What happens to time inside a black hole?

[Wazkick3n]

Since everything that has gravity warps space-time fabric in some way or another.
Would time stop or just slow down immensly inside a black hole or around the event horizon?

 

[twofish-quant]

Since everything that has gravity warps space-time fabric in some way or another.
Would time stop or just slow down immensly inside a black hole or around the event horizon?

It depends on what you mean by time slowing down. One thing that makes this question tricky is that when you start talking about changes in space and time, your rulers start changing and it can get a bit confusing to tell if something is changing when your rulers are also changing.

If I have a flashlight that pulses once per second and I aim it from the Earth to the moon, then the person on the moon will see it flashing at something slower than once per second. If I flash it from Jupiter then it will be even slower. From the sun, even slower. If I flash it from near a black hole, then the frequency of the flashes will slow down more and more until I cross the event horizon at which point I'm not going to see any further flashes.

Now if I look at the pulses, and it's a big enough black hole so that tidal forces don't matter, then I'm not going to see anything unusual.

So a lot depends on what you define as your "ruler". If your ruler is a clock that is on the moon then based on the clock, things will slow down. If your ruler is a clock that is falling into the black hole with you then things won't.

 

[kcajrenreb]

Do you mean time stopping as in no further change within thhe event horizon? If so, obviously not, there are warping and bending strings at its surface. But yes, time does slow down, tremendously.

 

[Chronos]

Time is difficult to define inside the event horizon. It is unfathomable to the external observer as time essentially halts at the event horizon. It implies time should move backwards inside the EH, but, that is illogical. We are fairly confident black holes exist and tend not to de-exist once formed so far as we can observe. I prefer to think of them as island universes in the sands of spacetime.

 

[ibysaiyan]

Can you elaborate us a little further as to what exactly you would like to know more about.Are you after an explanation of time inside the black hole or surrounding the event horizon.Time,is a dependent dimension i.e with respect to different reference frames,time would vary,not absolute which is illogical.

As for the radiating light surrounding the event horizon,to an external stationary observer light would appear to come as very red-shifted.I believe it was some poster on here who had mentioned that to an outward observer once the object gets into the EH,it doesn't go to a standstill ( as general relativity speaks) but it become more and more red-shifted to an extent that one photon is released in a said interval.

Someone correct me if I am mistaken.

Regards,
ibysaiyan

 

[Imax]

I prefer to think of them as island universes in the sands of spacetime.

Poetic

If light follows a straight line (i.e. a geodesic) and light can’t escape a black hole, then maybe there is no geodesic from inside the event horizon to outside. One way to express that mathematically is to look at closed manifolds.

 

[twofish-quant]

Time is difficult to define inside the event horizon.

Time is easy to define inside the event horizon relative to another observer within the event horizon. It's hard/maybe impossible to define relative to an observer outside the event horizon.

Think about this.

When you say that something happens at the same time, what do you mean?

Right now the time is X a.m. I get the time by looking at my cell phone, and then my cell phone talks the cell phone tower. The cell phone tower ultimately talks to the central UTC time keeping center. So to figure out what time it is, it involves sending messages back and forth.

Now if you are in a black hole, you can't send a message to someone on the outside, and so you can't define a way of agreeing what time it is.

It is unfathomable to the external observer as time essentially halts at the event horizon.

But it doesn't. If I cross an event horizon, I don't notice anything odd. My watch doesn't stop or anything like that. Now if I try to synch my watch to someone else's watch, I'll find out that I can't, but that's the definition of an event horizon.

It implies time should move backwards inside the EH, but, that is illogical.

For someone falling in, time appears to move normally. It's when you try to synchronize watches that you find out that something weird is happening.

 

[twofish-quant]

Part of the problem is define exactly what you mean by

"time slows down"

 

[Imax]

"time slows down"

Yes.

 

[Wazkick3n]

Part of the problem is define exactly what you mean by

"time slows down"

Well I mean, if you were inside a black hole or around the event horizon would time slow down for you? Similarly as time slows down as you approach the speed of light.

 

[Wazkick3n]

Or suppose what measure now as one second. If we keep that measurement constant and then go into a black hole's vicinity would that measurement of one second seem a lot longer?

