Cosmic Quiz: Why can’t light escape a Black Hole?

Seth Jarvis

This week’s Cosmic Quiz question comes from James Sylvester, who asks,

“If the speed of light is the highest attainable speed, why can’t it escape a black hole?”

First, a few words about the speed of light, which is indeed the fastest speed attainable through space.  How fast is it?

The speed of light is 299,792,458 meters per second.  That works out to about 186,000 miles per second.

Trying to go at or faster than light through space requires inventing exotic new mathematics that permit real number answers to equations that involve division by zero and square roots of negative numbers. If you can figure out how to do this sort of math, a Nobel prize is yours for the asking.

The speed of light is more than just a zillion times faster than we’ve ever been able to achieve with our technology, it’s also a fundamental constraint on everything – both matter and energy – in the universe.

So if nothing is faster than light, than how can a black hole “trap” light?

Light is trapped in black holes because black holes bend space itself.

All objects with mass curve the space around them.  Objects with little mass, such the Earth and Moon, only curve space a tiny amount, while objects with the mass of stars curve space a lot more. For a really massive object, like a black hole, the curvature of space they create in their vicinity is so severe that space is wrapped completely around itself.

Here’s a way to create a model of a black hole:

Take a sheet of paper.  That’s the universe.  To keep things simple, let’s declare that this is a one-dimensional universe, in that objects within this universe all exist along a single mathematical line and they can move in one direction only – left and right along that line.  In this 1-d universe there is no such thing as moving up and down on the paper, nor can you be anywhere except on the paper.

To get from the left side of the paper (we’ll call that point “A”) to the right side of the paper (we’ll call that point “B”) you have to move in a straight line on the surface of the paper.

Without massive objects being present, the 1-d universe lies completely flat, and the shortest route (indeed, the only route) between A and B is along that flat straight line.  So far so good.  The shortest path between two points in flat universe is along a straight line.

But what if you introduce a massive object, like a star, into your 1-d universe?

The mass of the star bends space itself.  You, living on the paper in this simplified universe, don’t see this curvature because your line of sight can only follow the line through space.  Seen with the benefit of having extra dimensions (as you are when you hold the paper) you see a straight line traveling on a curved piece of paper. Is the line still straight?  YES.  It’s the space itself that’s curved.

In this 1-d universe imagining a jump from A to B without following the straight line is the equivalent of imagining a science-fiction jump through “hyperspace.”

What if the object on the line of your paper is so massive that it curves space completely around on top of itself?  What if point B were inside the region where the curvature of space exceeds 360 degrees?

Then you’d have a black hole.  Traveling along a straight line from A to B (as you must in this 1-d universe) you’d encounter a place where space had wrapped around itself and once you enter this region, no matter how fast you go, even at the speed of light, you can never leave.

That’s a 1-d black hole.

Now try imagining a point in space where space itself has been curved on top of itself in all dimensions – left-right, up-down, forward-backward, and time itself.

Black holes capture light (thus making them “black”) because light is trapped within a region of infinitely inward-curving space.

The term “mind-bending” seems appropriate, don’t you think?

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35 thoughts on “Cosmic Quiz: Why can’t light escape a Black Hole?

  1. When you say the black hole doesnt let light escape, what does it do with it then? like where does it go? how do we know it doesnt end up somewhere else

    ~ Jessica Moore 16

  2. What is inside in the black hole? Should we call this thing the vacume cleaner of the space? Is there is another universe for the solar system? Why we cannot go there? Can we think in a mythology way?

  3. What is inside a black hole?

    What’s inside it is all the mass that went into making it plus whatever the black hole has eaten since it formed.

    BUT, there are no atoms inside a black hole. The components of atoms – protons, neutrons and electrons – have all been crushed out of existence and occupy an infinitely small and infinitely dense point known as a “singularity.”

    There is not a single atom of matter that we would recognize within a black hole. There’s no such thing as carbon, oxygen, iron, silicon or even so much as an atom of hydrogen in a black hole’s singularity.

    Why can’t we go there? Well, actually, you can – but you have to be willing to let the black hole kill you in a rather spectacular and gruesome manner on the way in.

    As you got close to the black hole’s event horizon your spaceship and your body would be pulled into a long, spiraling parade of atoms traveling in single file as the black hole’s immense tidal forces overcame your body’s ability to hold itself together. The molecules of your body are torn apart by the tidal forces present near a black hole. Astronomers refer to the process as “Spaghettification.”

    “Can we think in a mythology way?” Sure you can! Let your imagination run wild. Science fiction depends on people using their imagination.

    Just remember though, there are no atoms in a black hole.

