# Thread: Black holes and the speed of light

I don't argue. I just regurgitate the same information over again.

2. Holla! I'm a senior physics major at pennstate! Minor in math, though that hardly matters =p,
but to answer the SECOND part of your question, as everyone has already stated that the speed of light is constant, when light is affected by a force like gravity, it will either red-shift, or blue-shift. Basically the speed is constant but it will change it's energy. This is actually why sunsets and rises are red... kinda... when the light bumps through our atmosphere it looses energy. When it looses energy it changes color to be more red. If light were to be directed out of a high gravity environment it looses energy.
You actually knew red was a low energy color as well. Red lights wont damage night vision, and everyone worries about ultra violate radiation hurting your skin, infrared, not so much.
Sorry if my grammar is poor, donating blood and typing with one hand.

3. I'm not a physicist but it's a rather simple question.
The light bends. As for the speed, light can't lose speed, but it loses energy via redshift.
http://en.wikipedia.org/wiki/Gravitational_redshift

Refraction is a change in direction, and not a change in magnitude.
Which results in the effective speed of light in water being slower than when in a vacuum. It's a point everyone understands, don't start a meaningless argument over semantics.

However as Rukentuts mentioned, we are talking about it in a vacuum and thus refraction is irrelevant.
And I said it's a constant in a vacuum, so what exactly is your problem again?

5. Originally Posted by algoferon
Light has speed, not velocity. If velocity of the light was constant and unaffected by optical mediums then we would not have rainbows or shiny, precious diamonds /sigh
also if light only had speed but no velocity then it would't GO anywhere. It travels in a direction, thus it has a velocity. We have pretty color shifts because light itself... white light mind you.... has every color and wavelength in it.... different wavelengths diffract at different angles producing a rainbow.

6. Originally Posted by Rukentuts
The speed in a vacuum is constant.
I just said that it is. Like, with almost the same exact words.

7. It's actually a pretty big deal in terms of physics that can happen in said medium.

If i have light that i somehow capture between 2 mirrors, that doesn't mean the speed went to 0, it's just redirected. Not sure if you've ever had to do work on the topic, but the difference is noble prize worthy if you prove it slows down. Not semantics

8. Originally Posted by Demoness
Hello all,

I am not educated in the mathematics and computations required to calculate orbits and material phases, but I have a very good ability to grasp and understand the concepts of astro physics explained. My favorite scientists to hear speak are Neil Tyson, William Nye, and Stephen Hawking(not really speak, but maybe read). When I see these men speaking before audiences, and allow questions at the end of their presentations, they allow the audience to ask several questions. The audience nearly always ask rhetorical or philosophical questions rather than detailed technical questions, which of course I am most interested in. I have a few questions that I believe can be answered, but I have yet to hear asked:

If light behaves as both a particle, and a wave, and light can be affected by gravity, such as being unable to escape an event horizon of a black hole, then what happens when light passes near a black hole, but stays outside the event horizon? Does light possibly enter orbit, or simply change direction and speed? If light changes speed, does it speed up going towards the black hole, and slow down leaving the black hole? If light changes velocity based on gravity, then how can the speed of light be a constant? Is the constant of the speed of light simply a maximum attainable speed, leaving light able to slow down to an extent before becoming a form of matter?

I would like to hear anyone's thoughts on this subject, or even better, I would like to see links to sources that can answer my questions. These can either be reading material, or videos. In the off chance that any of you regulars of MMO-Champion are astrophysicists or theoretical physicists, would you please shed some light on my questions?
Light will bend around any massive object such as a black hole. This effect warps the appearance of things behind it. The effect is called gravitational lensing. Here's an artist's conception.

The Schwarzchild Radius is the point at which light can no longer escape. Light precisely at the Schwarzchild Radius is in orbit around the singularity.

---------- Post added 2012-10-03 at 06:44 PM ----------

Originally Posted by semaphore
Sure there is. Light slows down when it passes into, say, water. That's a change.
That's not because the speed actually changes. Light just bounces off the atoms in the medium. It's still traveling at 2.99*108 m/s between the atoms, though.

9. Around a black hole (and actually neutron stars as well) there is a certain distance away from the event horizon or surface of the star that is called the photon sphere. In this very thin area photons actually orbit a black hole/neutron star. Other than that area it either flies off into space or plummets into the object. Another thing for light falling into a black hole, as long as the light is emitted outside the event horizon it will be traveling at it's maximum speed, although it may appear redder due to energy loss depending how close to the black hole it was emitted from. Inside a black hole, it either goes straight to the center when emitted, or around the singularity as it goes in, kinda like when you flush a toilet, but the speed itself never changes.

10. Yes, if close enough, light orbits the black hole. That means, that if u could stand besides a black hole, u would see your own neck.

And if im not mistaken, this is how we spot black holes aswell. we cant see the black holes themselves, but we see a black spot that distorts the light around it.

