Space Elevator

Go Japan! They always build the coolest things. I hope this works out because it would be awesome.

Sweet.

Don't read the comments if you know anything about physics or engineering, they will make you cry. And if you do not know anything about such things, also don't read them because they will corrupt your mind with incorrect information.

Example:

"The space elevator will not be cheaper than conventional means of accessing space because you will need massive amounts of fuel to keep the tension on the cables. Also we must remember the earth rotates on its axis, and this will cause the cables to act like a giant whip."

Alen Braxx, Jersey City, America


Why do people insist on pushing their opinions on others when they clearly know nothing about the subject under consideration?

The Relativity of Simultaneity

Ok kiddies, I am here today to educate on the topic of the Relativity of Simultaneity, in response to the confusion that seems to have arisen. I will admit firstly that the question (see ricks blog, tho I guess I will restate it here) is worded in a slightly confusing way, although I think it is unambiguous (edit: since getting to the end of this, I have decided it IS in fact ambiguous).

The problem is this:



I suppose I should first mention that all this is based on the fact that the speed of light is the same for all observers (we only need worry about non-inertial (non-accelerating) frames for this problem).
My illustrated solution to this problem is shown below, and I shall take you through it here. Note my train is moving very relativistically for emphasis, looks like >0.6c. When they say "Fred observes Alan and Bob to strike matches simultaneously when he is directly opposite Nancy", I put to you that this means "When Fred and Nancy occupy the same spacetime coordinates (approximately, tho I think it is only important that their "x" coordinates (direction of motion) match. Let us not worry about this slight confusion, say they are in the same place. Lets say Fred gives Nancy a high-five out the window at 0.6c) then the light from Alan and Bob striking matches at some time in the past reaches Fred. He concludes that, since he is in the centre of Alan and Bob, and none of them have moved anywhere for a long time, that they must have struck those matches simultaneously. In my diagram this is labelled "Fred's frame" and I have included a spacetime diagram to assist understanding. The yellow lines represent the light cones emanating from each match-lighting event while the red lines are the world-lines of Alan and Bob, i.e. their spacetime path. Note we don't even really care what Nancy is doing in this frame.

So, we now move to Nancys frame. To her, the train flys past at incredible speed. Since in the fourth frame she occupys the same spacetime coordinates as Fred she must observe the same thing as him, or rather any light that is reaching Fred must reach her also. So in a sense, she would "see" both matches being struck simultaneously also. She then remembers that light takes some time to reach her so she tries to figure out what time in the past those matches must have been struck. Because of the motion of the train, she (correctly) concludes that the trailing match (Alan) must have been lit first because the light had a greater distance to travel to reach her. Thus Fred and Nancy come to different conclusions about the simultaneity of the match-striking and the screwiness of relativity is manifest. And they are both right.



So, looking back at the options in that question, I guess I have to say D, because she does "see" both matches struck at the same time. Those answers are fairly misleading tho, because she would not conclude from this observation that those things had in fact happened at the same time. Also from my diagram it does kind of look like if she is far away in the y direction then she will in fact see the light from A first. I guess that makes sense, imagine she is a light-year away in the y-direction (vertical in my diagram, we can determine when she was 'opposite' Fred through some clever timing tricks) The Lorentz transformations don't care about the y direction so the events happen just the same. The distance between events would be small though because she is so far away, so really it's just like two light pulses come from the same place, so if A happened first in her frame she will see it first. So, thats my answer; if you assume they are close, she sees them simultaneously. As soon as she is displaced in the y direction a bit she will see the light from A first, with the delay between the light from each event increasing as one increases her distance in the y direction.

Also I haven't mentioned length contraction or time dilation, but those aren't really important for this problem. The train would be shorter in Nancys frame and the guys would seem to strike their matches more slowly to her than Fred would think, but nothing else changes.


If there is some flaw here let me know, but I'm pretty sure I'm right. We could actually calculate some stuff if we liked.

Ok so I got bored and calculated some stuff:

You know what we have to do

Marshmallow gun

Bahhaha.