Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[XXXXYYYY]

PTW

[Tylui]

First off, I wanna apologize to Il Palazzo for our discussion several pages back. I'm still iffy on the spring example, although I'm not necessarily doubting its veracity, just I don't understand it.

Secondly, I want to apologize for bringing something up from a couple of pages back.

Time dilation seems to be asymptotic at the event horizon - that is, it is infinite according to relativity theory. This has some interesting implications, for example you see everything further away from the black hole speed up immensely, which includes everything else that is destined to hit the black hole. Take that to the logical extreme and it means everything that fell in before you or after you hits the event horizon at the same subjective moment that you do.

That's the problem with those models that say you fall through the event horizon without noticing anything in particular, they fail to account for all the other matter that's doing the same thing you are.

As you're falling into the event horizon, YOU are not experiencing time dilation. Your watch ticks off a second every second, like normal. It's the people who are watching from outside the black hole who see your watch tick slower. To them, you never pass through the horizon at all. To you, you pass through it without anything special happening; you truly wouldn't even notice it. Another way to put it is that the objects falling in behind you aren't accelerating faster than what you are.

[Sergarr]

Time dilation seems to be asymptotic at the event horizon - that is, it is infinite according to relativity theory. This has some interesting implications, for example you see everything further away from the black hole speed up immensely, which includes everything else that is destined to hit the black hole. Take that to the logical extreme and it means everything that fell in before you or after you hits the event horizon at the same subjective moment that you do.

That's the problem with those models that say you fall through the event horizon without noticing anything in particular, they fail to account for all the other matter that's doing the same thing you are.

As you're falling into the event horizon, YOU are not experiencing time dilation. Your watch ticks off a second every second, like normal. It's the people who are watching from outside the black hole who see your watch tick slower. To them, you never pass through the horizon at all. To you, you pass through it without anything special happening; you truly wouldn't even notice it. Another way to put it is that the objects falling in behind you aren't accelerating faster than what you are.

Sure, but you know what the fun thing is? You also cannot accelerate faster than the object before you, and you will never observe it falling into the black hole by definition, so you, by the virtue of being behind it, will also never fall into the black hole.

I'm also sure there's some problem with my argument that makes it invalid, but it's a pretty fun one.

[wierd]

Red dwarf systems also tend to be "Metal poor."  To astronomers, "Metal" is anything heavier than helium.  Not many heavy elements are typically expected in red dwarf systems, which means that large quantities of crust oxygen is not anticipated like you would expect in a more metal rich system.

[i2amroy]

Thing is it's entirely possible for a planet to lose then regain its atmosphere. IIRC the Earth did that at one point (it started off with a hydrogen/helium atmosphere, which was then blown away to be replaced by gasses from outgassing.)

Yeah, Earth and any others of the inner planets with atmospheres are all secondary atmospheres. Jupiter, Saturn, and the other jovian planets are all still on their primary ones.

Another interesting fact, pretty much all the oxygen currently in the atmosphere is life-produced oxygen. Should all life be suddenly extinguished on Earth, we would lose any remaining oxygen on a timescale measured in thousands of years. (Which is why one of the big things astronomers search for on other planets is oxygen in the atmosphere, since it's a very good indicator that there would be life on the planet).

[Il Palazzo]

Red dwarf systems also tend to be "Metal poor."  To astronomers, "Metal" is anything heavier than helium.  Not many heavy elements are typically expected in red dwarf systems, which means that large quantities of crust oxygen is not anticipated like you would expect in a more metal rich system.

That's only by the virtue of their longevity. You make it sound like it's an inherent property of being a red dwarf, whereas it's just statistics.

Regarding the source for the earlier statement, have you got something more rigorous than a one-sentence mention in a textbook? I've been hearing bits and pieces about this phase every now and then (it's called the T-Tauri event), but never could get my hands on anything more in-depth.

