Physicist: A black hole is usually described as a singularity, where all the mass is (or isn’t?), which is surrounded by an “event horizon”. The event horizon is the “altitude” at which the escape velocity is the speed of light, so nothing can escape. But if gravity is “emitted” by black holes, then how does that “gravity signal” get out? The short answer is that gravity isn’t “emitted” by matter. Instead, it’s a property of the spacetime near matter and energy.
It’s worth stepping back and considering where our understanding of black holes, and where all of our predictions about their behavior, comes from. Ultimately our understanding of black holes, as well as all of our predictions for their bizarre behavior, stems from the math we use to describe them. The extremely short answer to this question is: the math says nothing can escape, and that the gravity doesn’t “escape” so much as it “persists”. No problem.
Einstein’s whole thing was considering the results of experiments at face value. When test after test always showed the speed of light was exactly the same, regardless of how the experiment was moving, Einstein said “hey, what if the speed of light is always the same regardless of how you’re moving?”. Genius. There’s special relativity.
It also turns out that no experiment can tell the difference between floating motionless in deep space and accelerating under the pull of gravity (when you fall you’re weightless). Einstein’s stunning insight (paraphrased) was “dudes! What if there’s no difference between falling and floating?”. Amazing stuff.
Sarcasm aside, what was genuinely impressive was the effort it took to turn those singsong statements into useful math. After a decade of work, and buckets of differential geometry (needed to deal with messed up coordinate systems like the surface of Earth, or worse, curved spacetime) the “Einstein Field Equations” were eventually derived, and presumably named after Einstein’s inspiration: the infamous Professor Field.
This is technically 16 equations (μ and ν are indices that take on 4 values each), however there are tricks to get that down to a more sedate 6 equations.
The left side of this horrible mess describes the shape of spacetime and relates it to the right side, which describes the amount of matter and energy (doesn’t particularly matter which) present. This equation is based on two principles: “matter and energy make gravity… somehow” and “when you don’t feel a push or pull in any direction, then you’re moving in a straight line”. That push or pull is defined as what an accelerometer would measure. So satellites are not accelerating because they’re always in free-fall, whereas you are accelerating right now because if you hold an accelerometer it will read 9.8m/s2 (1 standard Earth gravity). Isn’t that weird? The path of a freely falling object (even an orbiting object) is a straight line through a non-flat spacetime.
Moving past the mind-bending weirdness; this equation, and all of the mathematical mechanisms of relativity, work perfectly for every prediction that we’ve been able to test. So experimental investigation has given General Relativity a ringing endorsement. It’s not used/taught/believed merely because it’s pretty, but because it works.
Importantly, the curvature described isn’t merely dependent on the presence of “stuff”, but on the curvature of the spacetime nearby. Instead of being emitted from some distant source, gravity is a property of the space you inhabit right now, right where you are. This is the important point that the “bowling ball on a sheet” demonstration is trying to get across.
The Einstein Field Equations describe the stretching of spacetime as being caused both by the presence of matter and also by the curvature of nearby spacetime. Gravity doesn’t “reach out” any more than the metal ball in the middle is.
So here’s the point. Gravity is just a question of the “shape” of spacetime. That’s affected by matter and energy, but it’s also affected by the shape of spacetime nearby. If you’re far away from a star (or anything else really) the gravity you experience doesn’t come directly that star, but from the patch of space you’re sitting in. It turns out that if that star gets smaller and keeps the same mass, that the shape of the space you’re in stays about the same (as long as you stay the same distance away, the density of an object isn’t relevant to its gravity). Even if that object collapses into a black hole, the gravity field around it stays about the same; the shape of the spacetime is stable and perfectly happy to stay the way it is, even when the matter that originally gave rise to it is doing goofy stuff like being a black hole.
This stuff is really difficult / nigh impossible to grok directly. All we’ve really got are the experiments and observations, which led to a couple simple statements, which led to some nasty math, which led to some surprising predictions (including those concerning black holes), which so far have held up to all of the observations of known black holes that we can do (which is difficult because they’re dark, tiny, and the closest is around 8,000 light years away, which is not walking-distance). That said: the math comes before understanding, and the math doesn’t come easy.
It’s funny because it’s true.
Here’s the bad news. In physics we’ve got lots of math, which is nice, but no math should really be trusted to predict reality without lots of tests and verification and experiment (ultimately that’s where physics comes from in the first place). Unfortunately no information ever escapes from beyond the event horizon. So while we’ve got lots of tests that can check the nature of gravity outside of the horizon (the gravity here on Earth behaves in the same way that gravity well above the horizon behaves), we have no way even in theory to investigate the interior of the event horizon. The existence of singularities, and what’s going on in those extreme scenarios in general, may be a mystery forever. Maybe.
