# The Naked Scientists Forum

### Author Topic: Light And Time And Space, Arrives Before It Leaves?  (Read 1537 times)

#### Titanscape

• Hero Member
• Posts: 785
##### Light And Time And Space, Arrives Before It Leaves?
« on: 04/07/2009 07:32:28 »
Light travels at the speed of light of course, but then can it arrive at a point before it leaves, or even near the point of origin?

Is it possibly in many places at the same point of time, or at least from it own perspective, since time stands still from it's position?

#### LeeE

• Neilep Level Member
• Posts: 3382
##### Light And Time And Space, Arrives Before It Leaves?
« Reply #1 on: 04/07/2009 19:57:44 »
It is widely assumed that no time passes for light in accordance with relativity.  However, since we don't actually know what light really is beyond its behaviour i.e. it's structure etc, it's a bit of a dodgey assumption to make imo.

Working on the basis that the assumption is true though, then the light will experience nothing as no time will pass for it to experience anything within.  From it's seemingly static point of view though, it would seem to be simultaneously everywhere that it has been, which gets confusing because you then end up trying to define a state that is both simultaneously static and dynamic

Consider a ray of light that is emitted from a light source on one side of 10 m wide room and is absorbed by the other wall.  Just after it has been emitted, and traveled, let's say a few centimetres, it's static view of the world (static because no time can pass) can only incorporate the distance it has traveled, but after it's reached half way across the room it must be able to incorporate it's extra travel.  However, from it's point of view, as no time can have passed, nothing could have changed (that static view again).

The easiest solution to this, and implicit in relativity, is that the combined vectors for movement through space and movement through time always sum to 'c'.  Everything then, is always traveling at 'c' through space-time.  It doesn't matter how many spatial dimensions you're traveling through because all the spatial movement vectors can be summed to a single vector, but it seems as though one dimension is always reserved for the temporal dimension.  It's possible then, that time does pass for light and from it's point of view it believes it is actually stationary; it just sits there and watches the world change around it.

A consequence of the apparent summed vector nature of movement through space-time is that there do not appear to be any other types of dimension involved.  If you sum three vectors at right angles to each other, instead of just the two we're aware of (spatial & temporal), you get different results that don't appear to match reality.  If you work with just two vectors at right angles everything can be mapped within a circle but adding a third right-angled vector raises this to a sphere.  For any two summed vectors you identify a unique point on the circle's perimeter but adding a third means that the summed point can lie anywhere along a line from that point to the center of the circle/sphere; we don't see this.

#### The Naked Scientists Forum

##### Light And Time And Space, Arrives Before It Leaves?
« Reply #1 on: 04/07/2009 19:57:44 »