  4. Just for argument sake this is all speculation though right? No proof or evidence that these are the properties of a black hole are available. Theories are not law. No man on earth has ever come close enough to a black hole to form a valid opinion on what exist within. Although I agree, and most likely this all true, we have no proof that atoms do not exist within a black hole. Science fiction theories on black holes being portals to time travel and new dimensions are honestly as believable as these. Science is fact and this is not that.

  5. Well…

    I’m going to gently take issue with a couple of the points you make.

    While it is true that no one has actually sent a probe into a black hole in a direct search for atoms (the closest black hole to Earth is about 1,600 light years distant), the nature of black holes themselves prevents such an experiment while at the same time the laws of physics pretty much make it impossible for an atom (involving a nucleus and one or more electrons occupying a discreet volume of space) to exist.

    Remember that a black hole is by definition a singularity – that is, a point with no dimensions. None. It has no width, height or breadth. It’s a mathematical point in space.

    Moreover, the tidal forces experienced by any matter just before it crosses over the edge of the event horizon all but guarantee that prior to falling beyond this ultimate point-of-no-return at a black hole no atom can hold onto its nuclear structure, let alone hang on to its electrons.

    And regarding the point you make about “theories are not law,” I don’t believe that’s a scientifically accurate statement. In science, the word “theory” means much, much more than just someone’s educated guess.

    Scientists use the term “theory” to represent an explanation that is testable, predictive, coherent, parsimonious and yet encompasses the largest available body of observable facts.

    Examples of these would be Germ Theory and the Relativity Theory. The fact that these are “theories” doesn’t mean it might be OK to eat stuff in your fridge that’s been there so long it has begun growing fur, or to doubt that atomic bombs are real.

    I hope this helps.

  6. I know this is impossible, but if you were say going faster than the speed of light, could you escape a black hole even if you were inside the event horizon?

  7. I realize that this answer may not be very satisfying.

    It would require a fundamental change to the laws of physics for any signal to travel faster than light. Such a change would also alter General Relativity. As the properties of a black hole are determined by these laws, such a major change could potentially alter those properties in significant and unexpected ways. Therefore, it would be difficult to predict what might happen under those circumstances.

  8. Around the world, research stations are trying hardronovy particle accelerator.
    This device helped by the rapid weather changes and also to create a black hole.
    It is my opinion because the storms, wind and sudden weather changes be opened for several months.
    In the past, so was not able to change the weather.
    I know that the world is tested for various things but I do not know shillings.
    This is my opinion.

  9. I can’t understand how can anyone say that a black hole has no dimension at all. I think of a black hole as a round planet with gravity pulling in toward the center from all directions evenly. As matter comes near it, it gets caught in the gravity field and slammed onto the planet. Since the gravity is so great it literally crushes everything into something beyond atoms. Then the gravity accelerates it to whatever the terminal velocity would be for that matter and slams it onto the planet surface. What’s left which is still matter becomes part of the planet itself.
    The reason light doesn’t escape is simple, point a flash light at yourself and put your hand in front of it… the same thing happens with a black hole the light gets bent to a point where u cannot see it or blocked by the planet itself.
    This thing about thinking that space folds and wraps around things is the dumbest theory i have ever heard. Space is nothingness it is not a blanket. a planet sits in space. it does not create a void or wrap space around itself. Light waves can be bent but that doesn’t mean space is bent. For brilliant people they all start to sound like quacks. The truth is there is a thin line between brilliantly smart and Madness. Hate to say it but a lot of scientist fly off the deep end.

  10. Hmmm…

    Sorry, David, but the scientific evidence doesn’t support what you’re saying.

    While a Black Hole’s Event Horizon may have dimensions, the Black Hole itself is indeed a singularity – it has no width, breadth or height. It’s a point in space with zero volume. Black Holes may grow in mass, and the size of their Event Horizons will change as their mass changes, but the Black Hole itself remains a singularity.

    “This thing about thinking that space folds and wraps around things is the dumbest theory i have ever heard.”

    The simple fact is that the gravitational curving of space is absolutely real has been observed many, many times. The phenomenon of Gravitational Lensing is a major field in observational astronomy.

    “Light waves can be bent but that doesn’t mean space is bent. ”

    Again, the scientific evidence doesn’t support that statement. Bending spacetime has been observed since 1919.

    You can use a ruler to draw a straight line on a sheet of paper, but if you then roll up the sheet of paper you’ve still got a straight line; it’s just a straight line drawn on bent space.

  11. Hi Rachel,

    The curvature of space near a black hole should not be thought of as a physical barrier to the movement of matter. Instead, think of the curvature of space near a black hole as a slope of increasing steepness that governs the behavior of matter traveling through that space.

    What follows is a huge oversimplification of the effects of mass on space, but I’m hoping it will serve for the purpose of answering your question.