This probably doesn’t need to be mentioned, but the comic is from xkcd.
a similar question, does a black hole have an electric / magnetic field? can the field escape the horizon and manifest outside the black hole?
what about a photon attempting to escape the black hole moving perfectly ‘up’ against gravity (assuming a static, uncharged black hole), could it escape the horizon just by moving perfectly straight away from the singularity?
@Xerenarcy
Black holes can definitely have some charge and have associated electromagnetic fields. Turns out that the idea is about the same as the gravity field. The conservation of charge can be expressed in a number of ways, including in terms of the “conservation of the electric field” (in a particular sense).
I’ve read that gravitational waves propagate at the speed of light. If that’s true, is there any particular reason a property of space time fabric feels the need to limit itself to that velocity? What gives?
Black Holes are amazing and entropy of Black Holes also is an interesting topic. It always made me dream about what lies “beyond” the event horizon, within the singularity itself….does it spit matter into another “Universe”? Speculations of course, but what cannot be denied is that Black Holes are and may continue for a while to form one of the “darkest” mysteries of our physical Universe…
We need first to understand what hapens on the smal scale!I sugest u look into “cold fusion”.
You cannot measure the inside of a black hole, as nothing exist there not even time, externally its diameter can be measured as time exists. If a gravitational force is being measured from the black hole, the exact same measurement would exist on its opposing side. Jacktar.
So for gravity waves, which have recently been confirmed in the cosmic background, ‘ripples’ moving in the space-time geometry? The rubber sheet analogy suggest that the curved space-time geometry is static but as all bodies emit energy then the gravitational field around a body must decrease continuously ( though negligible). Is this what the ‘ripples’ are?
@ Niko D
The speed of light is built into the nature of the universe. The fact that it’s called “light speed” is just an unfortunate result of light being the first thing we studied that involved that speed. We see the constant, C, showing up all over the place in the study of space. For example, in the spacetime interval, which is the most basic notion of “distance” in spacetime.
@LarryD
You can think of gravity waves as being similar to the effect of moving a mass back and forth on the rubber sheet. If it moves back and forth fast enough, you’ll find waves propagating away from it. We don’t expect a stationary object to emit gravity waves, but we do expect things like tight binary neutron stars will be a decent source (lots of mass moving back and forth very fast).
I think article is a little bit inconsistent. First you tell that gravity is special, than you tell, that electric and magnetic fields can also escape, because they are also are “property of space and time”. What it does not tell is why light won’t escape than.
I’d propose different much simpler explanatio:. What if whenever something hits event horizon, it becomes part of event horizon (e.g. event horizon fluctuations)? That would explain why gravity, light, and Hawking’s radiation can “escape” the black hole – because there’s no “hole” behind a horizon, just a horizon, which can emit and consume particles and fields.
@Flavian Pop
The definition of a universe suggests that anything which is outside of the universe must be unable to interact with it’s physical existence. By this definition, a Black Hole can not quite be it’s own universe. Although a large many things on the inside can not be measured, One thing that can be measured is mass, by means of it’s gravitational pull. Likewise, the contents of a black hole can also be altered by the outside, by means of incoming matter, energy, and gravitational forces. Since both sides can communicate with one another, and information can be transferred between the inside and outside of the event horizon, they are defined as being within the same universe nonetheless.
@The Physicist
Using a rubber analogy is kinda weird though, isn’t it? It draws back to the ether days of light theories. It’s almost like we’re attributing the speed of light to being similar to a sound wave, but through the medium of space-time. Granted, we DO find the speed of light showing up almost everywhere, even when studying binary star systems – the actual gravitational attraction of one star to the other isn’t actually directly towards the other, but rather towards where the other star WAS approximately r/c time ago (r being the distance between the two stars). That’s pretty much conclusive evidence that gravity travels at the speed of light.
In our theories that means the spacetime ripples undulate at that speed. If other fields (like the electric and magnetic fields) also move at that speed then you can tie those two together and say that the fabric of space-time also has electric and magnetic field components, but with how DIFFERENT they are from gravity, it’s hard to imagine where they are in that realm. Light (photons) are obviously “attracted” gravitationally, but in a much different manner from matter, which is directly subject to this gravitational force. They propagate by means of a changing electric field which produces a changing magnetic field and so on…so if you for a moment say that those fields follow the structure of the GRAVITATIONALLY bent spacetime, it makes sense that they bend towards pockets.
