# Using black holes to travel into the future, how would this work **URL:** \ **Category:** Factual Questions\ **Created:** [April 7, 2015, 9:27pm UTC](https://boards.straightdope.com/t/using-black-holes-to-travel-into-the-future-how-would-this-work/717072 "2015-04-07T21:27:59Z")\ **Posts on this page:** 8\ **Page:** 3
**Author:** ![gnoitall](https://avatars.discourse-cdn.com/v4/letter/g/bb73d2/32.png) [@gnoitall](https://boards.straightdope.com/u/gnoitall)\ **Post date:** [April 9, 2015, 2:29pm UTC](https://boards.straightdope.com/t/using-black-holes-to-travel-into-the-future-how-would-this-work/717072/41 "2015-04-09T14:29:58Z")
> [@Martian Bigfoot](#): > > Good grief, that must have been interesting. “Hey, thanks for spending a week doing heavy duty black hole physics to get the details of time dilation working realistically. Mind if we shoot every principle of physics that we know about out the window with some FTL travel?” > > Sort of doing a movie about the Civil War and getting every detail of the period uniforms right, only to have the Battle of Gettysburg fought by troops riding T-Rexes with lasers. Well, Picketts’ Charge would have been more interesting (and probably more successful) if it had been a saurian cavalry charge with energy weapons. ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [April 9, 2015, 3:22pm UTC](https://boards.straightdope.com/t/using-black-holes-to-travel-into-the-future-how-would-this-work/717072/42 "2015-04-09T15:22:18Z")
> [@Great\_Antibob](#): > > Haven’t read the book, so I was curious if he dealt with some of the other sticky issues, like the abundance of visible light but not enough other forms of EM radiation to kill the crew (especially if the planet is tidally locked) or how they could land on the planet if it’s orbital period implied a significant fraction of c or, for that matter, why they used a conventional rocket on earth if their shuttle vehicles could hit low orbit so easily? Or was it a matter of getting the time dilation right and fudging some more on some of the other practicalities. The EM radiation question is a good one, and it wasn’t ignored. They assumed that Gargantua had a very “anemic” accretion disk, one that was cool enough to emit lots of light but not a high level of X-rays and gamma rays. Disks like this may exist around black holes that haven’t eaten a star in a long time, and would be thin and mostly confined to the equatorial plane, as indeed Gargantua’s disk was represented in the movie, which was premised on a thin disk but one that was distorted by massive gravitational lensing according to careful simulations that the special effects folks ran. Thorne endorses the idea but credits it to Christopher Nolan and Paul Franklin, the special effects supervisor. The only factual liberty the movie takes here is that Miller’s planet should be within the accretion disk, but they don’t show it that way because it’s a rather spectacular visual effect that they save until closer to the end of the movie – I hesitate to reveal too many spoilers here for those who still haven’t seen it. (Though nothing beats seeing it in the glory of 70mm film IMAX – as opposed to digital IMAX, which is great but not the same. Sadly probably neither is possible any more anywhere). Catching up with Miller’s planet despite its immense orbital speed is not explicitly addressed within the movie but Thorne presumes the _Ranger_ uses a gravitational slingshot from smaller black holes or neutron stars that might typically be in orbit around a supermassive one like Gargantua to deflect its orbit toward Miller’s planet at high speed. The movie does address, however, the subsequent deceleration necessary due to _Ranger_ having fallen into the lower orbit of Miller’s planet, involving a counter-orbiting neutron star: “I can swing around that neutron star to decelerate,” Cooper says at one point. ---
**Author:** ![Great\_Antibob](https://avatars.discourse-cdn.com/v4/letter/g/e47c2d/32.png) [@Great\_Antibob](https://boards.straightdope.com/u/Great_Antibob)\ **Post date:** [April 9, 2015, 3:46pm UTC](https://boards.straightdope.com/t/using-black-holes-to-travel-into-the-future-how-would-this-work/717072/43 "2015-04-09T15:46:50Z")
> [@wolfpup](#): > > The EM radiation question is a good one, and it wasn’t ignored. They assumed that Gargantua had a very “anemic” accretion disk, one that was cool enough to emit lots of light but not a high level of X-rays and gamma rays. Thanks. I hoped there would be some mostly reasonable explanation. > [@wolfpup](#): > > but Thorne presumes the _Ranger_ uses a gravitational slingshot from smaller black holes or neutron stars that might typically be in orbit around a supermassive one like Gargantua to deflect its orbit toward Miller’s planet at high speed. That’s fine, but I meant using the shuttle from the surface of two different worlds (Miller’s and Mann’s) to dock with the _Endurance_ in orbit. Seems like that would have worked just fine from earth, too, obviating the need for their original flashy NASA launch. ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [April 9, 2015, 4:59pm UTC](https://boards.straightdope.com/t/using-black-holes-to-travel-into-the-future-how-would-this-work/717072/44 "2015-04-09T16:59:28Z")