11. Originally Posted by Damonharp
also if light only had speed but no velocity then it would't GO anywhere. It travels in a direction, thus it has a velocity. We have pretty color shifts because light itself... white light mind you.... has every color and wavelength in it.... different wavelengths diffract at different angles producing a rainbow.
Probably I confuse the speed of light ( $u=\lambda\cdot f$ ) with the velocity of propagation of the light, who knows... Diffraction would not be possible if the velocity was constant, is what I wrote. Perhaps my syntax is wrong or something.

12. Originally Posted by Laize
That's not because the speed actually changes. Light just bounces off the atoms in the medium. It's still traveling at 2.99*108 m/s between the atoms, though.
Which means that the speed at which light propagate through the medium changes. It's not like I coined a new expression here.

13. Originally Posted by algoferon
Probably I confuse the speed of light ( $u=\lambda\cdot f$ ) with the velocity of propagation of the light, who knows... Diffraction would not be possible if the velocity was constant, is what I wrote. Perhaps my syntax is wrong or something.
The velocity is constant because the wavelength is directly proportional to the frequency of the wave. Long wave lengths have lower frequency. Also the symbol "lambda" is the symbol for wavelength and c is the symbol for the velocity when dealing with light cus constant

Also the speed of the light particles never changes, the only reason it moves slower through glass and water and such is because it bumps into so many other particles, the speed it travels between the particles it bounces in is still the speed of light. As soon as it gets out of the water or whatever it goes through, it regains its normal speed without affection from an outside force. a particle with mass would not be able to do that.

14. If you really want to understand this, you'll need to take a few classes. Photons cannot be directly affected by gravity as they have no mass. They must follow the curve of space-time as they travel always searching for the shortest distance between two points. Massive objects bend space-time and create basically wells in the 'fabric' which these photons will proceed to enter and exit traveling on the curved space.

As far as wavelength goes, for photons, you must use the de-brogile wavelength formula (i probably spelled that incorrectly). (Lambda=(planck const)/(relativistic momentum)

Also, the photon's energy shifts as it bends around objects as it gain an angular acceleration, ect...

Anyways...

Photons may never be treated classically.

15. Reading this thread is making me feel inadequate =/

16. any speeds traveld is based upon preception.

let's say you are sitting in a chair and live on a nice tropical island in the equator. Right then and there you are gonig roughly 1,000 miles per hour due to the earth's spin. everything arround you is also going that fast but to you it's all standing still. a car passing heading east is going that + it's speed. going west - it's speed.

now let's take it a bit further.

the earth rotates arround the sun at 66,500 mph. add anohter 1,000 from rotation at points where your placement upon the earth lines up with the earth orbit arround the sun and obiously - that when opposite side during it's orbit.

OMG EVERYONE IS BREAKING THE SPEED LIMIT !!!

wait that's not all!!!

If the big bang theory is true however fast the mass was ejected is how fast the stars/solar systems ect is traveling away from 1 fixed point. We may allready be going at the speed of light (or close to it).

if object a is traveling at the speed of light east and object b is traveling in the oposite direction at the speed of light. If object A can be preceived to be standing still object b will be going 2x the speed of light from the point of preception of object a.

We consider objects when they impact each other to head on we considere both speeds combined to give us an impact speed. so techincally yes you could have an impact of 2x the speed of light if 2 objects going the speed of light hit each other head on.

17. Originally Posted by Dacien
Meh, they may know a lot about physics, but I'm sure there are a couple things between us that we know a lot about and they know next to nothing about. lol, it's just a matter of finding it.

Refraction is a change in direction, and not a change in magnitude.
It is both, refraction index is some simple function of light speed in the medium, and you can calculate the refraction angel from the principle that the light path is the fastest path.

19. black holes are super tiny, except for a select few in the center of galaxies, and we can't even "see" those through the method you described. We know they are there due to the gravitational effects it has on surrounding stars. As for stellar mass black holes they are discovered through x-ray signals coming from the accretion disks around them as matter is falling in. These accretion disks super heat and let off a lot of heat and x-rays before the matter is consumed, this ultra-high intensity signals is what points us to black holes.

The other method, although not as easy to confirm, is when a relatively large star orbits an unseen companion, using estimations on distance, size, and mass of the star, it could be extrapolated to see how massive the companion object is, depending on how massive it is, it could either be an unseen neutron star -the light from the big star could be drowning it out- or a black hole.

20. Originally Posted by Laize
Light will bend around any massive object such as a black hole. This effect warps the appearance of things behind it. The effect is called gravitational lensing. Here's an artist's conception.

The Schwarzchild Radius is the point at which light can no longer escape. Light precisely at the Schwarzchild Radius is in orbit around the singularity.

---------- Post added 2012-10-03 at 06:44 PM ----------

That's not because the speed actually changes. Light just bounces off the atoms in the medium. It's still traveling at 2.99*108 m/s between the atoms, though.
While I appreciate everyone's contribution to the discussion, I was not wanting lessons in elementary physics terminology. This poster pretty much hit the nail on the head as far as what I was wanting to discuss. Thank you sir/madam.

I am glad I was somewhat correct in assuming that light is capable of orbit. So the Schwarzchild radius is similar to the event horizon? I was under the impression that the event horizon was the point at which light could no longer escape, since that is the point at which no communication or passage was possible. My question is how do these differ from one another?

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