What doesn’t seem to make sense is how a black hole, with a singularity at its center, can still emit EM radiation. Those electric fields must propagate through a region of spacetime in a way that doesn’t lead to them bending back into the center. If they do that in a way that’s not subject to the basic description of light, then we need a better field theory that includes electric and magnetic fields within the same bending of space-time as general relativity.
I know there may be some glaring “what, no” in there, lol. I’m only just now getting into physics so if I’m totally getting some theoretical understandings wrong just let me know 😛
@Static
The rubber analogy is terrible (for the type of reasons you point out), but it’s usually the best we have. Physicists don’t use it for understanding (that’s what the math is for), just for explaining.
While a black hole can have charge and an electric field, that’s different from emitting radiation. We usually hear about the EM force as being “mediated by photons”, which it is, but the process is a lot more subtle than firing photons back and forth. Quantum physics is nasty stuff.
@The Physicist
I’ve done some reading and I have run into the analogy of things like virtual photons and how from that idea we moved on to other force-carrying bosons out there for the weak, strong, and even gravitational force. I’ve done some research on it on my own but don’t really have a good understanding of WHY this model has been adopted. It also hasn’t been covered in my physics classes yet.
Only recently have I gotten into quantum physics and…it’s definitely not exactly what I expected, haha. It doesn’t surprise me that I’m gonna run into some very strange consequences of these few wave equations, and that most of those won’t really be describable using everyday comparisons XD
@Static
by far the most effective way to think / visualize spacetime is as a flow / flux. ie, it is more helpful to think of space itself falling into a black hole, and think of any photons as ‘swimming up a waterfall’ – even though they can’t escape, they are definitely trying to at (local) speed c.
@Victor, think that answers your question as well – photons can’t escape because they’re basically ‘swimming against the current’, and the ‘current’ of spacetime is what we understand to be gravitation.
the whole black hole has an electric field thing confuses me too (see above), but reading into it you do need to use some mind-bending properties of virtual particles to pull this off (describing the interaction with a particle model rather than a field model). specifically, a virtual photon doesn’t have to obey the speed of light. this sounds wrong but in fact that is what happens – due to position uncertainty a photon can span a length of space for an instant shorter than the time it would take a photon to cross said length (if i’m interpreting this correctly, please let me know if this is wrong or if there is a better explanation), which allows changes in the field internally to make their way outside the hole (just like gravity can escape due to ‘tension’ of spacetime).
it may surprise you (did me) that this does does not break causality for reasons similar to entanglement. ie, the virtual photons just do the task of mediating the electromagnetic force locally, they don’t transmit information themselves (only enforce a correlation), so there is no causality breaking here despite some sort of FTL obviously going on in the intermediate process.
that said QED is a very difficult topic. eg, explaining how a photon exchange yields an attractive force takes a lot of analogies and a lot of math, and that’s the simplified version… i dare say that warrants its own post…
and all this is before you start looking into the nightmarish solutions for a rotating / charged / both black hole, which due to the pure-math nature of the solutions (such as space flowing in opposite directions at the same time), leads people to believe in black holes leading to alternate universes and the like… fascinating stuff though.
How do you reconcile this with the (supposed) existence of graviton? Does graviton interact with black hole? Is it generated by it?
Also, how can a photon escape a massive star but not when that star finally becomes a black hole, since you say the density of an object isn’t relevant to its gravity?
@John Michaels
“Second quantization”, which is basically where particles show up, takes the field as fundamental and the properties of the particle as derived (not the other way around). That is; you write down the description of the field first, and derive the properties of the particles from it, as opposed to figuring out how the field behaves based on the behavior of the particles that compose that field.
The “density is independent of gravity” is only true at a fixed distance. So the Earth would continue to orbit in very much the same way, even if the Sun were to collapse into a neutron star or black hole (with the same mass).
> This probably doesn’t need to be mentioned, but the comic is from xkcd.
ehe, hate to be ‘that guy’ but actually, it *does* need to be mentioned according to the CC-BY-NC license that xkcd uses: http://xkcd.com/license.html
A slighty OfT question;but what would happen if you attached any random object to a highly flexible,extremely sturdy (essentially untearable) and sufficiently long rope and dropped it into a black hole?
Would you,after it has fallen beyond the event horizon,be cabale of pulling it out again(assuming that the roped hasn’t been severed),or would the force required to do so be infinitely large?If the black hole would attempt to oull the rest of the rope into it,would you be able to prevent it from doing it?