> [@Great\_Antibob](#): > > That’s fine, but I meant using the shuttle from the surface of two different worlds (Miller’s and Mann’s) to dock with the _Endurance_ in orbit. Seems like that would have worked just fine from earth, too, obviating the need for their original flashy NASA launch. You also asked about catching up with a planet whose orbital velocity was a significant fraction of _c_, which Thorne does address, as well as the important high-energy radiation question. I haven’t seen a rationale anywhere for the traditional-looking NASA launch but I wouldn’t consider it a point of science that’s either right or wrong, that’s just how they chose to show it, probably because that’s how most of us visualize a space launch. If you want a physics rationale for it, maybe very large conventional rocket(s) was the most efficient way of getting all the interstellar hardware (including the components of the _Endurance_ itself) with all its fuel initially into earth orbit. I don’t remember if there was anything explicit about how _Endurance_ itself got into orbit. ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [April 9, 2015, 5:17pm UTC](https://boards.straightdope.com/t/using-black-holes-to-travel-into-the-future-how-would-this-work/717072/45 "2015-04-09T17:17:31Z")
> [@wolfpup](#): > > He claims not. I found this in the “Technical Notes” section at the end, although I’m at a loss as to where his relativistic approximation for α comes from, as it’s not explained further than “I have deduced a formula …”. All I can tell you is that the calculation does yield his claimed result: He means that it is just below the extremal limit of 1, but this is still well above the “Thorne limit” of 0.998 for an accreting black hole. Or in other words the black hole has a spin that is far too high to be realistic, but at the same time is not unphysical. ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [April 9, 2015, 6:40pm UTC](https://boards.straightdope.com/t/using-black-holes-to-travel-into-the-future-how-would-this-work/717072/46 "2015-04-09T18:40:30Z")
> [@Asympotically\_fat](#): > > He means that it is just below the extremal limit of 1, but this is still well above the “Thorne limit” of 0.998 for an accreting black hole. Or in other words the black hole has a spin that is far too high to be realistic, but at the same time is not unphysical. OK, I see what you’re saying. With my limited knowledge I can’t infer that for sure from his mystery equation but that’s probably what he meant when he said it was “very unlikely” a black hole could have such a spin, but physically possible. In [this paper](http://iopscience.iop.org/0264-9381/32/6/065001/article), he talks about using a spin parameter of 0.999 for most of the simulations they did, which they slowed down to 0.6 to get more interesting visuals for the accretion disk. The movie takes scientific liberties here and there, and occasionally soars to heights of pure speculation, but to my mind is impressive with how well overall they combined plausible science with the story line. Basically Thorne’s job was to be the guy who, if the scientific basis was challenged, to be accountable for explaining why it’s possible. _Star Trek_ it ain’t – no Klingons, no warp drives, and lots of real science. 🙂 ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [April 9, 2015, 8:06pm UTC](https://boards.straightdope.com/t/using-black-holes-to-travel-into-the-future-how-would-this-work/717072/47 "2015-04-09T20:06:22Z")
> [@Asympotically\_fat](#): > > He means that it is just below the extremal limit of 1, but this is still well above the “Thorne limit” of 0.998 for an accreting black hole. Or in other words the black hole has a spin that is far too high to be realistic, but at the same time is not unphysical. Just looking at the equation in #37 again, clearly you’re right. I withdraw my second sentence above stating that it’s not obvious! I was focused on not knowing how he derived that equation, but it doesn’t matter. You can plug in any desired amount of time dilation. As you approach the limit of S=0, you approach α=0 and the spin parameter approaches 1. So yes, the one part in 100 trillion is relative to the theoretical max spin, not the Thorne limit. :smack: ---
**Author:** ![Asympotically\_fat](https://avatars.discourse-cdn.com/v4/letter/a/e47c2d/32.png) [@Asympotically\_fat](https://boards.straightdope.com/u/Asympotically_fat)\ **Post date:** [April 10, 2015, 10:38pm UTC](https://boards.straightdope.com/t/using-black-holes-to-travel-into-the-future-how-would-this-work/717072/48 "2015-04-10T22:38:31Z")
> [@Asympotically\_fat](#): > > I’d have to look this up, but I’m not sure that this could be the case and Hawking radiation would carry away more angular momentum than mass from the black hole, The reason I believe this is because the Hawking process is the quantum limit of the classical Penrose process which carries away both mass and angular momentum from a Kerr black hole with the overall effect of reducing the spin parameter. Just to confirm this point, I have looked it up and the effect of Hawking radiation is to “de-spin” black holes for the reason I stated. [Previous page](https://boards.straightdope.com/t/using-black-holes-to-travel-into-the-future-how-would-this-work/717072.md?page=2)