 

[twofish-quant]

Well I mean, if you were inside a black hole or around the event horizon would time slow down for you? Similarly as time slows down as you approach the speed of light.

Actually it doesn't.

 

[twofish-quant]

Or suppose what measure now as one second. If we keep that measurement constant and then go into a black hole's vicinity would that measurement of one second seem a lot longer?

One second is defined as "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom". If you go near the black hole the gravity will have the same effect on your watch and the thing that you are using the watch to measure, so you notice nothing.

Now if move the watch near the black hole and then move the watch out again, then you'll notice that less time as passed on the watch that went near the black hole.

So the question is "slower relative to what?" That's why they call it relativity.

 

[Wazkick3n]

So does that mean that the watch will tick exactly as it would on Earth. If so, would time be perceived slower in a black hole than it is perceived on Earth? Or would it be perceived exactly the same?

 

[twofish-quant]

So does that mean that the watch will tick exactly as it would on Earth.

It's relative. :-) :-)

If you are next to the watch, it is going to look and act like a watch on earth.

If you bring the watch to the black hole and back to earth, you'll find that the watch that went to the black hole has had less time pass.

The tricky part is that you can only say that time is "slower" on the watch that went near the black hole and brought it back to Earth or if you sent some message from the black hole to Earth so that you can compare the numbers.

If you took the watch to the black hole and kept it there and you didn't send messages to synchronize the watches, then there is no way that you can compare the speed of the watches to see what is slower. If you cross the event horizon you can't get back and you can't send a message, so the question of which watch is slower, doesn't have any meaning.

 

[Wazkick3n]

I see now. But is there such thing as the physical feeling of time, possibly time dilation but I'm not sure, and if there is would that be slower RELATIVE to the time we feel now on Earth?

 

[mdmaaz]

Time would slow down near a black hole. Since all heavy objects have a gravitational field and that makes a dent in the fabric of space-time and causes time to run more slowly.

 

[cosmik debris]

This whole thing about "time slowing down" is the product of unclear thinking about what is going on. A clock co-located with an observer shows the proper time. A second is a second. If the clock and the observer are separated then the measurement (some sort of tangent vector) has to be parallel transported along a path on the manifold. The measurement value will change. It is all a matter of geometry, time doesn't change only the measurement of it changes.

 

[Nabeshin]

The measurement value will change. It is all a matter of geometry, time doesn't change only the measurement of it changes.

One could get into a long drawn-out discussion about what a thing is if not the measurement of that thing, but I think we'll avoid that here :)

 

[Chronos]

I assume most would agree measurements are only valid in the observer's reference frame.

 

[smartie18]

I can't imagine that time would stop anyhow. It would probably decrese or slow down. Or, it would stay the same but maybe our perception would change.

 

[ibysaiyan]

I see now. But is there such thing as the physical feeling of time, possibly time dilation but I'm not sure, and if there is would that be slower RELATIVE to the time we feel now on Earth?

You may have missed my post about the meaning of time.It's not something physical but in respect to object's change in position we eventally change our time coordinate as well.As quantfish mentioned ,reaching relativistic speed means ending up to a time paradox. For example ,there are two twin brothers of age thirty,one of them is sent into a space shuttle which reaches speed of light,the duration he's sent for is exactly one year to prior to his next birthday.His journey ends he returns back to Earth only to find out that his other twin is of 6 years older than him.The difference in the stretch factor is equal to the space contraction which the shuttle faces,I think.
Think of it as a function being stretched in the 'x' direction,basically that is what relativistic speed does.It stretches time in a sense.

Regards,
ibysaiyan

 

[ibysaiyan]

I can't imagine that time would stop anyhow. It would probably decrese or slow down. Or, it would stay the same but maybe our perception would change.

Theoretically it stops as the graph approaches to a stand still integer BUT relative to an observer at a distance further away from EH,the waves would appear to be going extremely large/red shifted until a point is reached where barely a photon appears in a time interval.

 

[Imax]

This whole thing about "time slowing down" is the product of unclear thinking about what is going on.