I guess you’re trying to imagine an ‘unstoppable force meets unbreakable shield’ scenario. In this case however, the event horizon is the unstoppable pair of scissors, and your rope, no matter what it’s made of (even neutron-star material), won’t be able to withstand the cut of gravity.
Even if you rope somehow makes it to the event horizon, that is the end for it. To see why, see the rope for what it is – a collection of atoms, bound to their neighbours via electromagnetic forces. What conveys that force? Photons, which are limited by the speed of light. Once the rope crosses the even horizon, the atoms of the rope that did, can no longer attract, or be attracted by, any other atoms. In fact they wouldn’t be atoms any more, since the nucleus and electrons can’t attract each other…and for that matter, the nucleus itself can’t hold itself together either (pesky forces, all limited by the speed of light).
In other words – any part of the rope that crosses the event horizon is disintegrated. It doesn’t matter what the rope is made of, even anti-matter. There is no material in this universe, which can survive.
Friction within a black hole does not exist nor does mass or time. The force used on the Rope to enter the black hole would be the same force required to pull it out, what you will notice is the temperature of the rope will now be zero degrees. Jacktar.
You say information never escapes a black hole – but didn’t hawking lose a bet over exactly that?
Or am I mistaken.
Long long ago humans thought the earth was flat, and this is where we are if “gravity “exist within a black hole. Probabilities of the universe, such as dark matter dark energy will lead to better understanding of these forces. If you apply logic to quantum theories then there can be no gravity within a black hole. Neutron particles change to a energy Particle, axion, its energy field adds to the existing chameleon force, which exists throughout the universe. This is the barrier time cannot penetrate. To get to where I am requires a lot of thinking out of the “box”. Jacktar.
what happens to the momentum of an object which falls into a black hole.
can a black hole spin.
does a spinning black hole become heavier if the matter inside is spinning at near C
Can a spinning black hole tear itself apart?
If gravity is simply a result of the geometry of spacetime, how can it also be a “force” which is mediated by a quanta (graviton)? Isn’t gravity more a “situation” or a ‘circumstance” rather than a “something?” Could this be why some very smart people has of yet been unable to reconcile QM & GR?
note web site a work in progress, kinda mishmashy right now, mixed with good intent.
question, if the lensing of light in a spiral of pluses and minuses when “lensed” through a group of galaxies, or other large body of gravity.
will the pattern of “age” of light, as revealed by spectrum analysis, vs the calculated difference in the distance travelled by the light, show that light relative to other light from the same source, has travelled at different speeds, thus dispelling the myth of time dilation, and revealing a “helical, pulsating, flow to gravity, showing that light “acts” as thought flowing in a “medium” whether one is there or not.
Or maybe more succinctly,
Would undulating “age” of light, as lensed by gravity, reveal a difference in relative speeds of light, between the two paths??
just to clarify something, matter falling into a black hole – would it not heat up from the radiation bath of light from the universe being sucked in behind any matter?
also the question of a ‘rope leading into a black hole’ scenario… it is actually a very interesting case of bells spaceship paradox: two spaceships with a rope tied tight from nose of one to tail of another; suppose they accelerate at the same time, which is open to interpretation, what happens to the rope – does it compress, does it stretch, does it break, can it stay perfectly taught under some circumstance… and even then some of the best minds can’t seem to agree on the reasons even if they agree on the effects.
the important thing to keep in mind is that from the point of view of anything just crossing the horizon, nothing seems out of the ordinary per se – from the point of view of a section of rope at the horizon (assuming at an instant in time for simplicity) the rope should still be whole up until the point where tidal forces rip it apart. i have to stress that point because for larger holes the horizon is considerably larger in radius than the point where the gravitational gradient becomes strong enough to rip apart matter. basically the result depends on the size of the black hole as to whether the rope will tear before it reaches the horizon, though it doesn’t improve prospects for pulling anything out. just an interesting point to consider.
on that note, a black hole does in fact have a rotational limit. actually, if a black hole spins too fast or has a sufficiently large charge-to-mass ratio, it won’t be a black hole. a side note is that this is (amongst other things) one reason why an electron is not a black hole despite having the necessary energy density (i’m assuming this to be the case, can’t recall, feel free to correct me here). however the rotational limit is actually not as big as you might think.
and yes, a black hole has to have angular momentum conserved like anything else – things falling in contribute their angular momentum in some way (by definition the hole would inherit the angular momentum of when it was a star), not terribly important how it happens though.
regarding the graviton, the more i read into it the less likely it seems that there is such a thing as a graviton. (unrealted; to physicist: which would be weaker, a neutrino rest mass, a low energy photon or a ‘typical’ graviton? these tiny quantities are hard to compare).
