging would be the same as on Earth. Which is why you even age at all (5 years in your example). I understand an atomic clock is based on the rate of decay of an inorganic element. But what about organic matter that is subject to environmental factors? The crux of my argumenent is that there is a difference between the passage of time, and aging. Aging we conveniently measure in terms of time, but we also measure mass in term of weight, also because it’s convenient, even though they aren’t the same thing when gravity, a relative factor, is changed. "

SO… is the process of aging governed by time? Are all our super-astronauts gonna return in 50 years having aged only 6?

2

Organic matter will feel time exactly the same as the inorganic atomic clock. Therefore the astronaut will age less than everyone else back on earth. However much time is measured by a clock the human will have lived for and experienced so therefore aged. Time governs aging and it doesn’t matter about anything else being different.

3

There are a lot of possible answers to I’ll see what sticks. If the process of aging is not goverened by time what else would it possibly be governed by?

In the end you’ll gain a better understanding by learning more about the nature of time and space dilation under relativity. The plane and clock experiment, which was done in a 747 BTW so it was done more recently, is one experimental validation of time dilation. Understanding more about the underlying theory will make it less abstract.

4

Yes, the organic aging process is goverened by time. The point is that we determine what someone’s age precisely by the amount of time they have been alive. It doesn’t matter what their weight, height, eye-color, or number of wrinkles in their forehead is. It is an objective measure.

If Paul meant to point out that the astronauts might not age well… Well, that’s up for debate. Indeed you do have different environments, but now you’re getting into the whole bit about the evidence for people’s age. This doesn’t change one bit the fact that measured objectively, time have passed “more slowly” for the person we send on a voyage close to the speed of light.

To put it another way, if someone on earth and someone in rapid rocketship had exactly the same pulserate, the rocketeer would experience fewer heartbeats than the earth-bound cousin over the period of the trip. Even so, the person in the rocketship might keel over dead (thus aging poorly) before the end of the mission while the person left on earth might be a healthy senior citizen (thus aging well).

5

Isn’t the man whos been in space the longest 1/50 of a second younger than he should be? I heard this on the Space Channel so I can’t really authenticate it.

6

OK so Paul wrote me back about this, but he’s very shy and won’t post here himself for some strange reason. Anyway he said:

“Still no one yet has responded to my point. I think everyone is still focused on the relative angle of time without dealing with the biology, which is all that matters, right? I mean, that’s the assumption underlying the question of doing the space travel, making the big money, and coming back still physically young to a much older earth.
But JS is the first to at least touch on what I’m actually talking about- the actual changes the body undergoes. He calls this “aging well”, I would simply call it aging. A simple way to describe my point is, the organic change the body undergoes during interstellar travel is not going to be that different from that here on Earth. When he says we determine age by the amount of time they’ve been alive, I agree, never disagreed, in fact. But when you say someone has only aged 5 yrs during space travel when 40 years have elapsed on Earth, what you really mean is that the astronaut has undergone the same amount of biological change as they would have during 5 years on Earth. When JS says, “now you are getting into the whole bit about the evidence for people’s age,” I say, YES! That’s what this debate is all about.
So, all I’ve seen so far is several people make an assumption (“aging is governed by time”), then prove their point by re-stating that the assumption has to be true (“what else would it be governed by?”). What is the proof that aging is governed by time? Is it because we believe the universe only exists in terms of time, mass, energy? Therefore every aspect of existence must adhere to our current level of understanding? What about the things that we can’t explain (and I’m not just being metaphysical here)? It seems like my point addresses something that we can’t explain (aging), but the responses mostly try to use a tool (Relativity) that is meant for another job.”

7

If this is a science question then the human body aging is an organic clock. It has lots of processes and cycles that change over time. Just because the astronaut is organic doesn’t mean hes not governed by the normal chemical reactions etc that inorganic matter is. These reactions and processes take set amounts of time. Aging MEANS how the human body changes with time. We have no reason to introduce something we can’t explain cos we can explain aging quite well.

8

We don’t allow posting through proxies here. If Paul wants to make his point, whatever it is, he can register here and do so.

9

Human aging is biology, yes. But biology is based on chemistry which is in turn based on physics.

“Is it because we believe the universe only exists in terms of time, mass, energy? Therefore every aspect of existence must adhere to our current level of understanding?”

If you want to talk about science, we need to limit ourselves to what science knows. If you want to introduce an element of mysticism or supernatural in the equation, science will not be able to answer your question. OTOH, mysticism do not understand SR.

