mersenneforum.org  

Go Back   mersenneforum.org > Extra Stuff > Science & Technology

Reply
 
Thread Tools
Old 2006-05-13, 16:48   #1
mfgoode
Bronze Medalist
 
mfgoode's Avatar
 
Jan 2004
Mumbai,India

22×33×19 Posts
Lightbulb Speed of light


Slowing down light used to be considered a
neat trick for physics wonks. But researchers in New York now say
[0]they've pushed light into reverse. And as if to defy common sense,
the
backward-moving light travels faster than light." While there's not
much
use to come of it yet, it will be interesting if Einstein himself is
proved wrong.
This strenghtens my belief that the speed of light is infinite, but the limiting speed of interaction is 'c'

http://www.scienceblog.com/cms/light...rds-10590.html

Mally
mfgoode is offline   Reply With Quote
Old 2006-05-14, 12:50   #2
TTn
 

3×1,901 Posts
Default

These things have been theorized for awhile I thought.
While a particle cannot travel faster than the speed of light, it can bump other particles ahead of it's own path, so that the observer sees this illusion as faster than c travel.

Quote:
Einstein said information can't travel faster than light, and in this case, as with all fast-light experiments, no information is truly moving faster than light," says Boyd. "The pulse of light is shaped like a hump with a peak and long leading and trailing edges. The leading edge carries with it all the information about the pulse and enters the fiber first. By the time the peak enters the fiber, the leading edge is already well ahead, exiting. From the information in that leading edge, the fiber essentially 'reconstructs' the pulse at the far end, sending one version out the fiber, and another backward toward the beginning of the fiber."

Mozart was the first faster than light transmission, through a brass medium.

Last fiddled with by TTn on 2006-05-14 at 13:01
  Reply With Quote
Old 2006-05-14, 22:11   #3
Xyzzy
 
Xyzzy's Avatar
 
"Mike"
Aug 2002

174608 Posts
Default

If I am in a car travelling at the speed of light, and I turn my headlights on, what happens?
Xyzzy is offline   Reply With Quote
Old 2006-05-14, 23:10   #4
biwema
 
biwema's Avatar
 
Mar 2004

38110 Posts
Default

Quote:
Originally Posted by Xyzzy
If I am in a car travelling at the speed of light, and I turn my headlights on, what happens?
you cannot drive at the speed of light.
if you drive at speed of light - 1km/h, the light from your headlights travels 1 km/h relative to the car. Due to the speed of the car your time runs so slow that you have the feeling that the light from your headlights has the speed of light.
biwema is offline   Reply With Quote
Old 2006-05-14, 23:23   #5
biwema
 
biwema's Avatar
 
Mar 2004

5758 Posts
Default

thoughts...

- I assume that the light has not speed of light but epsilon (very very small amount) less than that speed where the kinetic energy of a mass reaches infinte.

- Black holes are not that black. Light always can exit but its frequency goes asymptotic to zero when the mass of the black hole increases. A mass falling into the black hole will not rech the speed of light, either. The frequency is so close to zero that nothing can be observed, but still there is no blackshield horizon or so.
biwema is offline   Reply With Quote
Old 2006-05-15, 01:32   #6
jinydu
 
jinydu's Avatar
 
Dec 2003
Hopefully Near M48

2·3·293 Posts
Default

Quote:
Originally Posted by biwema
if you drive at speed of light - 1km/h, the light from your headlights travels 1 km/h relative to the car. Due to the speed of the car your time runs so slow that you have the feeling that the light from your headlights has the speed of light.
Not true. From your frame of reference, the light from your headlights still travels at 299,792,458 m/s. It is a postulate of special relativity (and a consequence of Maxwell's equations) that the speed of light is the same in all inertial frames of reference.

And also, time does not run slow for you in your frame of reference. After all, in your frame of reference, you are at rest.

In any case, the phrase "If I am in a car travelling near the speed of light" is misleading because all speeds are necessarily measured in a particular frame of reference, and there is no universal frame of reference.

Quote:
Originally Posted by biwema
- I assume that the light has not speed of light but epsilon (very very small amount) less than that speed where the kinetic energy of a mass reaches infinte.
That is impossible. c is by definition the speed of light; and as pointed out earlier, special relativity postulates that this speed is always the same in every frame of reference. Furthermore, it can be shown that the speed at which the kinetic energy of a massive particle approaches infinity is exactly c.

All these conclusions (except the constancy of c, which must be either accepted as an axiom or derived from Maxwell's equations) can be derived mathematically; they are not just vague, qualitative, speculative ideas.