having a graviton in the picture seems to go against the intuition that spacetime is smooth, and in some ways seems redundant given that gravitation is associated with energy of all types. it is a very loose argument saying that if there is a mechanism that gives rise to mass (say higgs), that this same mechanism ought to explain gravitation and the nature of energy itself (in that energy and mass are inexplicably equivalent, if it looks like a duck and quacks like a duck…).
but all that mess aside… followup to my first question regarding charge awareness past the event horizon…
indeed, there are at least two arguments for charges inside, to be felt outside a black hole:
1. charge can’t be destroyed; the total electric field of the star, by virtue of it existing in the past, it continues to exist after the star collapsed into a hole.
2. virtual particles (photons in this case) are offshell and don’t obey the usual rules, even that of lightspeed. so long as no information is transmitted faster than light (like EPR situation) this is allowed.
but this seems to raise a paradox, or i’m misunderstanding something… in order to feel the charge outside the hole, information about that charge has to be carried away in some way. even if the virtual photons can escape, the information they carry cannot by definition escape faster than light. this is still resolved by method #1 when talking about the charge of a black hole itself, but does this hold up for a charge falling into a black hole?
to restate this, could we determine the location of a charge via electric field alone, as it crosses and even after it crosses the event horizon (but clearly not before it is destroyed by the singularity), and why could/couldn’t we?
a simpler version of the same – if i move an electric charge on the moon, will this change be felt on the earth one second later? intuitively it should but given that virtual photons don’t obey lightspeed limits, how do we prove causality isn’t broken in the QED approach? i remember mention of advance and retarding waves that balance out to show information moving at lightspeed or slower but i can’t recall the details.
and a related followup question, forgive it begging the question… with respect to spacetime curvature, does the electric field follow the curvature? a (likely wrong) different way of asking this is, can we use gravitational lensing to change the shape of electric fields?
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With an escape velocity of c at the Schwarzschild radius doesn’t that imply that a black hole of finite energy binds particles of matter with infinite energy?
@Greg Marlow
It’s not an issue that comes up. Light moves at light speed (but it certainly doesn’t have infinite energy) and particles with mass can have any finite amount of kinetic energy, but not infinite (the energy has to come from somewhere).
In short, the gravitational field is set up before the collapse to this quantum object and not after.
Gravity is not particulate. It is space-time curvature.
According to stephen hawkins… in his previous theory.. it was concluded that black hole
Is rotating around an axis.. and if being watched from different sites or views.. then the seens captured are different… although it is not possible.. how can the law of gravity be applied to black hole ?? If there is gravity then every body should pass through it.. and if there is not a gravity.. then how can different views of objects can be observed.. ?? According to einstein.. gravity performs same actions almost everywhere.. then why stephen hawkins is continuously trying to prove that black hple exists.. if it exists.. then do it really behaves like earth.. and tested on the objects.. the views can be different !!!!
Gravity “acts” like it travels instantaneously.
Relativity treats gravity differently then it does light changing it mathematically as it travels so when it arrives somewhere it is as if it made the trip instantaneously in that “gravity has no time delay”.
An example of this is that the visual light image of the sun is 8 minutes behind the
gravitational pull direction. So the gravitational pull of the Sun is within experimental texting accuracy of where the Sun “really” is.
Binary (two orbiting) black holes give off energy decaying their orbits but the orbits do not decay fast enough to comply with the gravity fields attraction direction misaligning.
In other words the black holes transfer information the same way the Earth and Sun do without a measurable positional time delay.
If you consider a binary black hole system with black holes moving with respect to each other information can not be “frozen” on the surface of the black holes because as the black holes move the directional information is constantly updated.
Scraping time delayed information from the “almost” surface of a black hole does not allow enough time for this transfer of gravity directional information.
This is not intended as a criticism of relativity in any way because the equations work and there is no more you can expect from equations.
Everyone should understand that gravity and light are not the same.
Duordi
@Duane Eddy
The effect of gravity, like everything else, is limited by the speed of light. The Sun we’re orbiting is the Sun we see (from about 8 minutes ago).
Yes, and if the sun vanished (please don’t ask my how) the Earth would continue orbing for another 8 minutes around where the Sun really is.
Umm…
I feel like the guy in your stick comic.
Here is a reference:
http://math.ucr.edu/home/baez/physics/Relativity/GR/grav_speed.html
In general relativity (in the weak limit) the “force” of gravity on Earth does not point where to where the Sun is but is offset based on the velocity of the Sun.