10

When you ask someone what their age is, the reason they respond to you with a measurement of time is because that is how such a thing is measured. I will leave it to the reader to look in a dictionary as to what “age” means, but I will say that aging as a process is manifestly NOT subjective. It is exactly what happens when time passes. It doesn’t matter whether the thing is living, dead, or in-between, aging happens as time passes. Just because a 90-year-old thinks and feels like a 60-year-old does not mean the 90-year-old is actually 60 years old. The 90-year-old is 90 years old. End of story. Saying aging isn’t about measuring time is redefining what aging is. If that’s the case, it is up to the person who makes the argument that it is different to provide their alternative explanation.

To drive my point home:

If I ask you what the age of the earth is; I’m asking for a measurement of time.

If I ask you what the age of a building is; I’m asking for a measurement of time.

If I ask you what the age of an astronaut is; I’m asking for a measurement of time.

If you want to measure something else (health, wealth, viability, agility, reflexes, skin elasticity, physical well-being, etc.) then you measure those. “Aging” is defined strictly only through the amount of time one has been in existence. Indeed, the point of intiation of existence is semantic, but we generally agree on a common definition of that point (i.e. birthday) to give us a context. This is why the paradox is sometimes called the “Twins’ Paradox”, as naming it such sets a common initiation of existence.

Other than time, there is only correlation of phenomena with aging. For example, white hair is often indicative of old age, but it is not an objective measurement of aging. The only objective measurement available PERIOD is time.

So, if I ask “Which person has experienced less time?” it is EXACTLY THE SAME as asking which person has aged less, the answer is the person in the rocketship.

11

Wearia, indeed the Space Channel in this particular instance is telling you the truth.

12

There is no universal time: the measurement of time is entirely a relative thing. How one ages

I agree with Padeye, what’s needed here to answer Paul’s question is a better understanding of relativity and how that affects time dilation. That’s hard to do on a bulletin board which sadly limits the use of visual representation.

However this lil’ cheeky monkey does just fine without aid of pictures and graphs. http://www.muppetlabs.com/~breadbox/txt/al.html

13

Apologies for my transgression. I didn’t realize. Sorry.

OK now hang on here, Paulie. He said it’s open to debate, not “we don’t know.” To me “it’s open to debate” means it’s open to debate.

Shall we?

So to start, what then is our working definition of “aging” here?

If it’s how many years elapse while you are alive, then this is open and shut. If the clock on the rocket ship wall says 5 years, then it’s five years.

But let’s face it, that’s not actually what we really care about. What we want to know about is becoming biologically aged–coming home in forty years still looking like a stud. Cuz if you go up in space and come back in 40 years looking 40 years older, then that’s not too damn impressive, even if you do point at your clock and say “Hey! See that!?”

So let’s just agree that what we’re talking about going away 40 years and coming back still being able to get laid.

Now about this biological aging and its supposed relation to time. JS gave the example of a pulse. If time passes inside this rocket at its own 5-yr pace, then the heart beats at its normal rate for this amount of time. Are we agreeing on this at least? Otherwise the dude’s heart is racing at eight times normal speed trying to squeeze in all those heartbeats in just five yrs. And the rest of his body would need to do the same in order to “age” 40 years in that time. His hair would need to grow at 8 times normal speed. His cells would need to multiply and die and mutate at 8 times normal speed. All relative to that clock on the ship. And if you haven’t accepted that the clock is an indicator of the true passage of time on the ship, then you haven’t really accepted the idea that time is a dimension affected by relativity. And that, to me, would sound like a personal problem.

Now if this aging was going to be taking place on the ship at this supposed 40 year clip, then would our rocket man (let’s call him “Sir Elton”) be checking out this clock the whole time and wondering why the second hand is barely moving? Because you realize you have two earthly machines (clock, Elton) chugging along within two completely different temporal realities then, while they’re both sitting there in the same room. (yes Elton’s ship has rooms). Why would the clock not also age 40 years? Organic and inorganic materials still obey the same laws of physics, right? If there is something encoded in the makeup of Elton’s cells that would adhere to an earthly timeclock as opposed to the one that he is currently existing in, then why would there not be any such encoding in the clock, which is also made up of earthly elements? You (Paul) talk about the difference in molecules being the same as on earth…but whoa, let’s talk about that. OK we all would agree that in order for Elton to age, his cells must change. That means cells made up of molecules made up of atoms which make up Elton. In order for Elton to age (get white hair, long toenails, look droopy) his cells must change, following the same set of steps they would on earth that would take 40 years to play out there…which means his molecules must change by that much, which means those atoms must move that much. What you’re suggesting is that the molecules inside Elton John are going to accelerate to 8 times the speed of what those inside his bedside clock are moving at. Same atoms under the same environmental conditions. The second hand’s atoms’ electrons moving at one speed, Elton’s love handles’ atoms’ electrons at another. Are you sure you’re not religious? Cuz that to me sounds like a miracle.

