# B Gravitational Effects on Aging

#### Benfield

Summary
Gravity and ageing
Summary: Gravity and ageing

Hi I am new here, please may I ask,

A celestial object creates gravitational pull, as the universe is expanding and accelerating, the spaces between objects unaffected by gravity, are they subject to ageing. A craft on a course towards an area would occupy those spaces, not near orbits or gravitational pull. The craft itself would not generate gravity, and would be out of orbits. Obviously the occupants would be blasted by radiation but would the occupants age? Thanks for your time.

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#### davenn

Gold Member
Hi and welcome to PF

Summary: Gravity and ageing

The craft itself would not generate gravity,
of course it would, ALL mass generates/has gravity

Summary: Gravity and ageing

Obviously the occupants would be blasted by radiation
What radiation ? where from ?

#### Ibix

the spaces between objects unaffected by gravity,
Gravity has infinite reach, so there isn't any such place, really. Gravity becomes negligible (at least in some senses) but it never vanishes.
are they subject to ageing
Of course. Do you have some reason to think biological processes would stop in the absence of gravity?

#### Benfield

Would you age as fast, sort of slowing as you enter weaker gravitational forces and speeding as you get closer to strong gravitational forces. If you approach a black hole does time not slow? Thanks a lot for your help, I am home schooling my daughter, and appreciate your time.

#### Ibix

Would you age as fast, sort of slowing as you enter weaker gravitational forces and speeding as you get closer to strong gravitational forces.
Not really, although this is a fairly common way of describing things in popsci (even from people who know better). You always age at one second per second, wherever you are. Your own aging and sense of elapsed time is a crude clock, and all clocks tick at one second per second. That's what clocks do.

However, it turns out that if you and I agree a way to start stopwatches at the same time (there's a lot of devil in that detail) and then later we compare our watches we may find that they don't agree about how much time has passed. All other things being equal, the watch lower down in a gravitational field will show less elapsed time, for example.

The important thing to realise is that your own watch will always look normal to you. Time dilation is genuinely something that always happens to other people. So if you look up at me my watch ticks faster, or if you look down at me my watch ticks slow.

The effect is tiny under normal circumstances - back of the envelope if you go into deep space and then we synchronise watches then over two years you will get an extra second. But it is detectable with atomic clocks in the lab.

If you are teaching your daughter, you might want to look for some rather old books by George Gamow about "Mr Tompkins", or a couple of twenty-something year old books by Russel Stannard about "Uncle Albert".

#### MikeeMiracle

The time slowing down is all relative to where you are measuring it from. You would age as fast as you would normally age no matter where you are, it is an external observer that would percieve your time to be slowing down.

Lets give a brief example, lets say there is a black hole by the moon. Your friend goes to the moon for a day trip. According to you 24 hours later you have aged 1 day and your friend is not back, . According to your friend, only a few hours have passed for him and he is still travelling to the moon. It may be several weeks before he returns according to yourself, but when he does get back, he has only been gone 24 hours as far as he is concerned and his body is only 1 day older than when he left. From your perspetive he has been gone weeks and you have aged several weeks while he has aged only a day.

So this is all relative, time has slowed from your perspective. If he was destined is live for exactly 80 years, according to him he will still live exactly 80 years. If he lived near this black hole by the moon, he will still live exactly 80 years. It's just from our perspective looking at him, centuriesd would have passed in our time while only 80 years have passed for him.

Locally, time always runs at the same rate, it's just the perception of someone watdching that changes.

#### MikeeMiracle

Got beaten to the reply.

#### Benfield

Not really, although this is a fairly common way of describing things in popsci (even from people who know better). You always age at one second per second, wherever you are. Your own aging and sense of elapsed time is a crude clock, and all clocks tick at one second per second. That's what clocks do.

However, it turns out that if you and I agree a way to start stopwatches at the same time (there's a lot of devil in that detail) and then later we compare our watches we may find that they don't agree about how much time has passed. All other things being equal, the watch lower down in a gravitational field will show less elapsed time, for example.

The important thing to realise is that your own watch will always look normal to you. Time dilation is genuinely something that always happens to other people. So if you look up at me my watch ticks faster, or if you look down at me my watch ticks slow.

The effect is tiny under normal circumstances - back of the envelope if you go into deep space and then we synchronise watches then over two years you will get an extra second. But it is detectable with atomic clocks in the lab.

If you are teaching your daughter, you might want to look for some rather old books by George Gamow about "Mr Tompkins", or a couple of twenty-something year old books by Russel Stannard about "Uncle Albert".
Thanks to you both MikeeMiracle and Ibix

#### Benfield

Thanks to you both will have a look a those books mentioned, want to give you both thumbs up or likes not sure how it works, thanks again Max

#### Ibix

Lets give a brief example, lets say there is a black hole by the moon.
Just to note that the numbers in this example are wildly unrealistic. You need a supermassive black hole to be able to achieve this kind of time dilation without being killed by tidal forces, and I'm not sure there's an available trajectory that will do exactly what you say, at least not without doing the maths. The principle is broadly correct (the guy who flies by the black hole, and all of his clocks, will record less elapsed time than the stay-at-home) but the details aren't.
time has slowed from your perspective
Part of the problem with popsci descriptions of this kind of scenario is that "time has slowed down" doesn't really have a coherent meaning. What's happened is that one person has used a route through spacetime between meetups that involves less elapsed time for the other. It's actually very closely related to taking two different routes from one city to another. One route might be shorter than the other, but you don't say "distance has decreased for one traveller". You just say he took a shorter route.
it's just the perception of someone watdching that changes.
It isn't a perception really, because that makes it sound like it's all in your head. It's not. What you will see if you watch the other guy's clock is completely predictable and agreed by observers without access to the workings of your mind. You could say it's a matter of perspective how your clock ticks - you will always see it tick normally, but someone else with a different position or velocity will see something else.

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#### MikeeMiracle

@Ibix I know it's wildly unrealistic and would not post that to a proper scientific inquiry, mainly because I do not have all the knowledge to do so. In this context however the poster appears to be looking for a basic level bit of guidance and that is why I gave this over simplified response to help them try and grasp the concept, nothing else.

EDIT: Agree I should not have used the word "perception"

#### Ibix

@Ibix I know it's wildly unrealistic and would not post that to a proper scientific inquiry, mainly because I do not have all the knowledge to do so.
But in that case it's important to say that you made up the numbers. Otherwise people come away with the idea that you've actually calculated some specific scenario.

It's very important to be clear about the limits of your (or our) knowledge when you are aware of them. That way, people learn that they can trust us when we say something, because they know we'll say when we don't know.

#### MikeeMiracle

@bix: Understood & agreed, in future i will do so. I should have stated it's a vast over-simplification purely for the purpose of demonstrating the concept.

#### Dale

Mentor
I am home schooling my daughter
In this case a lot will depend on her background and the educational goals. Specifically, what math and physics has she already studied? I don’t think I would introduce relativity until after some classical physics, and she will need algebra and conic sections at a minimum, with linear algebra, vectors, and calculus strongly recommended.

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