This offset almost exactly cancels retardation (8 minute light delay) causing gravity to point at the actual location of the Sun.
This gives the “illusion” (illusion means not real) that Gravity is instantaneous as GR resolves in the weak limit to the newtonain equation which holds gravity as instantaneous.
So in GR we include the velocity of the source into gravitational propagation.
but we do not include velocity of the source into light propagation which is why the light image of the Sun is 8 minutes behind the “gravitational force vector”.
Considering the Sun Earth system was this hard I give up on the Black hole thing.
Duordi
I have heard that the calculated magnetic field of a hole is proportional to its gravitational pull, if spacetime is (sorry for the redundence) analogous to a rubber membrane and this correlation holds true.. then perhaps magnetism can be described as the gaps in the molecular structure of said membrane.
And traditional magnets only dilate those gaps without changing the shape of the membrane..
Went a bit deep in that analogy, hope you understand what I mean. Reality May have a few extra spatial dimensions that only apply to the world of the quanta.. Happy pondering..
I have many other opinions about physics that as far as my personal research has gone are hard to debate due to our lack of fundamental understanding. Feel free to contact me, kigamisama@gmail.com
If a mass crosses the event horizon into a rotating black hole will the rotational speed of the black hole increase as the mass falls towards the central singularity, thus providing information from within the black hole for example the transit time to the singularity,
may be black hole is nothing but a intersection point of event horizon…..that’s why nasa observed thousands of black holes…..
may be event horizon is the place of time modulation…..then may be black hole is not going to harm us…
Fantastic question. Thank you. Gamma rays escape from black holes, not “nothing”.
Whether gravity is a particle or a wave is answered here by the question. Gravity is neither a particle or a wave and more “sensitive” equipment will, therefore, not detect it as such. Gravity does not travel and is not a part of the electromagnetic spectrum. If gravity were a traveling force it would cease to have any effect because it would be dissipating it’s force by moving away from the object that created it, thus being a push, not a pull. Gravity exists in all mass because of the action of electron rotation around a proton or neutron. This rotation creates in each atom a force which has it’s own frequency of attraction, but in reality is detected by all other atoms through any vibrational attraction. Since the action of atoms do not have a decaying electron activity, the universe will never “run down” because it needs nothing to sustain it. Each individual atom therefore is able to “see” every other atom in the infinite universe and is aware all other such solid mass. This is now being realized by observing instantaneous “quantum entanglement”, the currently acceptable scientific term for ESP. Not being a force which takes “time” to travel means that gravity is felt instantly, everywhere. This has been proven by quantum entanglement and was first recognized by Isaac Newton, who has recently been ridiculed by many modern scientists. It was also seen by Einstein, who called it “spooky action”. The action of gravity being instantaneous has been proven by mathematical models of the solar system, and in spite of this is still being resisted.
As long as misconceptions about the universe being limited, big bang theory and gravity continue science will maintain it’s plodding course to nowhere.
I’ve been kicking around ideas and questions about spacetime and consequently black holes for a while now. The big question I’ve been trying to understand for a while now is, what IS spacetime? What is it’s essence, what is it made of? That led me to other questions such as does spacetime flow in a gravity field and take mass along with it? Is it like an infinitely mutable fabric of some sort that can be expanded and compressed from a point? I realize that what we have to work with is just math and that the math works. Is it even possible to understand the underlying reality?
Musing about this has led me to another question. The speed of light being the maximum possible through spacetime, what sort of velocity would an object dropped into a supermassive black hole obtain? Enough that time would stop for it (similar to how a photo at the speed of light doesn’t experience time)? My understanding is that an object reaches a black hole’s event horizon time stops from the perspective of an outside observer and it would simply redshift and then disappear. Does that imply that it had reached it’s maximum velocity through space and thus had no more velocity available through the time vector?
I like to watch YouTube videos about Einsteinian physics. Most of the basics are covered in many different videos. But as I look for the answers of other questions that the basics have led me to it becomes much more difficult to find anything. When searching for the effect of accelerating frames, for example, I have found very little. The same thing applies to the questions of what is spacetime and what are the effects of time in a black hole (beyond the basic fact that it slows). I found one web site from an institution of higher learning that says time and space reverse roles beyond the event horizon, i.e. one can only move through space in one direction but can move in more than one direction through time. I guess that in such a case there would be no problems with causality since we can’t see anything beyond the event horizon.
Anything you can offer to help enlighten me would be greatly appreciated.
To my comprehension, gravity is a consequence of the “deformation” of the geometry of space-time.
