From Wikipedia, the free encyclopedia

	Portal This article is within the scope of WikiProject Physics, which collaborates on articles related to physics.
Start	This article has been rated as Start-Class on the assessment scale.
Mid	This article is on a subject of Mid importance within physics.
Help with this template This article has been rated but has no comments. If appropriate, please review the article and leave comments here to identify the strengths and weaknesses of the article and what work it will need.

This article may be too technical for a general audience. Please help improve this article by providing more context and better explanations of technical details to make it more accessible, without removing technical details.

Maybe this page could be turned into a history of the ice cream cone. Here is a site to check for some data. [1] But probably the name of the article would be changed. Rednblu 04:33, 3 Sep 2003 (UTC)

Light cones don't have anything to do with ice cream; it's a general relativity thing. Whoever wrote the current version of the article was just making stuff up. —Paul A 04:39, 3 Sep 2003 (UTC)

Exactly. I am reviewing my relativistic mechanics notes to see if I could assemble a rough draft for us to improve. Rednblu 13:36, 3 Sep 2003 (UTC)

[edit] New version

I've made a few changes to this article. I want to make major changes to it though. I have a version in my sandbox which people can edit.---Mpatel (talk) 14:50, August 28, 2005 (UTC)

The biggest concern is to have another article on absolute future and absolute past, which are global concepts which should be contrasted with the light cone, which is defined at the level of tangent spaces.---CH (talk) 23:30, 14 September 2005 (UTC)

[edit] Can someone translate the page into english please?

Thanks. _{(Unsigned comment by 84.92.147.230 6 January 2006}

I agree with this comment. I'm trying to decipher some science fiction novels (1 2) that require thorough familiarity with the "light cone" concept to fully understand their plots. This article really isn't helping. 4.89.240.163 00:24, 26 February 2006 (UTC)

Well, I'm no physicist - but I think I have a layman's interpretation for you. Someone please correct if I am wrong. Imagine that you are floating in empty space and that you have just set off a very bright explosion (some kind of super firework). The light from this explosion will take time to propagate throughout the universe. Another person floating 1 light year away will not see your explosion for one year. However, a person only one-half light year away will only need to wait for one-half year. A person only one-quarter light year away waits only one-quarter year, and so on and so forth. You can see how the gradual and symmetric nature of time and distance forms a 4 dimensional cone (which actually looks to us like an expanding sphere) - this is the future light cone, because these other floating observers will see your explosion in the future.

Now the past light cone might work this way. Imagine that you are again floating around in your empty space with your explosive device and you want to set it off. There is just one problem, you can't set your explosion off until you see someone else's explosion first (perhaps this is a game - things can get boring in empty space). So you wait and watch the empty skies until you see a bright explosion. Hooray! Now you can set off your own explosion. But a question, how far away was that explosion you just saw? If it was 1 light year away, then that means that guy set his explosion off 1 year ago. You had to wait an entire year before you saw it and could set off your explosion. But if you were closer you would have waited a shorter time. Imagine if his explosion was set off 1 million light years away, you would be sitting there pretty bored with your firework for a very long time!

You can imagine someone moving away from you at the speed of light. This person will never see your explosion, and thus can never be within your future light cone. Conversely, an old explosion set off somewhere very distant will been seen by you long after you saw an earlier explosion and already set off your own device. You might not even see this ancient explosion until long after the game has become boring and everyone within 100 light years doesn't play anymore. This ancient explosion long missed it's chance to effect the game, and thus is outside of your past light cone.

In these examples the explosions and reactions represent spacetime events and the causal influence they exert upon each other.

I hope Einstein is not turning in his grave at my simplistic interpretation.63.192.52.26 22:49, 4 January 2007 (UTC)

I think the simplest way to put it is that Einstein posited that Light is an absolute speed and nothing can go faster then light. Since nothing can go faster then light anything we DO (or rather, any EVENT) cannot effect anything outside of your light cone (the speed of light times the time which has passed since the event). So an explosion a million light years away will not effect us immediately, only once our position (time AND space) has been enveloped by the light cone can we be effected by the light from the explosion). Everything works at light speed or LESS then light speed, so any effect on one thing from another must reside within this cone of space and time. Gelsamel 17:13, 27 August 2007 (UTC)

[edit] Volume of the Light cone

The volume of the light cone should be mentioned as (1/3)*pi*r^2*h whereas the one-third is relational to clopen conditions. —Preceding unsigned comment added by 24.22.111.99 (talk) 04:21, August 29, 2007 (UTC)