    Imagine you are a rolling ball, far from the black hole, where the slope towards the singularity is still shallow. If you found yourself beginning to roll towards the black hole you could apply some energy to change the direction you’re rolling and move “uphill” from the black hole and head for flatter, safer places. Finding the energy required to leave the vicinity of the black hole at this distance is possible because the curvature of space there is mild and manageable.

    However, as you get very close to a black hole the curvature of space becomes increasingly severe, and if you found yourself close enough to the black hole to be at its “event horizon” then in order to escape you’d have to apply energy to yourself equivalent to moving you at the speed of light just so you could to stay the same distance from the black hole and not get any closer.

    Should you become unlucky enough to actually fall inside the black hole’s event horizon then the amount of energy needed to move you away from the black hole is greater than the amount of energy needed to accelerate you to the speed of light.

    Since accelerating matter to or beyond the speed of light involves physics requiring division by zero and finding non-imaginary square roots of negative numbers, you’re pretty much out of luck.

    Once inside a black hole’s event horizon, there is not enough energy in the universe to push you back out.

    It’s easy to get into a black hole, but there’s no way to get out of one.

  12. Thanks for all the info Mr. Jarvis. People that dont have expertise on subjects like these should really look at the facts or ask someone who knows before going off half cocked about how they think advanced physics works without any proof. Like Mr. Jarvis said, there are many theories that everybody accepts as fact like gravity for example.

  13. Actually, the most resonable theory for what is inside a black hole is a very very very very dense structure that is millions of times harder than a diamond and when I say unimaginable, it is literally unimaginably dense its impossible to imagine how extremely dense and heavy it is. Imagine having something so dense, that just the amount of a golf ball would be heavy enough to fall through the earth and come out the other end after miles and miles of magma and not to mention the core which is also extremely dense and have absolutely no difference in shape or size.

  14. Oh and also, explain how there isnt anything faster than the speed of light? I mean, its the fastest speed that we know of but for all we know, there could be other types of matter and completely differnt phisical laws far away beyond our current viewpoint? Seriously, what makes speed stop at light? Speed is all numbers. And like numbers, there is no limit. Correct? I must be missing something…

  15. Oh and by the way im only in 9th grade so if your laughing in your office wondering what adult is so confused and uneducated, then i’m only in high school haha.

  16. Hi Chris,

    The speed of light represents the “speed limit” of the universe because accelerating matter to or beyond that point requires an infinite amount of energy.

    Other weird things happen to you at the speed of light, too, including time stopping for you and completely losing your dimension of length in the direction of travel.

    Yes, it’s weird and unintuitive, but who said the Universe was obligated to be non-weird and intuitive to humans in the 20th & 21st Centuries?

    Study-up on something called the “Lorentz Transformations,” it’s a pretty straightforward description of what happens to length, mass and time to objects as they approach light speed.

    A nice beginning to this is to get hold of a NOVA (PBS) program called “Einstein’s Big Idea” and watch it.

  17. Chris, the “very very very very dense” matter you’re describing is the material often referred to as “neutronium” – which is the degenerate neutron corpse of certain high-mass stars that have undergone a supernova explosion as they die.

    Even a neutron star has limits to how massive it can get, and somewhere above 4 or 5 times the mass of our Sun a neutron star’s gravity is so powerful that the star itself must collapse into a zero-dimensional singularity that we know as a Black Hole.

  18. Thank you very much for the answers. Its nice to have a site where I can ask such questions without having somebody look at me like I just spoke another language! I look forward to more cosmic quiz questions!

  19. A very interesting article indeed! I’m really into this stuff. Tho I have some questions :P :

    What exact particles exist in the black hole? It’s denser than quark-gluon plasma. What exactly is denser?

    I’m still trying to figure out how exactly objects bend space. It’s all pretty simple in 1D universe but I can’t picture our 3D space being bent. Basically the object moves into the 4th dimension (like that orange ball moves down, into 2D), dragging the space around it?

    So light goes inside a black hole and just goes round and round there. Is this space bending the same like for example the Moon circling Earth?

    Can a black hole get ”unleashed”? Like there will be a big explosion pretty much like a big bang when it gets big enough?

    There was some talking that the LHC can create a black hole. Bullpoop I say. Earth itself doesn’t have enough mass for a black hole, right?

    Is that black hole image real?

    Thank you for your time! :)

  20. John,

    At the center of a black hole there is zero size and infinite density. The laws of physics are inadequate to describe these conditions, so the question of what kind of particles can exist there cannot be answered at this time.

    We cannot accurately picture space-time curvature in more than two dimensions. That is the reason one or two dimensional representations are used. However, even though we cannot picture space-time curvature in three or more dimensions, there are mathematical representations that can accurately model it.

