Re: Question about light clock and derivation of time dilation


"YBM" <ybmess@xxxxxxxx> wrote in message
news:42d3b85e$0$30231$636a15ce@xxxxxxxxxxxxxxx
> Androcles a écrit :
>>>>How can you confuse an event in the past with a vector?
>>>
>>>Technically speaking, space-time can be represented by
>>>an affine space, not a vectorial one :
>>>
>>>http://mathworld.wolfram.com/AffineSpace.html
>>
>> How can you confuse an event in the past with a vector?
>
> An event in the "past" (it's better to say "which happened
> before the arbitrary origin of a frame's clock") is very
> well represented as a (x,y,z,t) vector where t<0.

An event in the past is described by a coordinate (x,y,z,t),
not a vector. How can you confuse a coordinate with a vector?
I do know how. It's because they use the same notation.
That's how you can be confused and ARE confused.

>
> The event is not, technically speaking a vector,
That's right. A coordinate is not a vector.


but is
> represented by the vector of its coordinates.
Ah... you almost have it. A coordinate (x,y,z,t) is not a
vector (x,y,z,t)



> Did you remember
> geometry you've been teached in school ?

Better than you.
BTW, the past tense of "teach" is "taught", not "teached".
English can be difficult, I know, and since it isn't your first language
I won't hold it against you. You are doing quite well.
Now to brush up your math skills...


> Points in the euclidean
> plane have a vector of coordinates (x,y), *but* this plane
> is not a vector space.


Check out the bold text in math text-books, used for vectors.
http://en.wikipedia.org/wiki/Vector_space
Time is NOT a vector.


>
> To be more precise, it is not about the word "yesterday",
> but about the expression "the day before" you're claiming
> has no meaning (as well as "the day after").

To be more precise, there is no vector to yesterday.
>
> There no such thing as the "present" in space-time representation,

There is no such animal as "spacetime", the present is real enough, as
is the passage of time. "Spacetime" exists only in your imagination and
doesn't represent the physical world in which we exist. I'm not
interested in representing spacetime, this is a physics newsgroup, not a
math newsgroup.



> there is a set of events, and for any event and any frame of
> reference there are sets of simultaneous events, past events and
> future events.
>
>>>>>closing velocity and relative velocity (what you
>>>>>do for years).
>>>>
>>>>What's the difference,
>>>
>>>You should know.
>>
>> I do. There is none.
>
> So you don't.
>
> Of course you are free to consider that "relative velocity" =
> "closing velocity", you are so building a theory which is not
> consistent with experiment, that's all. Not a big crime, you're
> not a scientist.
>
> What you aren't free to do (because of logic), is to pretend that
> SR is contradictory because AE paper use alternatively c and c+v
> as light speeds. It is a relative velocity in the first case and
> closing velocity in the second one. SR does *not* assume relative
> and closing velocity to be the same.

I'm still waiting for you to say what the difference is.
You've been babbling on about vectors, why can't you
apply them?
Answer: because you are confused.
Einstein has confused you.

Androcles


.

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