[ExI] speed of light at the speed of light

[Norman Jacobs]

If there is no time, then light has no speed, so we can move at will
throughout the universe (to any position), unless we get sucked into a black
hole.

 

 

From: extropy-chat-bounces at lists.extropy.org
[mailto:extropy-chat-bounces at lists.extropy.org] On Behalf Of Anders Sandberg
Sent: Thursday, August 22, 2013 4:29 PM
To: extropy-chat at lists.extropy.org
Subject: Re: [ExI] speed of light at the speed of light

 

On 22/08/2013 20:58, John Clark wrote:

On Thu, Aug 22, 2013 at 7:29 AM, Gordon <gts_2000 at yahoo.com> wrote:

 

> I am in a spaceship accelerating away from earth and approaching the speed
of light. I have a flashlight. My instruments tell me that the light emitted
from my flashlight travels at c. This is true no matter whether I shine it
forward in the direction of my travel or backward toward the rear of the
ship. 

I am accelerating away from earth such that my ship's velocity relative to
earth compared to c is halved in each time period. For example at time t, my
ship is travelling at 90% of c. At t2, my ship is travelling at 95% of c. At
t3, my ship is travelling at 97.5% of c, and so on for an infinite amount of
time as I approach c.

 

It's OK for thought experiments to be wildly impractical but they must be
physically possible, and the above experiment would not only take an
infinite amount of time to perform it would also take an infinite amount of
energy.


However, the conclusion about infinite time and energy are a *result* of
doing the Einstein thought experiment properly. You cannot dismiss the
lightspeed case straight away.

Einstein had a nifty way of showing that there is something problematic
going on in this case, which I think was one of his primary reasons for
developing the full theory: suppose you run past an electromagnetic wave
while travelling at c. What do you see? It ought to be static in your
reference frame, but in that case it breaks Maxwell's laws. So either
electrodynamics is wrong, or the velocity addition formula is wrong (and we
already have some suspicions since light seem to move at c regardless of
speed). So let's see what happens if we assume the velocity addition formula
has to be something else...




-- 
Anders Sandberg,
Future of Humanity Institute 
Oxford Martin School 
Faculty of Philosophy 
Oxford University 
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