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I'm far too dumb to select an appropriate category: Thought for the Day

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  1.  
    Oh, I dunno about puny. A few H-bombs would sure change that scenery
  2.  
    Posted By: alsetalokinBeauty. The awesomness of nature, the punyness of humanity.

    Who but us could appreciate it?
  3.  
    Consciousness
    Dark energy
    Dark matter
    Entanglement
    Dimensionality

    The more you know, the more you know how little you know
    •  
      CommentAuthormagic moment
    • CommentTimeNov 11th 2014 edited
     
    I've known that all my life.
  5.  
    There's something fundamentally cacked about thinking that time is just another dimension. It's not like we can travel forwards and backwards in it and return to where we started, like in any other respectable spatial dimension. It's a dimensional imposter!
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      CommentAuthorpcstru
    • CommentTimeNov 19th 2014
     
    Posted By: Andrew PalfreymanThere's something fundamentally cacked about thinking that time is just another dimension. It's not like we can travel forwards and backwards in it and return to where we started, like in any other respectable spatial dimension. It's a dimensional imposter!

    The 'flow' of time is like travel in 3 space beyond an (gravitational) event horizon, you can only move towards the singularity. In the case of time, the singularity is (the thing of) the big bang and direction of travel is 'away' from the singularity.

    Or that might just be woo.
  7.  
    It's completely accurate. Although physicists like to use Rindler coordinates in such situations..I don't bloody understand them anyway, and in any case what you say remains true for any coordinate system, damnable or not. In a sense time and space reverse roles inside the event horizon. So this is all very strange.

    What if, say, we construct a collapse into a black hole nested inside another one. Then when we cross the second, inner event horizon, does time go back to being boring and space likewise?
    • CommentAuthortinker
    • CommentTimeNov 19th 2014
     
    No. for that you need a white hole.
    • CommentAuthorLakes
    • CommentTimeNov 19th 2014
     
    Totally awesome pic!
    •  
      CommentAuthorpcstru
    • CommentTimeNov 19th 2014
     
    Posted By: Andrew PalfreymanWhat if, say, we construct a collapse into a black hole nested inside another one. Then when we cross the second, inner event horizon, does time go back to being boring and space likewise?

    There is only one event horizon - by definition. Even if you found two distinct singularities beyond that horizon, the effect would be the same, in the end as one. I think.

    I did wonder if the flow of time is because of the initial singularity acting like a inverse black hole, perhaps the universe will eventually cross over the event horizon at which point travel in another direction of time will become possible. I suspect this can't be so.

    I also wonder if spacetime is expanding, does that mean that a co-ordinate inside an event horizon can pass out, because the expansion of spacetime kind of pushes it out. I think this is more plausible.

    But it all has a little whiff of woo.
    • CommentAuthorbr
    • CommentTimeNov 19th 2014
     
    Posted By: pcstruEven if you found two distinct singularities beyond that horizon,
    which I'm sure is possible, temporarily, as two black holes merge. Weird thought.

    Which leads to another strange thought. Imagine floating in space at a safe steady distance watching a black hole. Now imagine another black hole of the same mass hurtling towards it at a considerable fraction of the speed of light. In the case of a direct hit, I guess you would get one black hole traveling away from you at half the speed of light (give or take a relativistic correction). But there would be no fragments or explosion, just a quiet hurtling.
  12.  
    The details of the collision would appear frozen on the shared event horizon. And so it would look like a crash in slow motion, except that it would be so slow that the collision would last forever, for all intents and purposes

    I think.
    • CommentAuthorbr
    • CommentTimeNov 20th 2014 edited
     
    Posted By: Andrew PalfreymanThe details of the collision would appear frozen on the shared event horizon. And so it would look like a crash in slow motion, except that it would be so slow that the collision would last forever, for all intents and purposes.
    but what about conservation of momentum, where does that go? I should be able to answer the question myself, but would take a while.

    edit: easy enough, just consider the centre-of-mass frame. In such a frame, the BHs will collide and come to a stop. In the observer frame, it will be as I described. Also, BH collisions don't look like they last forever, the event horizon expands to engulf them in finite external observer time. See simulations for example https://www.youtube.com/watch?v=GVds0q0y5RM which I imagine take time dilation near the horizon into account.
  14.  
    Well, there is that.

    "Relativity Is Hard", says Barbie Andrew
    • CommentAuthorLakes
    • CommentTimeNov 20th 2014
     
    Relativity is relatively hard?
    •  
      CommentAuthorpcstru
    • CommentTimeNov 20th 2014 edited
     
    Whatever happened to Overtime.

    Which echos my own thoughts that people who work too hard are damaging the economy.
  17.  
    Now I'm relatively depressed.
    • CommentAuthortinker
    • CommentTimeNov 20th 2014
     
    My thought for the day concerns members of the old Steorn forum no longer with us. David Archibald, a tragic and accidental death by drowning, Blake Walston - cancer, and just this week Rick Keefer. Nice guys all.
    •  
      CommentAuthorpcstru
    • CommentTimeNov 20th 2014
     
    Ol Blake I'm familiar with - but the others - who were they?
    • CommentAuthortinker
    • CommentTimeNov 20th 2014
     
    Quieter than some perhaps, but members all the same. DA was an electronics technician at Heriot-Watt School of Engineering, and RK was a Missisipian and former Air-force Radar specialist.

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