We've all been told that nothing can escape a black hole, not even light. Our teachers told us so, our books told us so, and now even documentaries are talking about black holes; always pointing out to us that even light will get sucked into black holes.
The basic premise of a black hole is fairly simple. A giant star builds up so much mass that it literally gets sucked into itself by the sheer amount of gravity it produces. We all know on an elementary level how gravity works. So it's easy to understand why objects passing by get sucked into black holes. On the other hand, we've always been taught that light is not matter and therefore not affected by gravity. Earth has gravity after all, and yet if you turn on a flashlight, the light doesn't eventually fall to the ground. So what makes black holes so special that their gravity can suck light in, never letting it go?
Black Holes and Spacetime
In order to understand why light gets sucked into black holes, it is first important to understand a few particular traits of the black hole.
As you may know, everything with mass has gravity. The more mass an object has, the more gravity it has. This is why the planets revolve around the sun, and not vice-versa. But contrary to what you may think, gravity is not the key component in a black hole's ability to trap light. The real culprit is the mass of a black hole, and its effects on spacetime. (Also referred to as spacetime or space-time)
Everything that has mass causes the spacetime around it to bend. More mass creates a larger bend in spacetime. To explain, imagine an empty trampoline sitting in your back yard. This is what space time would look like if there were no mass to distort it, except that space has three dimensions, not just two. Now put a bowling ball on top of the trampoline. That heavy ball creates a distortion in your trampoline. This distortion is exactly what happens in space wherever mass can be found. To make things far more complicated, black holes take this to the extreme. At the event horizon of a black hole, space time actually bends into itself!
The Shortest Distance Between Two Points
As a rule, light will always travel the shortest distance between two points. Here is a mind-bender for you: The shortest distance between two points is not always a straight line. Yes, your elementary teachers lied to you. Take that home, chew on it for a while.
The truth is, the straight line theory only works in two-dimensional space such as on a piece of paper. On a curved surface, this is not the case. Real life examples of this are actually in use on a daily basis. If you look at the figure to the right, this is the plot for an airline flight with no layovers from Seattle to London. One would normally assume that this flight would just cross over the US passing through Maine, then right over the Atlantic Ocean. Since Earth is spherical, however, taking that path would actually be far longer than the path depicted. (Check out other flight paths here) This is known in aviation as the great circle.
Black Holes and Light
Now that you are armed with the necessary information about how light travels, and how black holes bend spacetime, you can begin to understand why light will get sucked into black holes. Just like a plane using the curvature of the earth to travel between two points, light will follow the curvature of a warped spacetime, in order to get from origin to destination. This can be seen whenever light travels past a massive object. The light appears to bend. But on the contrary, it is spacetime itself that is bending, not the light.
When light travels into a black hole it will eventually hit the event horizon, and as spacetime continues to bend into itself; the light will follow. So really, light will never get sucked into black holes. Instead, light is simply following its normal behavior, and traveling straight into black holes on its own!
Jeff on March 16, 2020:
This is as wrong as a fish in a volcano
Dd on June 04, 2018:
The example with the plane's path from London to Seattle is misleading, the only reason the line is not straight on a 2D surface is because of the method used to project a 3D sphere onto a fat surface. If you were to look at it on Google Earth, the shortest path is still a straight line.
Akbar Hussain on April 19, 2018:
Wonderful mind-boggling information. Like it. Appreciate it. Learned a few new things. Feeling happy and satisfied.
Maria Janta-Cooper from UK on January 04, 2013:
Great article. Thanks for writing it. Nice explanation; however, a photon is not a plane :-) I don't understand why a photon has to follow the curvature of space time. Is it not possible for light to travel not along of space time but square to it? Probably it would work against all the laws of physics.
sgsamgise on November 26, 2011:
Yeah, the brick theory sounds hard to believe (even I don't believe completely, but read on) because it seems to imply "fate" or something like that (which of course is out of topic), but it makes "some" sense if you take into account that everything in the universe is only information, matter and events are only information, mathematical results of the laws that rule our universe. With that in mind, the event "brick falling in your head" (like any other event that could prevent you from changing the past) might just be the mathematical result of an ecuation that is derived from the underlaying nature of the Universe: "past and present must be coherent", and so the Universe finds a mathematical result (a result that was most likely a possiblilty since the beginning of events) that allows the system to remain congruent.
It's something really hard to grasp, I mean, understanding that the event "brick on your head" is not something that the Universe chose to happen just like that, but it was just the Universe reacting to the change in the physical variables you made to the system by travelling past, and responding with a change in the ecuation that nullifies those changes. The result might be anything that maintains coherence in the system.
Even I (the one proposing this theory) have problems imaging how a mathematical ecuation can result in a brick in my head, but maybe this underlaying mathematical coherence is the one that makes the results of the ecuations of the laws to be logical (and prevent physical absurds like a proton just dissapearing with no reason).
Have I just found the sicientific explanation of coincidences??