(The book seems nice, though. I've just bought a used copy for two bucks on Amazon. )

Sure, but you know what the fun thing is? You also cannot accelerate faster than the object before you, and you will never observe it falling into the black hole by definition, so you, by the virtue of being behind it, will also never fall into the black hole.

I'm also sure there's some problem with my argument that makes it invalid, but it's a pretty fun one.

Not feeling too comfortable in the subject, I can only tell you what I heard about it.
The problem is that you can't use the same frame of reference for the in-falling observer as you do for a stationary one. The solution where the in-falling object never crosses the horizon is only valid in the reference frame of a static observer outside the event horizon. For the in-falling observer you need to use a different set of coordinates:
http://en.wikipedia.org/wiki/Gullstrand%E2%80%93Painlev%C3%A9_coordinates


@Tylui: I don't think there's anything to apologise for, but cheers.

[scrdest]

Red dwarf systems also tend to be "Metal poor."  To astronomers, "Metal" is anything heavier than helium.  Not many heavy elements are typically expected in red dwarf systems, which means that large quantities of crust oxygen is not anticipated like you would expect in a more metal rich system.

So, for an astronomer oxygen is a metal? I find that somewhat amusing.

[That Wolf]

It seems time cant be discribed properly.
Would that mean it doesnt exsist? Anything that exsists we seem to be able to measure it, atleast when we can grasp at it
For example: 'Now', is only perspective. Its not actualy a static meaning. I can touch my foot with my hand and feel both sensations 'now' but its not at the same time. One is delayed because one sensation had to travel a longer distance.
So is time like much of what we perceive just an evolved system to deal with the chaotic universe we reside in? Perhaps space is the same hence why it looks 3 dimensional? From your position outwards? To combat the reciving of information (impossible to take it all in at your position so the information is only what is 'near' you)
Did I make sense?
The space idea was just thought up. Im more interested in what people have to say about time.

[Il Palazzo]

Time is what clocks measure.

[Sergarr]

Not feeling too comfortable in the subject, I can only tell you what I heard about it.
The problem is that you can't use the same frame of reference for the in-falling observer as you do for a stationary one. The solution where the in-falling object never crosses the horizon is only valid in the reference frame of a static observer outside the event horizon. For the in-falling observer you need to use a different set of coordinates:
http://en.wikipedia.org/wiki/Gullstrand%E2%80%93Painlev%C3%A9_coordinates

That's a very interesting link!

However, I'm not sure how my argument relies on any specific qualities of a stationary frame of reference. By its nature the black hole should be unobservable from all frames of reference outside of it, and thus anything falling into it will never get observed. Given that no matter how one compresses space, you will never end up in the front of something that was in the front of you, you get this funny paradox of "you can't fall into black hole until you observe the thing in front of you falling in, which cannot happen" which is obviously wrong as you can fall into black holes.

It's kinda similar to Zeno's paradoxes in that sense.

[Il Palazzo]

In your argument you said

you will never observe (an object) falling into the black hole by definition

which is not true in the in-falling coordinates.

[Frumple]

Pretty sure trials in monkeys (or maybe apes) with head transplants have been semi successful, in as much as the subject lived for a number of hours before expiry. Not fab, but its a start.

My memory's definitely spotty, but weren't the test subjects put down instead of dying naturally/due to complications/whatever?

[Sergarr]

In your argument you said

you will never observe (an object) falling into the black hole by definition

which is not true in the in-falling coordinates.

Hmmm.

What if we give the falling observer and the object-before-it a propulsion system that would exactly counteract the gravity acceleration at any moment of falling down? That would make them stationary.

[Il Palazzo]

What if we give the falling observer and the object-before-it a propulsion system that would exactly counteract the gravity acceleration at any moment of falling down? That would make them stationary.

If they're stationary, then they're not in-falling, no?

[Sergarr]

What if we give the falling observer and the object-before-it a propulsion system that would exactly counteract the gravity acceleration at any moment of falling down? That would make them stationary.

If they're stationary, then they're not in-falling, no?

They can still move at a constant speed relative to the black hole and be considered a "stationary observer".