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Author Topic:   Question About the Universe
Lurkey
Junior Member (Idle past 4078 days)
Posts: 11
Joined: 11-03-2012


Message 29 of 373 (678878)
11-11-2012 7:17 AM
Reply to: Message 26 by NosyNed
05-09-2009 9:55 PM


Re: Gravity
If there was another me on another earth just over the CH and he shot a satellite at me so that it outpaced my shrinking CH, would i eventually see it blue shift into existence (if i was very patient)?
Or would i never see the satellite because he just cannot chuck it fast enough?...like there is too much expanding universe between me and him 'pushing back' if you know what i mean.
EDIT: Sorry Ned, this is not a reply to your post....my bad...still learning the ropes!
Edited by Lurkey, : No reason given.

This message is a reply to:
 Message 26 by NosyNed, posted 05-09-2009 9:55 PM NosyNed has not replied

Replies to this message:
 Message 31 by Stile, posted 11-12-2012 3:15 PM Lurkey has replied

  
Lurkey
Junior Member (Idle past 4078 days)
Posts: 11
Joined: 11-03-2012


Message 33 of 373 (679610)
11-14-2012 6:24 PM
Reply to: Message 31 by Stile
11-12-2012 3:15 PM


Re: Cosmological Horizon
Thanks Stile
So that sounds reasonable. CH is a bit like earth’s.it’s all about where i stand.the horizon is real, but in a way its an artifact.
But then the satellite won’t ever catch up! & Ned’s comment:
The "speed of light" isn't comparable to a speed limit on a highway. It is a fact about the nature of the thing called spacetime.
Seems all^ makes the CH very real and physical. Like you’ve just defined the edge. There is no shift of position that will ever enable me to see over it (?!)Every star in a whole galaxy’s worth of galaxies could go supernova just over my CH, and it would make zero difference to me, ever.no matter what I did (?!)
Hey? Are we closed then? But its a horizon!!! If we’re in a pocket, then isn’t every other point in the universe in overlapping pockets? Don’t we shift from one pocket to another just by moving through our own pocket? Oh no! Lost again.
Say then you and I got together in the early days and each took one end of that rubber band and we glued the poor old ant to the middle..space has expanded since and we’re now over each other’s horizon.Is the band now infinitely stretched? What do you experience if I let go? Where is the ant?
Sorry if I’m being dense. It fascinates me, but cosmology is like a cupboard of horrors sometimes. You know, open the draw, shout with horror, slam the door shut again. Not the best way to learn, but to be fair you guys throw out some pretty full on things. A horizon that is coming to get me!
Anyways. Thanks for this too Stile, i WAS wondering:
Oh, and if you're wondering... the expansion of our universe (74.2 km/sec/Mpc) is about the same as:
2.4x10^-18 inches/sec/inch, or again written as:
0.000 000 000 000 000 002 4 inches/sec/inch
.
Take care,
Lurkey
....
EDIT: since posting, found this which helped a little:
http://www.mathpages.com/home/kmath666/kmath666.htm
One benefit of presenting horizons in a spacetime diagram, rather than in a purely spatial diagram, is that it makes clear the transitive nature of the partial ordering of events. In other words, if event b is inside the event horizon of event a, and if event c is inside the event horizon of b, then c is inside the event horizon of a. Lack of clarity on this point sometimes leads to confusion over the fact that galaxy C can be outside the horizon of galaxy A while it is inside the horizon of galaxy B, which is still inside the horizon of A. If horizons were purely spatial, this would seem to imply that C could send a signal to B, which could then relay the signal on to A, and hence C can send a signal to A, contradicting the fact that C is outside the event horizon of A. Needless to say, this reasoning is invalid, because it overlooks the fact that if C is outside the event horizon of A, then, even if B is presently inside the event horizon of A, by the time a signal from C reaches B, the latter must have passed outside of the event horizon of A.
Edited by Lurkey, : No reason given.

This message is a reply to:
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Replies to this message:
 Message 34 by Dr Adequate, posted 11-15-2012 5:47 AM Lurkey has replied
 Message 40 by cavediver, posted 11-15-2012 10:16 AM Lurkey has not replied

  
Lurkey
Junior Member (Idle past 4078 days)
Posts: 11
Joined: 11-03-2012


Message 41 of 373 (680343)
11-19-2012 7:53 AM
Reply to: Message 34 by Dr Adequate
11-15-2012 5:47 AM


Re: Cosmological Horizon
Thanks everyone
yeah CD, just by themselves all the names are confusing enough!
Physics tells us that there are limits to how much of the universe we can see and explore, and that even if we could travel at the speed of light we could only reach such-and-such a galaxy and no galaxy beyond it. And yet there is no edge.
No information flow. No casual contact. This just sounds so much like an edge!
But i know, i know... that's^ my problem. I think i'm making some headway but its taking me ages...one thing leads to another, you know?
Hopefully i'll get there one day.
By the way, I like the idea that the event horizon is our universe's ultimate light cone.
Also the whacky one where we're living in an inside out black hole
Hey and i'll cheer any extremely brave and patient person who cares to try and dumb this down for me:
http://ned.ipac.caltech.edu/...ineweaver/Figures/figure1.jpg

This message is a reply to:
 Message 34 by Dr Adequate, posted 11-15-2012 5:47 AM Dr Adequate has not replied

  
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