If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I am reading the book SpaceTime and I have some questions for those that think they can answer in a coherent manner. It is not that I don't understand (well, some things I don't), but I am hoping I can get a clearer answer.
For example, if light does not escape from a black hole, does the photon actually stop moving and hence the speed of light at the horizon is zero or does the wavelength just expand to a frequency of zero? If the latter, does the photon keep moving forward?
Another question: if one is holding a mirror in front of himself and is running at the speed of light does the reflection disappear or again does the wavelength shift?
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
For example, if light does not escape from a black hole, does the photon actually stop moving and hence the speed of light at the horizon is zero or does the wavelength just expand to a frequency of zero? If the latter, does the photon keep moving forward?
Actually EM wave falling into a hole increases it's frequency (but speed is unchanged), until it hits the horizon and gets ultimately added to black hole's mass. See gravitational red and blue shift:
Gravitational time dilation counters this so we can't see frequency change if we are riding the photon (but it can be seen from a distance for example).
Another question: if one is holding a mirror in front of himself and is running at the speed of light does the reflection disappear or again does the wavelength shift?
You can imagine a bunch of things 'going wrong' when you reach speed of light, time is stopped, your mass is infinite, so the mirror thing could be imagined rather artistic.
Wavelength of light in front of you would be 'infinite' ,as your speed is equal to c, your mass is infinite and you have stopped the time (things that are pretty impossible in our plane of existence).
Conbining all that I guess you won't be able to see anything in the mirror...
Registered Member #175
Joined: Tue Feb 14 2006, 09:32PM
Location: Sudbury, ON
Posts: 111
The speed of light in and around a black hole is always 3*10^8 m/s, same as everywhere else (barring density issues, and rounding up.) So what happens? Look at it with from the particle perspective; ballistic trajectory, decayed orbits , that stuff. And yes, or so the theory goes, there is going to be a 'light sphere' just in or around the event horizon, where space curves such that the photons have a stable orbit around the black hole.
For the second question, you can't go at the speed of light... so let's imagine you're holding the mirror in front of you, and going at .99999999c. So, does the wavelenth shift? Nope. You and the mirror are in the same frame of reference, so your reflection will appear AS NORMAL. Behind you, on the other hand... redshift galore, and all the other fun optical abberations expected from such speeds.
Registered Member #65
Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155
Black hole theories upset many people’s notions – personally I think Hawking’s theories may show some odd correlations and contradictions. However in classic terms the entire earth could only form a theoretical black hole with a radius of about 8.86mm as R=(2GM)/c^2.
In terms of Einstein’s ideas, the classic light clock problem may be illuminating.
Ultimately people like to hang on to traditional models even if they may be subject to deemphasis in mainstream theoretical sciences.
Registered Member #29
Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500
One of those contradictions, elucidated by Stephen Hawking, is that black holes not only absorb matter and radiation, but emit radiation and matter as well. If I remember correctly, there are two mechanisms at work....
1. Blackbody radiation. The black hole has a "temperature" and emits radiation characteristic of blackbody radiation. In the coordinate frame near the event horizon, the photon could look like a gamma ray, but by the time it "climbs" out of the BH gravitational well, it is redshifted into the IR of mm-wave band. Hence, the BH, over time, will lose mass and "evaporate" when it falls below its critical mass. There's no escaping the Second Law of Thermodynamics! ;)
2. Virtual particle/antiparticle pair generation. Near the event horizon, particle/antiparticle pairs can be spontaneously generated. One is swallowed up by the BH and the other is ejected into some type of orbit around the BH.
I love studying modern physics, but unfortunately many of the papers that I've seen in the modern literature are heavy on arcane mathematical treatment and light on understanding... Or maybe I'm just a bit slow and fossilized!
wrote ...
Another question: if one is holding a mirror in front of himself and is running at the speed of light does the reflection disappear or again does the wavelength shift?
You will see no change in your reflection if you are running along a line that passes through you and the mirror, because for you and the mirror, light always travels at speed c. And you will never be able to reach speed c.
Registered Member #193
Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022
He gets to the end of the first paragraph before saying something completely wrong. "if we couldn't see vibrations of electron energy, the moon would be completely unnoticed. " What? no tides? I stopped reading there.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
gravityboy wrote ... The Raisin bread model of expansion is also a farce, it can't expand because if the universe were a loaf, it would have to be an infinite sized loaf, or an infinite amount of loaves with no room left to expand.
I think his head got stuffed with an infinite sized loaf that left no room for brains.
I'm wary of any theory that tries to describe the fundamental structure of the universe in terms of everyday objects like loaves of bread and dodecahedrons. Everyday objects exist entirely inside the structure of the universe, so you can't make a theory of the structure of the universe out of them, any more than you can make pi by adding integers together, or make the Haynes manual for your car out of the parts of your car.
A good theory of the universe would have to be made out of something finer and more abstract than material objects. Einstein made his theory of relativity out of thought experiments, and pure thought is pretty fine stuff. You don't need any mathematics at all to understand it though: all you need to take on board is that the speed of light always measures the same no matter where you are or how fast you're travelling.
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
relativity and stuff
