## Backward Time???

Safer than Professor Rex's office hours
19683
Posts: 151
Joined: Wed Jun 05, 2013 12:15 pm

### Backward Time???

On bonus level 40, if you go to the top right corner of the screen and accelerate to the right, the bullets going from left to right go backwards back into the cannon! Since the raptor is accelerating, it is not an inertial frame, but this still seems impossible. I know that relativity can slow down and speed up time, but can it go backwards?
Binomial Theorem: ((a+b)^n)= sum k=0->k=n((n!(a^(n-k))(b^k))/(k!(n-k)!))

testtubegames
Site Admin
Posts: 1078
Joined: Mon Nov 19, 2012 7:54 pm

### Re: Backward Time???

Crazy, right?

You can see the same effect with the clocks - as you move around some clocks (especially those far away from you) can tick backwards. When I first saw that as I was developing the game, I had the same reaction. Is this a bug? What's going on?!

Turns out, that *does* happen. But it doesn't mean anything is actually going back in time. You are (I hope!) playing in the 'Measured View', which means that, basically, it's assumed that light is moving from a clock/bullet towards your eyes at infinite speed. You're seeing everything at that 'instant' - without having to wait for its light to reach you. Which leads to a couple points:

1) You wouldn't see this in the 'Seen' view, where you only see an object / event when its light reaches you. In the real world, we'll never witness something moving back in time. (Phew. Causality preserved.)
2) The 'Measured View' time you'd see measure on a given clock, say, depends on whether you're moving towards or away from it. So if you change your direction quickly, a clock's time can change abruptly, even back in time. For a cool thought-experiment about this fact, check out the Andromeda Paradox.

19683
Posts: 151
Joined: Wed Jun 05, 2013 12:15 pm

### Re: Backward Time???

So maybe we must consider the 'seen' view to be closer to reality and the 'measured' view to be sort of imaginary. Because the measured view ignores the finite propagation of light, it lets information travel faster than light. It uses the effects of relativity while completely ignoring the basic premise, which is that light, matter, and information travel at a finite speed.
With the Andromeda paradox, it seems like as far as the people on Earth are concerned, the invasion was decided 2.5 million years ago, when it became too late for information to get from Earth to Andromeda in time. Although it is purely philosophical.
Binomial Theorem: ((a+b)^n)= sum k=0->k=n((n!(a^(n-k))(b^k))/(k!(n-k)!))

testtubegames
Site Admin
Posts: 1078
Joined: Mon Nov 19, 2012 7:54 pm

### Re: Backward Time???

19683 wrote:So maybe we must consider the 'seen' view to be closer to reality and the 'measured' view to be sort of imaginary
In a way, yes. 'Measured' involves you basically just *knowing* what's going on and reconstructing it. Not nearly as natural. But very useful, since that's generally how we think of reference frames in SR.

For instance, when we talk about such fundamental parts of SR as Length Contraction and Time Dilation... those are discussed in the measured view. Not the seen view. (It's framed in terms of using chalk, or rulers, or light pulses to measure the length of something. Not just 'looking' at it.) It's a lot easier and a lot more illuminating to the science to do so. But that distinction is rarely made entirely clear.