This deformation doesn’t really look “at all” like a ball on a sheet. This analogy only tries to explain the mouvement of an object in a space-time déformation. Reality is that the geometrical deformation is expressed at the level of the metric of space-time; and it doesn’t really give movement to objects; but it could add speed to it. Absolute “rest” doesn’t exist which means everything is moving regardless of the referential. Objects have their proper movement.
Expansion grows the metric of the universe, while mass energy (and not matter) stables that metric (stops de growth); and if you add more mass energy to an object (by adding matter particles that contains mass energy), this addition of mas energy can collapse the metric of the space-time occupied by, and around, the object, to the point of a singularity. The movement of colapsing is the contrary of the one of expansding.
So that when the colapsing of space-time reaches the singularity, which is the smallest metric possible of space-time (10^-35 meter), you get a black hole. It would be more proper to use the term “black ball” because we’re tlaking of a “volume” of space-time that colapses and not of a hole in space-time.
The mass energy I’m talking about is the kinetic energy “confined” inside a proton that gives 99% of its mass.
But again, I could be mistaking.
Hello,
I would like to ask a question regarding a show I recently saw on the history channel. If electrons look like particles while we observe them and act like wave while we don’t, is it possible that our observation is like the flash on a camera causing us to only see the electron in a single position, or the electron is truly not in a single place until it absorbs some of the energy from the light we use (to view it) to lock it in a single location.
Thanks,
Edwin Friskey
I cant remember what they do, but when I went scuba diving I was blowing bubbles, and they would rise to the surface…I’m trying to remember here if the big bubbles rose to the surface with the same speed as the small ones…easy to check…but what I think of here is of the few things I saw demonstrated in physics class, and that demonstration where a feather and a ball bearing fall at the same speed in a vacuum…now, the bubbles underwater are rising because they were made of air, and were in a denser medium, water…the pressure of the surrounding water forces them upward, in ‘bubbles’, to the lower pressure atmosphere above the ocean….I’ve tried to picture if stars and planets, all matter, aren’t ‘falling’, but rather ‘rising’ because of some density and pressure difference…that what we call empty space, is actually a denser something than matter…matter is to space what air is to water…well, maybe I’m thinking of the aether here?…I dunno…but the thought is that a black hole is just that, a hole in space, a kinda round little spherical bubble hole with the density of this aether around it, I imagine, and all matter, down to the tiniest, are lighter densiity than the aether, and are like tiny bubbles that will float/rise, not fall, into this black hole bubble, making a larger bubble we call a sun or planet…all things we know are bubbles, I might say!…and they join and separate according to the laws of physics, making the elements and compounds… this to say they are locked into their shapes (which are spheres at some point!) by the density of the surrounding aether…don’t electricians talk of ‘pressures’?…what would Tesla say of black holes, and the speed of light, and gravity?…explosives/explosions too are characterized as having pressure, yes?, and look very bubble like!…black holes are like an inside out explosions, matter exploding into them, even at the atomic size…we’re in the midst of a kind of exploding burning chaos…just day dreaming here…and making myself dizzy!…much to wonder about at this web site!
Can we use black holes to accelerate a space shutle to reach light speed?I mean if we stay close to the border of event horizon of a black hole that acts like a spinner or a vortex?
So many answers from people that have no earthly idea what you’re talking about. There’s no human on this forum are that exist on this planet that knows what goes on inside a black hole. Even the man in the wheelchair has no idea how to get out of the wheelchair but he knows everything about everything else. what we have here is just the human question. The search for an answer to something that we here in this time in this place won’t have an answer to. This little bubble that we live in won’t let us go that far. In other universes at different times these questions have been answered. And using infinity as a background they haven’t been answered. It pleases me knowing I’m on the edge of understanding this stupid thing called infinity. Understanding it yes explaining it to someone else no. I can say this when I reach that point I know there will be control of the world and universe around me. Sometimes the best answers are from the questions we don’t ask.as for the question asked, I’m sure that all the physics we’ve ever learned in our lives go completely out the window when you get to the center of a black hole. I’m pretty sure it doesn’t care whether we’re human or not. As far as matter disappearing and going away, where did the guy in the wheelchair get all his information from that’s what I want to know? That to me is more of an important question than knowing if gravity can actually overcome itself. Speculation is the worst thing that ever happened to the scientific world. since we have no base to go by, the majority of the questions I see on this site will never be answered here at this time in this universe. Sound crazy? Well who’s to say exactly what crazy is?
Oh, please.
We need to be objective on this. Criticizing scientists and certain theories will not do it. This theories have been proven true. Yes, there are scientist that go from science to pseudo-religion-sciences, but it doesn’t invalidate our knowledge of the universe. Yes, we know too little about it, but that too little does not equate nothing.