Now here’s the tricky part: what if Elton has a pacemaker? On second thought, let’s not go there.

OK another: what if Elton impregnated a woman (hey, it can happen) on the ship while it was traveling at near the speed of light? When that kid moves off the ship to live on earth, is it going to age only 5 years in every 40 after that? or even while still on the ship, traveling at near light speed, will the kid and Elton then age at different speeds? And I’m not even gonna get into the cross-breeding with the race that has only ever lived at near-light-speed.

So what I’m saying is, Elton will come back looking like in his Benny and the Jets days, maybe even with the giant shoes he wore in Tommy… and those 40 earth years will have seemed like only five to him. Yeah we will have missed out on “I’m Still Standing” and all those other later hits, but, I think that might just be yet another great benefit to mankind coming out of this.

14

I think the fact that this time dilation is taking place on a space ship is confusing you. Think of there just being a room on earth where time goes slower. 5 years in this room is actually 40 years on the outside. If you go in there and sit for 5 years when you get out everyone else will have aged 40 years. So if you went in as a healthy 21 year old you would come out at as a healthy 26 year old (unless you get disease or dont eat or something stupid). Where as your 21 year old friend will be 61. There is nothing different about this aging at all. Biological aging is aging full stop. A clock inside the room would measure 5 years and a clock outside measure 40 years. A child born inside or outside the room would always age at the same rate that a clock next to them measures change in time. Also to the guy in the room all the processes outside back on earth are going 8 times as fast. Outside of the room the process inside the room seem to be going 8 times slower.

15

It’s no crime not understanding relativistic time dilation, because it’s been confusing people for a century.

It’s a problem when you don’t listen, however.

Inside of a frame of reference that is moving at a significant percentage of the speed of light, time slows at an equivalent pace for everything that is being affected. That means you, your clock, your spaceship, your food supply.

Say that five years pass on the spaceship as opposed to 40 on earth:

Over that five year period:

your clock would register five years;
you would grow five years older;
a five-year-old child would grow to be a ten-year-old child;
a battery with a five year lifetime would go empty;
a radioactive substance with a half-life of five years would lose half of that element;
you would use up five years worth of food, fuel, water, and reading material.

There is absolutely nothing that would seem out of the ordinary to you about the rate at which time is passing. Everything down to the subatomic level would feel the passage of time in exactly the same way. This would be true even while you are accelerating, decelerating or remaining at a constant velocity. The only way to tell that anything is different is to compare your situation to one that has not been traveling at a significant fraction of the speed of light.

Time is time. It works on everything in the same way.

When we have been saying that you would only age five years, we mean exactly that. No ifs, ands or buts. No exceptions. No philosophical arguments. Time slows. You can’t feel it. But when you returned everybody and everything would be 35 years older than you.

16

Is it possible that the human metabolism would speed up to such an extent as to compensate for the different rate of time passing?

Or stated another way, is it possible that there is a genetic trigger in response to traveling at light speed?

It seems like we know more or less the basic parameters for aging here on earth. But time isn’t a variable factor on Earth. Can we say for certain that the 5 year old child will still be a child, and not a 10 year-old geezer?

17

Yes.

18

Okay, author Robert Heinlein addressed this nearly fifty years ago in one of his juvenile novels, “Time for the Stars.” It’s a quick story about telepathic twins, one of whom ends up on a near-lightspeed spaceship. A fun read, and accurate on all points of the physics.

It’s sad that folks asking about such things never got the basics in school…

19

unequivocally no… not as a compensation.

Absolutely not.

Neither is it in any frame of reference you care to name; spaceship or swamp hole, time marches on at one second per second.

The last question you asked, oooops, was already exquisitely answered by Exapno Mapcase.

20

If accurate on all points, I’m assuming then that said story does not involve instantaneous trasmission of information via this telepathic connection. In other words, the twin’s communications over the period of the trip had to have been time dilated. How strange to get a message in your brain streettcchheeddd oooouuuuttttttt…