Register | Sign In


Understanding through Discussion


EvC Forum active members: 65 (9162 total)
4 online now:
Newest Member: popoi
Post Volume: Total: 915,815 Year: 3,072/9,624 Month: 917/1,588 Week: 100/223 Day: 11/17 Hour: 0/0


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
Author Topic:   Black Holes, Singularities, Confusion
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 46 of 60 (352311)
09-26-2006 6:19 AM
Reply to: Message 37 by Brad McFall
09-23-2006 10:19 AM


Re: more Questions..
Worm holes etc were science fiction enough for me not to go further than a cursory interest in Penrose, etc. until I heard by how much a Romance Studies Professor at Cornell was intriqued and enamoured of Hawking's book on Time. I do need to catch up on some ideas in physics.
I'd certainly recommend it, Brad. I'm sure you'll love it. Hawking's 'Brief History...' and 'Universe in a Nutshell' are both well worth a good read, as in Brian Greene's book. If fancy some maths (and I mean reall maths!), try Penrose's 'road to reality'.
Have fun!

This message is a reply to:
 Message 37 by Brad McFall, posted 09-23-2006 10:19 AM Brad McFall has replied

Replies to this message:
 Message 53 by Brad McFall, posted 09-26-2006 5:04 PM cavediver has not replied

  
Ender
Junior Member (Idle past 6281 days)
Posts: 18
From: Covington, Georgia
Joined: 08-04-2006


Message 47 of 60 (352346)
09-26-2006 10:12 AM


"Naked" singularity
In my interest in this subject I've come across several references to "Naked" singularities or regions of space-time with infinite density that aren't surrounded by an event horizon. I was wondering if these are still considered feasible by physicists.
If so how would that be possible?
Thanks!

Replies to this message:
 Message 48 by 1.61803, posted 09-26-2006 10:19 AM Ender has not replied
 Message 49 by 1.61803, posted 09-26-2006 10:25 AM Ender has not replied
 Message 51 by cavediver, posted 09-26-2006 11:15 AM Ender has not replied

  
1.61803
Member (Idle past 1503 days)
Posts: 2928
From: Lone Star State USA
Joined: 02-19-2004


Message 48 of 60 (352348)
09-26-2006 10:19 AM
Reply to: Message 47 by Ender
09-26-2006 10:12 AM


Re: "Naked" singularity
I think you just described a black hole.

This message is a reply to:
 Message 47 by Ender, posted 09-26-2006 10:12 AM Ender has not replied

  
1.61803
Member (Idle past 1503 days)
Posts: 2928
From: Lone Star State USA
Joined: 02-19-2004


Message 49 of 60 (352349)
09-26-2006 10:25 AM
Reply to: Message 47 by Ender
09-26-2006 10:12 AM


Re: "Naked" singularity
ender writes:
If so how is this possible?
R=2GM/c2

This message is a reply to:
 Message 47 by Ender, posted 09-26-2006 10:12 AM Ender has not replied

Replies to this message:
 Message 50 by cavediver, posted 09-26-2006 11:08 AM 1.61803 has replied

  
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 50 of 60 (352359)
09-26-2006 11:08 AM
Reply to: Message 49 by 1.61803
09-26-2006 10:25 AM


Re: "Naked" singularity
R=2GM/c2
Only for Scwarzschild geometry, young Padawan

This message is a reply to:
 Message 49 by 1.61803, posted 09-26-2006 10:25 AM 1.61803 has replied

Replies to this message:
 Message 52 by 1.61803, posted 09-26-2006 12:16 PM cavediver has not replied

  
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 51 of 60 (352361)
09-26-2006 11:15 AM
Reply to: Message 47 by Ender
09-26-2006 10:12 AM


Re: "Naked" singularity
Hi Ender, geat question
Principally, NS occur in two situations: possibly as the end-state of Hawking Evaporation of an astrophysical (but microscopic) black hole; and as part of the parameter space of (i.e. one version of) the non-trivial black holes, such as Reisnner Nordstrom (charged), Kerr (spinning), Kerr-Newman (spinning AND charged) or some of the string theory inspired variants.
The first case occurs because the mass of the black hole is reducing owing to Hawking Radiation. This reduces the size of the Horizon (via that bit of maths helpfully provided above). The evaporation rate is runaway - the smaller the black hole gets, the hotter it gets, the faster it evaporates, etc, etc. Eventually the horizon and singularity coalesce, and... we don't know. Maybe a bang (gamma-ray burster?), maybe a sniffle, maybe nothing left, maybe a naked singularity. It will take a lot more knowledge of quantum gravity before we know, but string theory provides some clues.
I'll come back to the second case in a while.

