View Full Version here: : Absolute velocity
18-05-2011, 07:33 PM
Is the velocity of light the same in all directions in space? from Peter, the Ignorant Geologist.
18-05-2011, 07:58 PM
18-05-2011, 09:00 PM
Thank you Sarman. In 2006, data from an experiment measuring the one-way speed of EM (Electro-Magnetic) waves in a coaxial cable gave the speed of light as 300,000 +/- 400 +/- 20km/s in a measured direction RA(Right Ascension) = 5.5 +/- 2 hrs. Declination = 70 +/-10o S. This means that light ranged between speeds of 300,440 and 299,560 km/sec. There are similar results from other laboratories.
The ignorant Geologist.
18-05-2011, 09:00 PM
Yes....from Carl, the not so ignorant Geologist/Astronomer:):)
18-05-2011, 09:06 PM
Do you have a copy of the paper for this study??
18-05-2011, 09:59 PM
Reference below. I hope you understand the maths!! Wish I could
October, 2006 PROGRESS IN PHYSICS Volume 4
A New Light-Speed Anisotropy Experiment: Absolute Motion
and Gravitational Waves Detected
Reginald T. Cahill
School of Chemistry, Physics and Earth Sciences, Flinders University, Adelaide 5001, Australia
E-mail: Reg.Cahill@flinders.edu.au; http://www.scieng.flinders.edu.au/cpes/people/cahill_r/
The Ignorant one.
18-05-2011, 10:07 PM
Thanks. Just downloaded it.
19-05-2011, 09:59 AM
When the speed of light depends on its direction: (http://www.physorg.com/news/2011-05-when-the-speed-of-light.html)
Paper here. (http://prl.aps.org/abstract/PRL/v106/i19/e193003)
.. depends on the environment through which the light travels .. and 'space' is filled with EMFs .. the conditions/assumptions under which the question is framed, make all the difference.
19-05-2011, 10:13 AM
It was also measured in a gas, which would be far denser even than the dustiest and gassiest nebula. Despite its appearance space is not that full of gas and such. Not only that...how intense was the EMF they tested this under?? Space is full of EMF's but they're spread awfully thinly (remember the strength of a galaxy's average field)...how strong does it have to be before it starts affecting the velocity of the light traveling through it. As we've said ourselves countless times, it's one thing to get a measurement in a lab, an entirely different thing to measure it in "real" life.
19-05-2011, 10:42 AM
… measured at ambient temperature and pressure as follows:
Nothing too outrageous.
19-05-2011, 10:45 AM
Thank you CraigS. What is the Cassini probe and what will it tell us about this?
The Ignorant One.
19-05-2011, 11:18 AM
Nothing too outrageous for lab conditions but nothing like what the conditions are in free space. Do you realise how intense a 0.85T magnetic field is??? They're highly contrived conditions only meet or exceeded by, in the close proximity of white dwarfs or neutron stars.
19-05-2011, 11:46 AM
Methinks there's more behind your questions than the questions themselves, Ernest Wilson.
The Cassini-Huygens probe (http://en.wikipedia.org/wiki/Cassini_probe) is my favourite probe and is arguably, one of the most productive in recent times.
It has measured plasma-magnetic field interactions between Saturn and its satellites. The data it has produced is shaping our understanding of the magnetic environment surrounding Saturn. I am unfamiliar with any experiments designed to measure variations in the speed of light wrt directionality.
Are you aware of any such empirical data ?
19-05-2011, 07:50 PM
Let's not forget what the original question was. !!!!!!!!! In space.!!!!
I assume a vacuum. Duhhhh.
21-05-2011, 12:18 PM
Graig S. I have read that the Cassini Probe may be able to decide whether Lorentzian or Einstein Relavity should be the preferred reference. I assure you I am ignorant!
21-05-2011, 12:25 PM
Cool … do you have a reference for that ?
I'd be interested to read up on it !
PS: We're all ignorant of something .. (or most things not known … :) ).
22-05-2011, 11:32 AM
To answer the original question, no. By definition when you change the direction, the resultant velocity has changed.
But the speed of light in a vacuum is the same, regardless of direction.
22-05-2011, 11:44 AM
… Hmm two statements seemingly at odds with eachother ??… :question:
22-05-2011, 11:55 AM
They are....what does change is the velocity vector. However, with regards to light itself, the second statement applies, even when the velocity vector changes.
22-05-2011, 05:18 PM
Fascinating thread …
First .. the question (again) ...
The score so far:
- two "yeses";
- two "no's"
I hate tie-breakers, so put me down for:
- one "maybe" !
Any other takers ?
22-05-2011, 05:59 PM
Flip a coin:):P
22-05-2011, 06:04 PM
I noticed the term "Lorentzian Relativity" cropping up in an earlier post. So a more relevant question, is the measurement of the speed of light dependent on the motion of the observer? The answer is "absolutely" no.
The speed of light is the same in all directions.
23-05-2011, 09:22 AM
Carl is correct, Speed and Velocity are not the same thing. If you change direction then velocity by default changes even if the speed remains the same.
23-05-2011, 09:33 AM
The point I'm trying to make in this thread is that everyone is making different points which may be perfectly valid under different circumstances.
Steven clarified the question which, in my view, is the only way any clarity will ever come of statements made here.
Unless the question is worded with precision, little value will come of the thread. (Other than arguments).
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