    The event horizon of a black hole is a boundary surrounding the black hole. Inside this boundary space-time curves back in on itself, so that anything inside the boundary cannot escape, including light. So, space-time curvature inside the event horizon is not the same as that surrounding Earth and Moon. Also, black holes cannot “explode”.

    Here is a very succinct statement from the LHC website. “According to the well-established properties of gravity, described by Einstein’s relativity, it is impossible for microscopic black holes to be produced at the LHC.”
    The “black hole” image in the article is a computer simulation.

  21. For the space-time curvature to be infinite wouldn’t the density of the black hole have to be infinite to. And for the black hole to be infinitely dense wouldn’t have had to have swallowed the whole universe? or more?

    My question is it possible that light only travels a very long distance into a space curve that we cant see into but will eventually emerge out the same way it went in?

  22. Well I guess everything has changed since scientists have found particles that travel faster than the speed of light.

  23. Yes, I believe everything is energy, there are no “particles” Empty space is not empty, physicists generally agree on this. It is full of energy just like the atmosphere is full of air. Light is just one wavelength of energy that can only be transferred at it’s given speed. Scientist seem to have discovered “particles” wavelengths that can be transferred at a faster speed, I seem to remember experiments where the transfer seemed to be instantaneous. A black hole may be a gravity giant (to go back to Newtonian theory) where energy is being sucked in (possibly because of the lack of energy that the universes energy pushes to replace, therefore no transfer of light or anything else can be transferred out. This does not require the existence of a “warped” space. Just a gravity energy, again with kudos to Newton. Then why can’t light travel faster than it’s given speed when ejected by a moving object, because it can only be transferred at its given speed.In difference to Einsteins relativity theory, Time is a man made concept that takes energy to measure. Speed, moving energy “particles” faster effects the existence of the energy thus affecting our perception and measurement of time. Time doesn’t exist, there is only right now. To say 3D space warping is beyond explanation or comprehension is very unscientific and resembles religious faith. This “theory” is based on space being empty. New scientific discoveries are beginning to shoot it down. How about the “theory” where everything exists on a 2 dimensional plane and the 3d universe we perceive is just a “hologram”?

  24. I too agree that Time doesn’t physically exist.

    Personally, I’ve always thought that energy doesn’t exist either… It’s just kinda abstract. As a little kid I believed energy = something moves.

    Maybe the universe, even empty space IS filled with something. I’ve always imagined empty space as a jelly; and a wave, for example a photon, as a disturbance in that jelly.

  25. @john flammic

    sorry to disillusion you, but space cannot be related to as a “jelly”. this shows extreme 2 dimensional thinking. space is, just as @bill says, like air. it is full of stuff, and is 3d. there is an up, down, left right, up/left, up/right, down/left, own right, etc. the position is relative to you, and your state in the space around you, but it is sill the same as that on earth. theories are not generally based on fact. they are based on what we percieve to be fact. what we se is not always what is there, however. what appears to us to be a black hole, may in fact be a simple trick of observation. the fact that we think it is what we say it is, simply reminds me that we need to remember that the beginning of wisdom is to say “I do not know”

  26. After years of reading about light not escaping black holes i still do not understand why that is inevitable.
    Its not about gravity, but its apparently about the photon’s inability to overcome the increasing slope of space time near the horizon. The best I can surmise is that the ray of light is drawn to the event horizon and once that’s crossed space time beyond is so inverted/convoluted that getting out is impossible…?

  27. The curvature of spacetime inside the event horizon of a black hole is so severe that it has folded in on itself. It is essentially an endless inward spiral.

  28. Isnt the only way out of a black hole through its inevitable evaporation, particle by particle? I heard this on star talk radio a while back but may have it wrong as I cannot find the episode. Thanks for such a awesome site!

  29. I have struggled with this concept for some time now and finally think I get it. Imagine a spherical object made of hallow bicycle-like spokes protruding outward from the center similar to a dandelion flower to represent space. In normal uncurved space free from gravitation lensing light would travel along these spokes in strait line. Now imagine you put a large object with a strong gravitational pull. The spokes will bed in the direction of the gravitational object(hope that makes sense), so when light passes through the spokes the light travels straight but the spokes are curve and hence we have gravitational lensing. Now imagine the objects pull gets stronger and the spoke bend even more, and then the force becomes really strong till all the spokes have been pulled so they are all facing downward. The center of this object represents what happens at the event horizon.

  30. What’s on the other side of a black hole? A “white” hole, forming another universe? Nothing comes from nothing, so nothing can be smeared (or in this case, crushed) out of existence, because energy cannot be created or destroyed, only transferred. With this being said, can everything being crushed into oblivion be “born” in spontaneity somewhere else?