Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 16/07/2012 22:30:02
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Alex Williams asked the Naked Scientists:
Dear Chris:
I have read that the greater the gravitational field, the more time slows relative to an outside observer who is at some distance and who is therefore subject to weaker gravity. Is the gravity at the center of the sun or any other star great enough to affect the rate of fuel consumption relative to observers on a planet such as Earth? In other words, if gravity had no effect on time, would a star use up its fuel at a faster rate than is currently observed? And if gravity in a star is great enough to have such an effect on time, how significant is it?
Thank you for considering my question.
Alex Williams
What do you think?
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Again I have to stress is that time dilation of this nature is only a property associated with a remote observer for the centre of the star itself time flows perfectly normally. For the small gravitational fields of stars any time dilation is also negligible and only becomes significant when the gravitational field is very close to being that of a black hole. Also gravitational effects are mostly seen a a red shift in the radiation escaping from the field.
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So true :)
A time dilation is what you measure using your own wristwatch as a definer of 'time'. And we have them on Earth too, gravitationally. But we don't notice them, as finding it troublesome to function due to such.
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Keep in mind that while pressure increases as one moves towards the center of a body, gravity does not.
In the center of a star, pressure would be tremendous. But gravity would be net ZERO.
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Keep in mind that while pressure increases as one moves towards the center of a body, gravity does not.
In the center of a star, pressure would be tremendous. But gravity would be net ZERO.
Also keep in mind that time dilation depends on gravitational potential rather than gravity.
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Yes, time does go more slowly in a strong gravitational field, but the effect only becomes significant in a really intense gravitational field, like near a black hole. So it wouldn't measurably affect the lifetime of the Sun.
For an example closer to home, the GPS navigation satellites have to take this effect into account - since time goes more rapidly when they are at their operational altitude of 20200km/12600 miles: by 45 microseconds per day.
For this and some other relativity effects on GPS, see: http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html