I agree. For an observer at an infinite distance from the black hole, or maybe some safe distance, time for anything falling into a black hole appears to slow down. The object would appear to decelerate, but it’s all relative. There would be no perceived time change for the object falling in.

 

[cosmik debris]

One could get into a long drawn-out discussion about what a thing is if not the measurement of that thing, but I think we'll avoid that here :)

That is not the issue. The issue is that the measurement changes depending on the position and motion of the observer. For the clock co-located with the observer falling into the hole nothing unusual happens. A second is a second.

 

[twofish-quant]

Also there is a cute solution to what happens within a black hole.

I look at my watch, it seems to act normally. My friend looks at their watch, it seems to act normally to him. Now how do you tell which watch is "slower." Well to do that, we send some sort of signal from one watch to another, or do something so that we can compare the values of the two watches.

But if one watch is in black hole, I *can't* compare the value of the two watches. So asking which watch is slower is impossible.

Random fact: You get into similar issues of rulers changing when dealing with things like currency markets. The value of a currency changes over time due to inflation, and trying to figure out how different "rulers" change over time gets you into the same sort of math that you use to model black holes.

http://papers.ssrn.com/sol3/papers.cfm?abstract_id=1458886

 

[cosmik debris]

Random fact: You get into similar issues of rulers changing when dealing with things like currency markets. The value of a currency changes over time due to inflation, and trying to figure out how different "rulers" change over time gets you into the same sort of math that you use to model black holes.

http://papers.ssrn.com/sol3/papers.cfm?abstract_id=1458886

Yes there's an interesting paper called I think "Economics in Curved Spacetime". It is essentially showing the fact that paths in curved spacetime are different lengths and moving currency via different paths can change the value of that currency just as the measurements of physical values of time and length change in relativity.

The different paths in the economic sense are converting US$ to Yen to English pounds, as opposed to US$ to AUS$ to English pounds.

 

[SamirS]

I see now. But is there such thing as the physical feeling of time, possibly time dilation but I'm not sure, and if there is would that be slower RELATIVE to the time we feel now on Earth?

If you will, time itself slows down relative to observers far away from a black hole. This means that any chemical process or whatever creates "the physical feeling of time" also slows down relative to observers far away from the black hole. YOU yourself, hypothetically standing next to a black hole, wouldn't feel any difference in the "flow of time". If you, however, stay there for some time and then return back to observers far away from the black hole, they will be noticably aged compared to you. If for them it was 20 years and for you 1 years, you felt 1 year pass and they felt 20 years pass.

You can't say any of these two is the "actual" time that passed. Said differently, staying near to a massive object like a black hole amounts to a form of "time travel" into the future of observers far away from the hole (note that this amounts to time travel for us because usually, all humans experience about the same time due to low velocity and low gravity). However, you still can't zoom out to some metaphysical level and arbitrarily define it as "The Time".

If you want to understand this and resolve the apparent paradox, you have to get away from the (intuitive) idea that our usual reference frame on the Earth is the frame against which all others are benchmarked.

 

[cosmik debris]

If you will, time itself slows down relative to observers far away from a black hole. This means that any chemical process or whatever creates "the physical feeling of time" also slows down relative to observers far away from the black hole. YOU yourself, hypothetically standing next to a black hole, wouldn't feel any difference in the "flow of time". If you, however, stay there for some time and then return back to observers far away from the black hole, they will be noticably aged compared to you. If for them it was 20 years and for you 1 years, you felt 1 year pass and they felt 20 years pass.

You can't say any of these two is the "actual" time that passed. Said differently, staying near to a massive object like a black hole amounts to a form of "time travel" into the future of observers far away from the hole (note that this amounts to time travel for us because usually, all humans experience about the same time due to low velocity and low gravity). However, you still can't zoom out to some metaphysical level and arbitrarily define it as "The Time".

If you want to understand this and resolve the apparent paradox, you have to get away from the (intuitive) idea that our usual reference frame on the Earth is the frame against which all others are benchmarked.

Yes, this is the gravitational form of the SR "twin paradox".

 

[Wazkick3n]

So as I can understand here, the actual "feeling of time" doesn't change if you were near a black hole or in it. It however does slow down the properties of time does it not, as is suggested by the twin paradox?