This message is a reply to:
 Message 47 by Ender, posted 09-26-2006 10:12 AM Ender has not replied

  
1.61803
Member (Idle past 1503 days)
Posts: 2928
From: Lone Star State USA
Joined: 02-19-2004


Message 52 of 60 (352386)
09-26-2006 12:16 PM
Reply to: Message 50 by cavediver
09-26-2006 11:08 AM


Re: "Naked" singularity
Yes "master"...but my feable attempt to google:
"Naked black hole" led me down a path to the dark side of internet pornography. much I have to learn.

This message is a reply to:
 Message 50 by cavediver, posted 09-26-2006 11:08 AM cavediver has not replied

  
Brad McFall
Member (Idle past 5032 days)
Posts: 3428
From: Ithaca,NY, USA
Joined: 12-20-2001


Message 53 of 60 (352437)
09-26-2006 5:04 PM
Reply to: Message 46 by cavediver
09-26-2006 6:19 AM


Re: more Questions..
Gladyshev had tried to relate "Penrose" to his ideas on how "math" relates between macrothermodynamics (linearly) and quantum mechanics.
I was tempted to take on that road but I have tended to think older texts like Dirac's would do better for me. I have a very curious idea about "microtubules" and "the central dogma of molecular biology" which is independent of Penroses' and it is probably that rather that kept me from buying "The Road to Reality." Thus, I already recognized that no matter what "road" denoted It was already some actual road and thus I would not learn that. The road was simply what Georgi wrote as "building" to me from Moscow.

This message is a reply to:
 Message 46 by cavediver, posted 09-26-2006 6:19 AM cavediver has not replied

  
Utopia
Junior Member (Idle past 5136 days)
Posts: 26
From: Boston, MA.
Joined: 09-19-2006


Message 54 of 60 (353656)
10-02-2006 2:47 PM
Reply to: Message 45 by cavediver
09-26-2006 5:08 AM


Re: Some pretty diagrams...
Thanks for your response. My question is why is the 45 degree angle the speed of light and not the horizontal? I was under the impression that light traveled purely through space and not at all through time (meaning a photon doesn't age)? At a 45 degree angle, where the vertical is time and the horizontal is space, it would suggest that light does in fact travel through time - and I didn't think that was possible.
Greg P.

This message is a reply to:
 Message 45 by cavediver, posted 09-26-2006 5:08 AM cavediver has replied

Replies to this message:
 Message 55 by cavediver, posted 10-03-2006 8:16 AM Utopia has not replied

  
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 55 of 60 (353833)
10-03-2006 8:16 AM
Reply to: Message 54 by Utopia
10-02-2006 2:47 PM


Re: Some pretty diagrams...
I was under the impression that light traveled purely through space and not at all through time (meaning a photon doesn't age)?
Ok, from the perspective of an external observer, light travels at c, about 300,000,000m/s. If we choose units where we measure time in seconds and distance in light-seconds (300,000,000m) and we draw one second as the same length as a light-second, we get the 45 degree line.
From the perspective of light, you are correct it doesn't age - but also it doesn't move either, because distance in the direction of travel has been Lorentz contracted to zero. This sort of makes sense... it doesn't age as it travels, but that's becasue it doesn't have to go anywhere! So no, even from the perspective of light itself, it doesn't think of itself as travelling "horizontally".
it would suggest that light does in fact travel through time
From our perspective, light does travel through time, it just does not age as it does so. There is more than one kind of time

This message is a reply to:
 Message 54 by Utopia, posted 10-02-2006 2:47 PM Utopia has not replied

  
1.61803
Member (Idle past 1503 days)
Posts: 2928
From: Lone Star State USA
Joined: 02-19-2004


Message 56 of 60 (355422)
10-09-2006 4:13 PM


The only purpose of time is so that everything does not happen all at once.
Energy is the currency of the universe, time is the ink and space is the paper it is printed on.

Replies to this message:
 Message 57 by jaywill, posted 10-28-2006 8:09 AM 1.61803 has not replied

  
jaywill
Member (Idle past 1941 days)
Posts: 4519
From: VA USA
Joined: 12-05-2005


Message 57 of 60 (359458)
10-28-2006 8:09 AM
Reply to: Message 56 by 1.61803
10-09-2006 4:13 PM


I thought Time is how we measure Motion through Space.
I thought Motion is the way we measure Space and Time.
And I thought Space is the way we measure Motion and Time.
These three are a triangle. Each is needed to give meaning to the other two. It is really a relativity matter.
What I have a hard time conceptualizing is the Curvature of Space.
Can anyone give a layman's level of assistance to conceptualize the curvature of space around matter? Assuming that it is true at the moment.
Is there a non physics explanation to help people understand how space (which I thought is nothing) could be curved?
Edited by jaywill, : No reason given.
Edited by jaywill, : No reason given.

