Black holes and the Speed of light

[Ursa Major]

Hello,

We have evidence that suggests that black holes bend light and pull it in by watching black holes cross in front of stars.

Now, does this gravitational effect from black holes not only bend the light, but also change its speed?

Will light speed up as it approaches a black hole and then slow down as it goes past and moves away from the black hole?

Or is the speed of light completely fixed and cannot slow down or speed up tiny amounts due to gravity?

I think that at the end of the universe, all the matter will by pulled in due to gravity to one point and cause another big bang (like how stars form from clouds of gas). If light does stay at a fixed speed, then will it be lost to whatever is out beyond the universe, or will it somehow be kept in orbit around the supper super super massive black hole at the end of the universe and gradually be pulled in?

These are just my ideas and there are probably many flaws in them but hopefully I have given you something to think about and would love to hear what you think of it.

Thank you.

[Phil Fargaze]

You got me thinking now!

I cannot comment on the effects of the speed of light, but many years ago I used to think that galaxies were little plug holes in space. Nowadays it is said that there are black holes in the centre of many galaxies. I sometimes think that, in the future, the universe will be populated by many black holes which will coalesce to form one final black hole which would destroy our universe to create a new universe. Our universe would have existed for many years, but for an observer on `the other side` the destruction of our universe to create another universe would happen in an instant, i.e. another `Big Bang`

[Ursa Major]

I wonder, if this theory is correct and this process has been going on for an infinite amount of time, then there will be infinite amounts of humans, meaning infinite amounts of me and you. Now that’s creepy.

[ronin]

Black holes bend space/time, not light.

Light travels through this space time so follows the bend of it.

A car on a banked race track does the same.

A black hole drags space/time into it, when the rate at which space/time being dragged in exceeds the speed of light then the medium that light travels in is being dragged "down" faster then the light can travel up so it never escapes.

Salmon in a waterfall is an analogy, if the salmon swims up at 5 kpm but the water flows down at 10 kpm then the salmon is swimming up in a medium that is flowing down faster then it is. So it goes backwards. Boats and tides are similar.

[Karlos]

Generally all laws of physics have conservation of all things, which is why I agree with you Phil, I believe that it is likely to be a cycle. I once heard a similar analogy to Ronin. A man is in a spacecraft near a black hole his partner jumps out, as she approaches the event horizon to him she appears be slowing down and coming to a complete stop, where as what she sees is him disappearing very quickly until disappearing forever, after she has passed the event horizon (That mean line you don't want to cross ) What interests me most, is what dark matter is, the kind of mass needed to hold together these galaxies is not present in these black holes at the centre of them, so there must be something else in the mix holding things together not to mention the outside and inside of these galaxies are travelling at the same speed, everytime I think of that the more I love how weird space is

[chemtom24]

as has been said a blackhole bends spacetime, so the light as far as it is concerned is travelling in a straight line, its the medium its travelling through which is curved ( think of a spheres surface - you can walk in a straight line but go around a curve)

however i have read somewhere that objects with mass are accelerated as they pass near black holes - i think i was reading about asteroids and how they can change their course. but anyway, yes, a blackhole will pull on an object that gets near and flick it out again. ( think of rolling a ball down a piece of guttering, then as it reaches the bottom, you swing the guttering to flick the ball out )

[JulianO]

What interests me most, is what dark matter is, the kind of mass needed to hold together these galaxies is not present in these black holes at the centre of them, so there must be something else in the mix holding things together not to mention the outside and inside of these galaxies are travelling at the same speed, everytime I think of that the more I love how weird space is

I think the current thinking is that black holes swallow up matter, both normal and dark, as they are both gravitationally attracted.

[George Jones]

Just a bit of an expansion on what JulianO wrote.

Dark matter does fall into black holes. As normal matter falls towards a black hole (electromagnetic) frictional forces heat up the matter, which then radiates away energy. This helps normal matter spiral into a black hole. Dark matter does not interact through electromagnetism and doesn't experience these frictional forces. Dark matter does fall into black holes, but, because of the lack of friction, a black hole presents a smaller effective target for dark matter than it does for normal matter.

[Zakalwe]

You got me thinking now!

I cannot comment on the effects of the speed of light, but many years ago I used to think that galaxies were little plug holes in space. Nowadays it is said that there are black holes in the centre of many galaxies. I sometimes think that, in the future, the universe will be populated by many black holes which will coalesce to form one final black hole which would destroy our universe to create a new universe. Our universe would have existed for many years, but for an observer on `the other side` the destruction of our universe to create another universe would happen in an instant, i.e. another `Big Bang`

Matter in a black hole exerts the same gravitational pull as matter outside a black hole. For example, if the Sun was replaced instantaneously by a black hole of the same mass, then the orbits of the planets would remain as-is (it'd get awfully cold and dark though!).

Current thinking suggests that there is not enough matter in the universe to slow the expansion to a point where it starts to contract (hence dark matter and dark energy), so it matters not a jot if that matter is in a black hole or not.

[Ad Astra]

Nothing is capable of changing the speed of light - it is the same for all observers in every reference frame - no matter how they are moving or how the source of light is moving. The Doppler effect for light changes frequency, not speed.

Michelson and Morley proved this with the interference experiment (which proved the Aether did not exist), but it took Einstein to correctly interpret their stunning results.

This conservation of the speed of light is the fundamental principle upon which Einstein's theory of relativity is based.

Dan

[damnut]

There have been some results in finding that a black hole has acted like a gravitational lens.

Some images from Hubble showed two identical galaxies in the vertical plane on overlay these were the same object. Something in the middle was producing the two images. It was summised that this could only be a black hole.

[JulianO]

There have been some results in finding that a black hole has acted like a gravitational lens.

Well its hardly surprising. Gravitational lensing happens when a large mass distorts space causing light (and anything else trying to follow a straight line) to bend. So black holes are ideal gravitational lenses in some respects. They bend space from a very concentrated point mass.

Some images from Hubble showed two identical galaxies in the vertical plane on overlay these were the same object. Something in the middle was producing the two images. It was summised that this could only be a black hole.

Certainly possible, but generally you can see black holes, or at least their effects. They are either at the center of galaxies (super massive variants) so clearly surrounded by other stuff, or have material flowing into them (dust, gas etc) which gives of radiation. Black holes that are invisible (i.e. completely black) are probably the exception - they'd have to be somewhere where there is no material to fall into them.