Time dilation vs contraction:

Commotion Ocean

As we all know, the more you approach the speed of light, time begins to dilate and space begins to contract. This is referred to as time dilation, ie, more time passes for the observers than for the traveler.

Another scenario, is the astronaut in space. For every 100000 seconds passing for the astronaut, 100001 seconds will pass on Earth. More time is passing for the observers than for the traveler, so, logically, this too is time dilation.

In the scenario above, time dilation occurs AWAY from Earth where the traveler is less affected by Earth's gravity.

So logically, time dilation occurs where the traveler is "less affected by gravity".

According to a text I read, "gravity dilates time and time is completely dilated in a black hole" (which I believe is untrue). Logically, would time not be CONTRACTED in a black hole?

If 1 year in space is 1 year+1 second on Earth.
Logically, 1 year in a black hole should = 1 day in empty space.


See attached picture with my reasoning.

Morbert

Gravitational time dilation will make a clock on earth run more slowly than a clock away from earth. Your orbiting astronaut would experience 1 week + 1 second, while we on earth would experience one week.

Similarly, if you started surfing near a black hole, you would see the universe above you speed up, while people watching you from space would see you slow down.

Commotion Ocean

Morbert wrote: »

Gravitational time dilation will make a clock on earth run more slowly than a clock away from earth. Your orbiting astronaut would experience 1 week + 1 second, while we on earth would experience one week.

Similarly, if you started surfing near a black hole, you would see the universe above you speed up, while people watching you from space would see you slow down.

Ah ok, so "more time passes" (to put it very simply) for the person experiencing "less gravity". Theoretically, then, our good friends in Nepal are travelling through time quicker than we are :P

Fourier

Commotion Ocean wrote: »

Ah ok, so "more time passes" (to put it very simply) for the person experiencing "less gravity". Theoretically, then, our good friends in Nepal are travelling through time quicker than we are :P

Not theoretical at all. In fact time dilation has been measured at as little as one meter off the ground.

Raycyst

If you fall into the black hole at the event horizon the outside world would speed up, and you'd see the end of time.

But surely you'd also be hit by everything that falls into the black hole, including radiation which would burn you up, and physical stuff too. So you'd die at the event horizon.



Is that right?
Imagine falling into the black hole.
As you look out you'd see the universe get brighter, because more radiation is falling in for each of your subjective seconds, as your time has slowed down.
As you get closer to the event horizon the universe outside would get brighter and brighter, until just at the event horizon you'd be burnt up in a flash of radiation from outside.

Raycyst

Morbert wrote: »

...
Similarly, if you started surfing near a black hole, you would see the universe above you speed up, while people watching you from space would see you slow down.

If people looking in see you slow down then you must also get fainter.

If you had been emitting light at the rate of one photon per second and you now slow down you will be emitting less light and so you'll be fainter.

If you were emitting clock ticks at one tick per second you obviously emit less of them when you are perceived from outside as having slowed down.


The reverse must also be true.
You would hear clock ticks coming from outside the black hole speed up until they came so fast you couldn't distuingish them.
Photons from outside will also increase in intensity until you're fried.




edit to add: The fact that light is quantitised means that there is a limit to your faintness. At some point you dissappear like the chesire cat.

Raycyst

Well, I've been thinking a lot more about this.

I'm no expert by the way.

I was wondering if its correct say that a person falling into a black hole will appear to get fainter as he approachs the event horizon. Perhaps he'll remain visible at a similar intensity but he'll change colour instead.
Parhaps changing colour and reducing in intensity are the same thing?


As a result of my thoughts I've now changed my opinion as to what you'll see happening outside if you fall into a black hole.
Previously I said that the universe would get brighter until you were fried.
Now I realise that really what's happening is the frequency of the light waves coming from outside increase, but this changes their colour, and so really what happens is, the universe outside changes colour.
The colours are shifted towards the more energetic end of the spectrum, i.e towards blue light and towards x-rays. This means visible light is shifted until you can no longer see it, and radio waves and microwaves are shifted into the visible light spectrum.
When viewed in radio waves the universe likely looks very different. That's what you'd see. Eventually the cosmic microwave background itself would become visible.
That means the cosmic microwave background, which had been released during the Big Bang as gamma rays, and which had become massively stretched over the lifetime of the universe into microwaves, would now be shifted or compressed again into visible light!, and perhaps beyond that again into gamma rays!



I previously said that the universe gets brighter and brighter until you're fried. That is also true but what is happening is that what had previously been visible light would get shifted (blue shifted I think), and it'd become x-rays first, and then gamma rays. So you are fried, but not by visible light, but by what the visible light had become, hugely energetic gamma rays.