Hehe of course not, anyway, this are just my ideas (some come from the book "The Elegant Universe" by Brian Greene, one of the best books in the field), and I prefer to believe that we just can't travel past in the same timeline, it's easier and avoids the brick in the head :)
Steven Pearson (author) from Bonney Lake, WA on November 26, 2011:
See, while I know something has to prevent you from killing your own grandfather - I never really supported the "brick" theory. I would be hard pressed to believe that just because you went back in time, all of a sudden a brick falls on your head, or you just "change your mind" (which eliminates the idea of free will) or things like that.
However, something like a black hole, which is already twisting the hell out of space time...now that's something I can see possible.
The different time lines, a la "alternate universe" however is a bit more believable. But that I think is a form of physics we are still a long ways away from.
sgsamgise on November 25, 2011:
Me again :) @mattforte "black holes are simply nature's way of preventing backwards time travel". That's something very interesting which some scientists also think, that, in order to prevent paradoxes or physical absurds, the Universe has a way of collapsing wormholes before an exchange of information between two different times/eras can occur. Or, in the case it occurs, the Universe would find a way to prevent this from affecting the coherence of the timeline and creating a paradox.
An easier to say this is by the use of the ancestor's paradox: If you tried to go back in time to kill your ancestor (which would prevent you from being born and therefore making impossible for you to go back in time to kill him), the Universe would either prevent you from traveling to the past in the first place (by collapsing the wormhole) or, in the case you actually go to the past, "something" would happen (like a brick falling on your head) that would prevent you from killing your ancestor or doing anything that could affect the future in such a way that could prevent you from traveling back in the first place.
BUT, that only happens if there's only ONE timeline (in which case, as being the only one, it must be coherent and paradoxes cannot exist), but I'm in the group of people that believe that every time you travel to the past you end up in a different timeline, so that it doesn't matter what you do there, your previous timeline is not affected (but you can't go back to it anyway).
Ufff this comment has got very long, I think your last comment hit a sweetspot, better leave it here!
Steven Pearson (author) from Bonney Lake, WA on November 25, 2011:
Thanks Beata. I'm really not that good at it, I just put up a good front ;-)
Lumarie: I've seen a few physicists in documentaries try to come up with calculations to possibly prove backwards time travel possible, and it seems like when they come up with something that could work, it instead creates a black hole. As if, bending space time to the point where backwards time travel is possible, the black hole gets created as a result...which I think might just show that black holes are simply nature's way of preventing backwards time travel.
I have lots of thoughts on that subject as well, just spouting out I guess haha.
lumarie from Puerto Rico on November 25, 2011:
Yes, I LIKED IT. mY STORY THAT i AM WRITNG has to do with time travel, and I talk about a wormhole.
Beata Stasak from Western Australia on November 25, 2011:
Great hub...love science and admire people who are good at it...(as I am not:)
Steven Pearson (author) from Bonney Lake, WA on November 24, 2011:
Thanks! Getting a compliment like that from a science teacher of all people is a confidence booster!
talitz2550 from Thailand on November 24, 2011:
I was drawn to this first I'm a Science teacher, second, anything about space entices me.
This hub is interesting. I love the "shortest distance" part. Very well done congrats. :)
Steven Pearson (author) from Bonney Lake, WA on November 24, 2011:
I love it! Definitely not dumb, the fact that you can even do that math proves otherwise. And that just goes to show, you were destined to read my hub!
Thanks! I think a lot of times when you get into astrophysics and such, things are explained in such a way that most people really can't understand. When you get into crazy things like black holes, even the "simple" explanations tend to make heads explode (I know this, my girlfriend always tells me her head is exploding) so I think a good metaphor is a wonderful thing!
John MacNab from the banks of the St. Lawrence on November 24, 2011:
I love your descriptions mattforte. A very interesting and informative hub. I especially like your trampoline and flashlight descriptions. Thank you.
sgsamgise on November 23, 2011:
Interesting, I thought light was actually affected by gravity, only very little, it hadn't occurred to me that light was just following the bent space around stars (an other heavy objects). Now that I think about it, I feel a bit dumb because I already knew light has no mass so I should have known it's not affected by gravity (at least not in the conventional way F = G(m1*m1)/d2).
And a funny thing, this morning I woke up from a dream about black holes (I was creating a baby one one in my house and it was out of control, how crazy), then when I get up I turn on the TV and the first thing I see is a documentary about black holes in the History Channel, and now I check in my email my Hubpages Weekly and I see this Hub about black holes, what are the chances?? o.O
Anyway nice concise hub!
Michelle Simtoco from Cebu, Philippines on November 20, 2011:
As a child, the concept of a black hole was frightening...now it has become interesting! Hmmmmm...
Congratulations mattforte on your Hubnuggets nomination. There is no black hole in this hub just full of nominees and the chance to be in the Hubnuggets newsletter! Follow me as you read and vote, https://koffeeklatchgals.hubpages.com/hubnuggets6/...
Steven Pearson (author) from Bonney Lake, WA on November 20, 2011:
Haha, yes black holes bend minds as well as light ;-)
Mary Hyatt from Florida on November 19, 2011:
I don't pretend to understand all this, but I enjoyed reading about it. Interesting Hub.
Lisa from WA on October 30, 2011:
Very fascinating hub! This stuff always loses me but u were very concise and easy to read