This message is a reply to:
 Message 56 by 1.61803, posted 10-09-2006 4:13 PM 1.61803 has not replied

Replies to this message:
 Message 58 by nwr, posted 10-28-2006 9:52 AM jaywill has not replied
 Message 59 by cavediver, posted 10-28-2006 8:48 PM jaywill has not replied

  
nwr
Member
Posts: 6408
From: Geneva, Illinois
Joined: 08-08-2005
Member Rating: 5.1


Message 58 of 60 (359466)
10-28-2006 9:52 AM
Reply to: Message 57 by jaywill
10-28-2006 8:09 AM


Is there a non physics explanation to help people understand how space (which I thought is nothing) could be curved?
Will you accept a mathematics explanation?
"Curvature", as the term is used in relativity, is a mathematical term. It is defined in terms of the distance metric (as generalized to include time).
To illustrate, consider a cylinder (the surface, not the solid). On the cylinder, we would measure distances as the shortest path along the cylinder. Mathematically, the cylinder is flat, so not at all curved. This corresponds to the fact that you cut cut down along the cylinder, and open it up so that it is flat, and you could do this without changing any distances (not counting those where the shortest path crosses the cut-line).
Take out your atlas, and look at a Mercator projection map of the world. It is really an unwrapped cylinder. Think of it as a cylinder, with the left and right side taped together where they match. Now, let's suppose that we scrap our current way of measuring distance on earth. And, as a new distance metric, we use the old distance between the two places on the Mercator map. We could scale it, say one inch on the map = 100 miles on Earth. This will be a different distance metric than we ordinarily use. With this new metric, the north pole and the south pole will be an infinite distance away. With this new distance, the earth is flat.
When physicists talk about curvature of space (or space-time), the metric they are using is based on light travel. The distance between two points is determined by the time it takes for light to travel between them. This was adopted as the standard for distance, following the Einstein conclusion that the velocity of light is the same for all observers.
I hope that helps.

Compassionate conservatism - bringing you a kinder, gentler torture chamber

This message is a reply to:
 Message 57 by jaywill, posted 10-28-2006 8:09 AM jaywill has not replied

  
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 59 of 60 (359556)
10-28-2006 8:48 PM
Reply to: Message 57 by jaywill
10-28-2006 8:09 AM


To add to NWRs explanation...
Take a length of rope. Stand in the middle of a field and put a stake in the ground. Tie one end of the rope to the stake. Walk away from the stake paying out a length of rope, say 10 feet. With the rope taut, walk around the stake once, measuring the distance you walk. Compare your answer to what you would expect from C=2xPixR. It should match of course.
Try it again with 50 feet of rope, then with 1000 feet, then 10 miles, then 100 miles, and finally 1000 miles. What do you notice? Your measured distances start to deviate from the usual formula for the circumference of a circle. Why?
Of course, you are not dealing with flat circles. You are on the Earth's surface which is curved, and your deviations from the circle formula actully measure the curvature of the Earth.
Now repeat the exercise, but make the Earth your centre point, and move off into space to make your circle. You will experience the same effect, owing to the curvature of space generated by the Earth. You can't see this curvature as it is slight, but you can measure its effect. The effect is much more pronounced and easily visible around a black hole.
Rather than circles, you could draw triangles on the ground and measure the angles. Once your triangle become large enough you realise that the angles actually add to more than 180 degrees, revealing a positively curved ground. The same thing happens in space: you find that the angles of triangles with perfectly straight lines don't add up to 180 degrees.
Edited by cavediver, : Finally remembered how to spell taut - actually, the wife pointed it out

This message is a reply to:
 Message 57 by jaywill, posted 10-28-2006 8:09 AM jaywill has not replied

Replies to this message:
 Message 60 by GDR, posted 10-29-2006 1:46 AM cavediver has not replied

  
GDR
Member
Posts: 6202
From: Sidney, BC, Canada
Joined: 05-22-2005
Member Rating: 1.9


Message 60 of 60 (359582)
10-29-2006 1:46 AM
Reply to: Message 59 by cavediver
10-28-2006 8:48 PM


That's fantastic. Thanks

This message is a reply to:
 Message 59 by cavediver, posted 10-28-2006 8:48 PM cavediver has not replied

  
Newer Topic | Older Topic
Jump to:


Copyright 2001-2023 by EvC Forum, All Rights Reserved

™ Version 4.2
Innovative software from Qwixotic © 2024