Now, for the topic of black holes. First, it is important to note that there is no known natural physical law that can explain what occurs beyond the event of horizon in a black hole. We know that a black hole is a singularity point in the spacetime curve whose surface is denominated as event of horizon, from which is theorized that nothing can escape. It is known that black holes emit electromagnetic radiation, which appears to escape from it, so it would seem like a contradiction. However, emission is different than escape. Light itself cannot escape from the gravitational pull caused by a black hole because the singularity point bends the spacetime curve as such that all time is essentially stopped. Escaping the bending of spacetime to move away from the event of horizon once trapped inside would require to travel faster than the speed of light, and thus far no information can escape. Black holes do rotate as they form from the rotation of particles to a common center, particles that once formed the star preceding the black hole, and it almost certainly has electromagnetic fields associated with it. Spacetime curve also has fields. In fact, vacuum itself has energy associated with it, and given that forced are mediated by particles travelling in spactime, fields are deduced to exist in the curve. As for whether it makes sense for gravitons to exist, gravitons would mediate the acceleration motion towards the presence of mass via the curvature of spacetime around that mass, in the same way other bosons mediate their other forces. However, we don’t have such a good understanding of gravity to know that it certainly works. hence completely discarding gravitons is irrational. We have no evidence to believe they exist, but we have no reason to believe they don’t. It’s just a matter of investigation and figuring it out.
IN the end, a quantum gravity theory is needed, regardless from how you look at it.
there is no moderation. it is simply a known fact among scientists and anyone else who cares to investigate. why do you people read something and because it is endorsed by SOME scientist assume it to be true without checking it out. that is what is not scientific.
I have worked on trying to understand the FTL region for years. The first thing you realize when you begin to understand its nature is that general relativity (as it is usually interpreted) is fundamentally wrong. For black holes particularly general relativity is pretty much directly incompatible with any sensible coherent model. Ultimately gravity still follows conservation of momentum which means that (kinetic) energy is crossing an FTL barrier at the outer event horizon. Even worse if there is a central singularity there must also be inner event horizons – to cross them the gravitational energy must be moving at close to the speed of FTL simultaneity- fast enough to cross the whole universe in a few seconds..
There are models where this problem does not occur – but they require a flat frame approach – in other words a non-curved space time…. You can have a flat frame and a curved space time but once you reach this point the standard model of general relativity is right out the window. In this new model physical space time is restricted to quantum scales and space time curvature becomes space time compression…
The curious bit is that with dimensional time limited to quantum scales the division between quantum mechanics and general relativity and classical mechanics disappears. The whole of physics is a quantum scale event – and unified to larger scales by the continuum of space. (I have developed a whole new model of physics from this – but it is still very much a work in progress..)
@Robert Lucien Howe:
The theory of general relativity is not fundamentally wrong; it’s fundamentally incomplete, in the exact same form as quantum mechanics theories are incomplete. Physicists are aware of this. Theory of relativity has been disputed since thery moment it was published and this had been an open question for over a century, really. Your approach does not solve the division between quantum mechanics and theory of relativity when it comes to scales. First, let me address that relativistic mechanics and classic mechanics are not divided unlike quantum mechanics and relativity are. Rather, relativity always supercedes classic mechanics, and it is actually understood that Newtonian physics are only a very specialized case of relativistic physics. As such, we know that both quantum physics and relativistic physics are both special cases of one bigger unknown physics theory, which is namely quantum gravity. Your approach does not solve that; it instead relies on ignoring general relativity, which simply creates many more problems and complications. If that was proper, then nothing we name science is true science, because no theory is complete. The theory of evolution is hardly developed and still incomplete, and so is the theory of Big Bang. That does not signifies they’re wrong and need to be thrown away, they simply mean that certain aspects and details need to be refined. Getting rid of our knowledge for being complete actually just equates getting rid of science as we know if we were to do the math. Ever since general relativity theory has been out there, black holes have represented a problem. That does not make it fundamentally wrong. Now, you can provide a new physics model, but it doesn’t solve the problem, it only modifies. It only gives us another specialized case of an unknown quantum gravity theory that has no completion either. The problem relies on the fact that individual particles behave in a particular way at the quantum level, but that the set of particles combined to higher magnitudes give emergent properties, radically changing their properties, giving rise to relativity. The problem is understanding how do these properties become emergent, at what point. That line hasn’t yet been drawn because there is yet no quantum gravity theory that holds up to full scrutiny.