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Topic: Physics from logic?(Check my math)
Replies: 135   Last Post: Jun 7, 2012 1:25 PM

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 namducnguyen Posts: 2,334 Registered: 12/13/04
Re: Physics from logic?(Check my math)
Posted: Apr 14, 2012 2:04 PM

On 12/04/2012 3:30 PM, Rotwang wrote:
> On 12/04/2012 04:46, Nam Nguyen wrote:
>> On 11/04/2012 9:49 AM, Rotwang wrote:
>>> On 11/04/2012 03:57, Nam Nguyen wrote:
>>>> On 10/04/2012 8:51 AM, Rotwang wrote:
>>>>> On 10/04/2012 15:11, Nam Nguyen wrote:
>>>>>> [...]
>>>>>>
>>>>>> Btw, " by definition"? I thought physics quantities are _measured_ ?

>>>>>
>>>>> Not in this case, no. The metre is defined to be 1/299792458 times the
>>>>> distance travelled by light in a vacuum in 1 second.

>>>>
>>>> Same question, really: why would light not travel at 99.9999999% of the
>>>> current constant speed, instead of 100%?

>>>
>>> Because that doesn't mean anything.

>>
>> It means you were incorrect in interpreting my question. Speed of light
>> is _a ratio_ which happens to be a constant of the value 299792458,
>> based on the standard of unit of length and time. And it is a
>> _measured_ unit: _no one defined that value_ !

>
> Wrong. Look, you've already written ITT that your knowledge of physics
> is virtually nil. Mine is not.

"virtually nil" doesn't mean "literally nothing", the last time I
checked English.

> your purpose to learn the answers or do you just want to defend your
> misconceptions indefinitely, like usual? Because if it's the latter then
> I'm happy to leave you to it, but if it's the former then please read on.

That's just idiotic babbling, a la Inquisition style. You were incorrect
in denying the constant _speed_ of light is a physics _measured_
quantity.

Taking your opponent's non-technical a-manner-of-speaking "virtually
nil" _to force_ an acceptance of your argument, and then threatening
to quit the argument if your opponent doesn't accept what you said
is a non-starter. In any rate, what you said about the speed of light
not being a measured physics quantity is dead wrong, which I'll will
assert and explain again (as I've already explained), whether or not
you leave the conversation.

>> Your answer above is incorrect because a) it's circular: "times the
>> distance traveled by light in a vacuum in 1 second" already connotes
>> the speed of light already whose constant value is at the heart of
>> my question (why not other constant value?);

>
> This question is like asking why the ratio between a metre and an inch
> is not some other constant value. The ratio is not measured, it is
> /chosen/ by defining one unit in terms of the other.

So, you said: "The ratio is not measured".

> There is no reason
> why it is what it is, rather than some other constant value, other than
> convention. It will never be determined to be anything other than what
> it is by experiment;

Tell us, Rotwang, in _physics experiments_ if physicists didn't
_measure_ anything, would they just "meditate" on the constant speed
of light and come up with the common agreement that the value be
299792458?

Shouldn't we call that Zen, instead of Physics? Or are you saying the
two aren't distinguishable?

> the only way its value will change is if we adopt a
> different definition of the metre or the inch.

What kind of physics here did you claim you knew?

How does what you've just said above invalidate my question
as to why the constant isn't 99.9999999% of what it is?

(Read: you'd get a new constant value but the 99.9999999%
question remains the same question.)

>
> Do you wonder why the ratio between a metre and an inch is not
> 99.9999999% of what it is, instead of 100%?

Not that one in particular. But suppose I had, I'd have had a
correct answer for it. Would you have an answer for it in this
case?

Read: Do you know what is meant by the phrase _NON-LOGICAL_ in
mathematical reasoning context? (As in "non-logical axioms".
Note the relevance of the thread's title:

"Physics from logic?(Check my math)"!

>>> The main lesson of Special
>>> Relativity is that there's no absolute distinction between space and
>>> time, much like there's no absolute distinction between length and width
>>> - length and width are mixed into one another by rotations, while
>>> distance and time are mixed into one another by boosts.

>>
>> That's vague

>
> I made it vague for the sake of brevity. Here's the non-vague version:

But how would all what you said below solve the question why the
constant speed of light is at its current value, whatever the unit
you choose?

