Re: This about Newton's First Law
- From: sal <pragmatist@xxxxxxxxxx>
- Date: Sat, 28 May 2005 22:08:36 -0400
On Sun, 29 May 2005 00:10:31 +0000, Bill Hobba wrote:
>
> "sal" <pragmatist@xxxxxxxxxx> wrote in message
> news:pan.2005.05.28.02.23.22.569115@xxxxxxxxxxxxx
>> On Fri, 27 May 2005 22:10:41 +0000, Bill Hobba wrote:
>>
>>
>> > "sal" <pragmatist@xxxxxxxxxx> wrote in message
>> > news:pan.2005.05.27.19.04.42.402285@xxxxxxxxxxxxx
>> >> On Fri, 27 May 2005 02:56:40 +0000, Bill Hobba wrote:
>> >>
>> >>
>> >> > <geraldkelleher@xxxxxxxxxxx> wrote in message
>> >> > news:1117129736.977597.202340@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>> >> >
>> >> > Mr Savain has rightly pointed out that nothing moves in the early
> 20th
>> >> > century relativistic concept but the same applies to Newtonian
>> > terrestial
>> >> > ballistics applied to planetary motion.
>> >> >
>> >> > Bill
>> >> > It might be a good idea for you to explain what you mean by nothing
>> > moves.
>> >>
>> >> I can't comment on Savain's notion of reality,
>> >
>> > He is simply an idiot who can not even understand what a grade 8
>> > science student can - namely Newton's first law of motion.
>>
>> Yeah, well, perhaps I should have said I can't comment beyond that
>> observation which you just made.
>
> Ok. Form your own opinion - do not take my word for it.
Hey, I already did. Didn't take reading more'n a couple of his posts.
>> >> but the observation that
>> >> "nothing moves" in relativity is actually pretty reasonable, I think
>> >> ... at least from one point of view.
>> >>
>> >> In the 4-d representation of the universe, all events just "are".
>> >> They have particular coordinates which don't change. Worldlines are
>> >> sets of events, and they don't change either. In this sense, I
>> >> think it's fair to say "nothing moves", and thinking of it that way
>> >> can actually help with understanding it, IMHO.
>> >
>> > Errrrrr - Sal what would that make the v in the lorentz
>> > transformations then?
>>
>> The "v" in the Lorentz transformation is the 3-velocity -- or, rather,
>> the 3-speed, since it's a scalar, not a vector.
>
> It is a vector. The denominator contains v^2 which is a scalar but the
> numerator is a different matter. Of course in standard configuration it
> is a speed - which is what you may be considering. But in general it is
> not the case.
Come to think of it, yes, I was thinking of the standard configuration.
Sigh -- been away from this stuff since last fall, and the rust builds up
fast. Taking a little while to knock it off again.
[ ... ]
>> > In SR time is not
>> > absolute which is logically equivalent (via the POR) to locality and
>> > conversely in Newtonian mechanics time is absolute which is logically
>> > equivalent to no limiting velocity (ie no locality ie event A can
>> > cause event B instantaneously).
>>
>> Say what? Can you prove that any model which allows universal clock
>> synchronization must also allow unlimited velocity? I rather doubt it!
>
> Yes it can be proved.
Ah, right, so it can, if you assume the POR.
>> Newtonian mechanics certainly includes both,
>>
>>
> Come agian - Nwetonian mechanics assumes the Galelain trasformatons.
Right. It includes universal time and no limiting velocity.
>> and relativity includes
>> neither. By itself that's no proof that the two are equivalent.
>
> I have no idea what you mean by the above. To me, on the face of it, it
> does not make sense. Could you elaborate?
Relativity includes neither "no limiting velocity" nor universal time.
And yes I used a double negative there which sure didn't make it clearer,
did it?
>> > And that is the only difference. Both Relativistic mechanics and
>> > Newtonian mechanics still have the POR and the PLA - the difference
>> > is in the coordinate transformations.
>>
>> Um, right. But that's a big difference -- in particular, Newtonian
>> mechanics doesn't normally use any transforms of the form
>>
>> (x1,y1,z1,t1) --> (x2,y2,z2,t2)
>>
>> save with the time mapping t1 = t2.
>
> I beg to differ. See a full development such as Landau - Mechanics
> where the Galilean transformations are a central postulate.
Differ how? The Galilean transformation is a linear transformation on the
spatial coordinates, where that part of the transform includes a time
term, and a straight t1 == t2 mapping on the time coordinate. I'm lazy;
I'll quote from math world. In standard configuration it's (and I hope my
posting software doesn't mutilate this):
|t'| | 1 0 0 0 | |t|
|x'| = | -v 1 0 0 | * |x|
|y'| | 0 0 1 0 | |y|
|z'| | 0 0 0 1 | |z|
No matter how you rotate the spacial coordinates you always get t' = t,
which is what makes the 3+1 view so natural in Newtonian mechanics.
That's all I was trying to say, really. Is this at odds with Landau's
development? (I haven't got Landau here, sad to say.)
[ ... ]
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