tag:blogger.com,1999:blog-3993498847203183398.post4351833392277017618..comments2024-03-28T09:19:27.451+00:00Comments on RevK<sup>®</sup>'s ramblings: Sci-fi and time dilationRevKhttp://www.blogger.com/profile/12369263214193333422noreply@blogger.comBlogger3125tag:blogger.com,1999:blog-3993498847203183398.post-6651343542696314842023-03-07T17:29:39.115+00:002023-03-07T17:29:39.115+00:00You may enjoy "Mr Tompkins explores the atom&...You may enjoy "Mr Tompkins explores the atom" - a book predicated on the effects of changing various physical constants in Mr Tompkin's world. (See Wikipedia for more info).Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-3993498847203183398.post-28820372529577913822023-03-06T13:52:59.299+00:002023-03-06T13:52:59.299+00:00Oh there's a lot to unpack here. Firstly, ther...Oh there's a lot to unpack here. Firstly, there are *two* sources of time dilation, acceleration and the local gravitational gradient. The second is a property of location, but the first is a property of rate of change of velocity. (They both point in the same direction, because of the principle of equivalence, so they cannot "balance out", they can only make each other stronger).<br /><br />Simply being in a sufficiently dilated environment can eventually kill you from blueshifted light, but it's hard to see how you could get into such an environment without getting into it killing you in the first place: in both cases the harm is likely to come from other sources, like being hit by objects moving at near-lightspeed with respect to you, being irradiated by perfectly ordinary stationary interstellar hydrogen ions, or being torn apart by the nearby black hole or neutron star's tides.<br /><br />But for a real *gradient* you need to be able to *sense* the difference: we're not talking the external world being dilated, we're talking about parts of your own body running at different speeds to other parts. This would obviously be lethal if extreme enough, but it is thankfully also not a problem in practice. Time dilation due to acceleration can obviously not do this unless different parts of you are accelerating at different rates, in which case you have much bigger problems. By the principle of equivalence, the same applies to time dilation due to the local gravitational gradient: if you are in a place where the local gravitational gradient is changing fast enough across your body for this sort of thing to be noticeable, you will be ripped to bits by tides more or less instantly. Even instantly-lethal 50,000G tides across your body -- the sort of thing achievable via acceleration, briefly, by some gun-launched unmanned drones, and otherwise only by loitering close to neutron stars and small black holes -- would cause a time dilation difference of fractions of a second per year. This would not be the thing that killed you :)<br /><br />Its also true that gravitational gradients can be caused by many things: only one of them is the presence of mass. Gravity is produced not directly by mass but by the flow of energy and momentum through spacetime. There are sixteen components in the stress-energy tensor and only one of them is mass... mind you, the others are usually negligible: the contribution of, say, the pressure inside the Earth to its own gravity is very small. (But this does become very significant in large stars and is one of the things that forces large-enough neutron stars to collapse to black holes. Again, if you're in a position to care about this affecting you directly, you have bigger problems.)Nick Alcockhttps://www.blogger.com/profile/06590610308528769844noreply@blogger.comtag:blogger.com,1999:blog-3993498847203183398.post-25520060433718750782023-03-05T17:10:12.296+00:002023-03-05T17:10:12.296+00:00IIRC the flashlight as weapon with time dilation w...IIRC the flashlight as weapon with time dilation was a plot point in one of Niven's Known Space stories. I think it was The Long ARM of Gil Hamilton, but could be wrong.Anonymousnoreply@blogger.com