Last fiddled with by jinydu on 2006-05-15 at 01:42
jinydu is offline   Reply With Quote
Old 2006-05-15, 16:54   #7
philmoore
 
philmoore's Avatar
 
"Phil"
Sep 2002
Tracktown, U.S.A.

2×13×43 Posts
Default

Quote:
Originally Posted by jinydu
Not true. From your frame of reference, the light from your headlights still travels at 299,792,458 m/s. It is a postulate of special relativity (and a consequence of Maxwell's equations) that the speed of light is the same in all inertial frames of reference.

And also, time does not run slow for you in your frame of reference. After all, in your frame of reference, you are at rest.
Biwema was correctly describing what would be observed in a frame of reference with respect to which the car moves at slightly less than the speed of light. Obviously the existence of such a frame is implied by the original question. Jinydu is also correct in pointing out that the difference in velocity being 1 km/s and the time dilation are not what the passenger in the car sees, but what is observed in the frame in which the observations are made. There really is no contradiction here.
philmoore is offline   Reply With Quote
Old 2006-05-16, 04:48   #8
mfgoode
Bronze Medalist
 
mfgoode's Avatar
 
Jan 2004
Mumbai,India

205210 Posts
Lightbulb Speed of light.

Quote:
Originally Posted by Xyzzy
If I am in a car travelling at the speed of light, and I turn my headlights on, what happens?

A good question Mike and requires an equally good answer.

I tried to explain this phenomena but it is much too long to write it out.

First of all one must understand the theorem of the addition of velocities.
In Newtonian physics this is simply to add the two velocities. In Relativist physics the added velocities will always be less than the speed of light.
At slow speeds the effect cannot be noticed but at subliminal velocities the effect is appreciable.
No amount of explanations can cover this topic. The only resource is math equations which as you will see are not so difficult to follow and are quite elementary.
I give this URL as a first step to your question. From there on, there are several links to go onto.

http://www.bartleby.com/173/13.html

Mally
P.S. Read down till Equation A and Eqn.B and follow thru.

Last fiddled with by mfgoode on 2006-05-16 at 04:55
mfgoode is offline   Reply With Quote
Old 2006-05-16, 12:37   #9
alpertron
 
alpertron's Avatar
 
Aug 2002
Buenos Aires, Argentina

17·79 Posts
Default

There are other problems here:

* An actual passenger will need a year accelerating at 1g in order to reach relativistic speeds (and more years to reach (c - 1km/h)).

* From the speed the elemental particles in space crashes into your vehicle, you will see that it will be destroyed, much like the Columbia Space Shuttle on February 1st, 2003 when it converted into flames over Texas at an altitude of 63 km and a speed of 5.6 km/s (20000 km/h).
alpertron is offline   Reply With Quote
Old 2006-05-16, 16:52   #10
mfgoode
Bronze Medalist
 
mfgoode's Avatar
 
Jan 2004
Mumbai,India

22×33×19 Posts
Question speed of light

Quote:
Originally Posted by biwema
you cannot drive at the speed of light.
if you drive at speed of light - 1km/h, the light from your headlights travels 1 km/h relative to the car. Due to the speed of the car your time runs so slow that you have the feeling that the light from your headlights has the speed of light.
:surprised
Speed of light-1km/hr.? Alpertron uses the same value.
Am I missing something ?
Mally
mfgoode is offline   Reply With Quote
Old 2006-05-16, 17:01   #11
alpertron
 
alpertron's Avatar
 
Aug 2002
Buenos Aires, Argentina

53F16 Posts
Default

The speed of light is (by definition) 299792458 m/s.

1 km/h = 0.27777.. m/s

So c - 1 km/h = 299792457.72222 m/s = 1079252847.8 km/h

Where is the problem?
alpertron is offline   Reply With Quote
Reply

Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
First light xilman Astronomy 17 2018-10-08 22:15
Racism or low light levels or...? jasong jasong 2 2016-09-25 05:07
What if dark matter is actually light?(emitted light) jasong jasong 32 2014-01-04 07:50
Changes to the speed of light. Flatlander Homework Help 67 2011-01-22 13:37
Will we ever go faster than the speed of light? ixfd64 Science & Technology 7 2009-07-19 14:46

All times are UTC. The time now is 05:29.

Fri Mar 5 05:29:31 UTC 2021 up 92 days, 1:40, 0 users, load averages: 1.98, 1.88, 1.97

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, Jelsoft Enterprises Ltd.

This forum has received and complied with 0 (zero) government requests for information.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation.
A copy of the license is included in the FAQ.