> According to SR (which is a good approximation whenever gravity is close
> to uniform), the laws of physics are invariant under an action of the
> PoincarĂ© group, which is the group of isometries of Minkowski space. The
> PoincarĂ© group includes, among other things, rotations about the z axis,
> which look like this:
>
> x' = x*cos(theta) - y*sin(theta)
> y' = x*sin(theta) + y*cos(theta)
> z' = z
> t' = t
>
> and boosts along the x axis, which look like this:
>
> x' = (x - vt)/sqrt(1 - v^2/c^2)
> y' = y
> z' = z
> y' = (t - vx/c^2)/sqrt(1 - v^2/c^2).
>
> These show that there is no absolute distinction between width and
> length,

Sight. Where did I indicate I'd like to debate about the "distinction
between width and length"?

My question is really from what mathematical, logical reasons, the
constant value for the 'c' is at whatever the value it is, and not
something else?

Do you _really understand_ my question?

>> In any frame of reference traveling at a constant speed, the ratio
>> between the space length of (say) 1 trillion proton long _in a frame_
>> and the however many number oscillations, state transitions (of certain
>> atomic particles) during the traveling of light over this distance
>> _in the same frame_ is a constant that would be measured in all such
>> frames.

>
> It is a constant (as far as anyone knows, and pretending that "1
> trillion proton long" makes sense), yes, but that isn't the same thing
> as the speed of light in a vacuum -

Your reasoning is incoherent here. In this context, we always by default
assume we're talking about the speed of light in vacuum. So your "It is
a constant" and that isn't the same thing as the speed of light in a
vacuum" don't rhythm together.

> this much is apparent from the fact
> that, if the above-defined constant were to change, the speed of light
> in a vacuum would still be exactly 299792458m/s by definition of the
> metre.

> Instead, measuring a different value for the constant would mean
> that at least one of the length of 1 trillion protons or the duration of
> an oscillation or state transition of the certain atomic particle had
> changed (if the oscillation happens to be that of the radiation
> corresponding to the transition between the two hyperfine levels of the
> ground state of the caesium 133 atom then we can rule out the latter, by
> definition of the second).

Do you know that your last paragraph above has proved that the
definition of a "metre" here is just a red herring and that you
were wrong in claiming the speed of light were a defined and not
measure physics quantity.

First, length and time are defined by purely _physical entities_
NOT by convention: how many proton-long, how many oscillation-duration.

Secondly, all physics quantities _MUST BE MEASURED_ . The reasoning
being is in SR (at least) we can't talk about, say, motion without
frames of reference (and let's recall that light is never motionless).

A train is moving from where I stand; and you on the train.

The _very same train n-proton long at rest_ and the very same light-
photon (or light wave-front), passing over the train from end to end.

The problem is since I'm not on the train I can only use my measurements
on the ground to measure the length of the train which _to me_ would
appear to be n1-proton long, where n1 < n (SR length contraction).
And the time it takes the very same light wavefront to pass the train
from end to end would be m1, where m1 < m (where m would be measured
when the train is at rest to me; this is SR time dilation).

But to you though, being on the moving train relative to me, the train
is still n-proton long and it'd take the same light wave front
m-oscillation duration to pass the train end-to-end.

It also happens that _my measured_ ratio n1/m1 and _your measured_
ratio n/m turn out to be identical value (no matter how fast or slow
the speed of the train be).

If there were no measurement involved, you could in effect just
take the ration n1/m to be the speed of light, which is wrong
(and which would be variant). So I hope you understand now that
as far as _frame of reference_ is a _required_ notion in SR, then
_ALL physics quantities are MEASURED_ !

My original question is then why that constant value (in all frames of
reference) is _that_ particular value, instead of something else
a little less, or more. And this has nothing to do with the definition
of "metre", which, as I've shown above in the ratios n1/m1, n/m, is
irrelevant and expendable!

I have an answer to the question: there's just no logical and
mathematical explanation: it's just a permutation in the realm
of physical existences.

--
----------------------------------------------------
There is no remainder in the mathematics of infinity.

NYOGEN SENZAKI
----------------------------------------------------

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