Stephen Hawking's new way of perceiving black holes !

Post by **weixing** » Tue Jul 20, 2004 1:32 pm

Hi,
The following are from some website that explain your question:

The light is "redshifted" to longer wavelengths as it rises away from the black hole. So if the object are emitting visible light at some particular wavelength, the observer will see light at some longer wavelength. The wavelengths get longer and longer as the object get closer and closer to the horizon. Eventually, it won't be visible light at all: it will be infrared radiation, then radio waves. At some point the wavelengths will be so long that the observer will be unable to observe them. Furthermore, remember that light is emitted in individual packets called photons. Suppose the object are emitting photons as the object fall past the horizon. At some point, the object will emit it last photon before the object cross the horizon. That photon will reach the observer at some finite time -- typically less than an hour for that million-solar-mass black hole -- and after that the observer will never be able to see the object again. (After all, none of the photons the object emit *after* the object cross the horizon will ever get to the observer.)

As what above explain, the object will turn red and fade away.

Have a nice day.

Post by Q » Tue Jul 20, 2004 5:07 pm

wow, thanks, that never cross my mind before... lol

Post by **zong** » Tue Jul 20, 2004 8:42 pm

Wow thanks weixing.. you explained what I had tried to explain for so long.. Maybe I really should start brushing up my english skills so that I can explain properly..

ChaosKnight wrote:Alright, riddle me this: within strong gravitational fields, time slows down. Will time come to a standstill if the gravitational field is strong enough to trap light?

More fun questions! I like'em.

This question hinges on the idea of time dilation. It is possible for time to come to a standstill in mathematical terms. This will be when the space-time dimension has been stretched to infinity. This can only (theoretically) happen when very very very near to the black hole itself. A G-field just strong enough to trap light still cannot bring time to a standstill, only slow it down very drastically.

Kamikazer · Post by **Kamikazer** » Tue Jul 20, 2004 10:41 pm

anyone can explain the time-space thingy?
or know of any references i can read up on to understand that topic further?

QuantumGravity · Post by **QuantumGravity** » Tue Jul 20, 2004 11:05 pm

Stephen Hawking books (Brief history and nutshell) are probably still one of the best out there.

ChaosKnight · Post by **ChaosKnight** » Wed Jul 21, 2004 11:55 am

Alright, there is no paradox then.

Another question, zong.

Suppose there were two observers, A and B.
A is stationary.
B is accelerating at constant magnitude as observed by A.
B will see A accelerating in the opposite direction, but will the magnitude be a constant also??

i am thinking acclerations observed by both are different, but if one is constant, the other is.

Post by **weixing** » Wed Jul 21, 2004 12:20 pm

Hi,

Suppose there were two observers, A and B.
A is stationary.
B is accelerating at constant magnitude as observed by A.
B will see A accelerating in the opposite direction, but will the magnitude be a constant also??

i am thinking acclerations observed by both are different, but if one is constant, the other is.

Both will observe the same acceleration.

Anyway, please post any new question on a new topic... OK

Or else, this thread will become "The Never Ending Story"..

Have a nice day.

ChaosKnight · Post by **ChaosKnight** » Wed Jul 21, 2004 12:52 pm

No, observation of same accleration is impossible (if my math is correct). My question is whether both observers see constant acceleration.

This question has something related to black holes, if i can find the correct link between these issues. Somehow.

Post by **weixing** » Wed Jul 21, 2004 1:20 pm

Hi,
I really don't understand what you mean??? May be you want to explain why both observer cannot observe the same acceleration... since only B is accelerating and A is stationary... my math is not that good lah...

??

Have a nice day.

ChaosKnight · Post by **ChaosKnight** » Wed Jul 21, 2004 2:20 pm

Sorry i take that back. Different observers can see the same acceleration if at that point in time their velocity is the same. But this is generally not the case.

Since both observers agree on their relative velocity, but since they cannot agree on time, they also cannot agree on acceleration. Can somebody confirm this??