I Replacing the Measurement standards (SI units)

[N1206]

The wavelength of the cosmic background radiation is now ~2 mm (millimeters)
It started at ~500 nm (nanometers) when the universe first became transparent.
Something you measured as 1 m long at the beginning to the universe is now ~4000 m long.
We, at the end of things, measure something by bouncing photons off it and interpreting their return.
The Uncertainty Principle shows that we can either pin down an object's position with great precision, or pin down its energy, but in either case our precision hits a boundary that we can never exceed, so how long something is can never be exactly measured.
So too, the units that we define cannot be used beyond a certain level of precision.
And then there is relativity. An observer traveling as significant fractions of c will not perceive events in the universe the same as an observer at rest...and neither of them are wrong. An item you perceive as being a meter long or an event being a second in duration depends upon your velocity in relation to the item or event.

You may think that it is semantics, that the unit has remained constant and that the object or event has changed, but it is not semantics. A unit system is peculiar to the time and place of its users and its usefulness to them in agreeing upon what they perceive. When they are NOT in the same time and place, adjustments become necessary.

https://physicscentral.com/explore/...elativity by,functions within about 2 minutes.

I don't know how the GPS units make their adjustments--by shaving off a number of clock ticks, or by saying that each clock tick actually measured more time (stretching the unit) But given that the ticks are what is counted, I reckon they have actually adjusted the units.

 

[olgerm]

The wavelength of the cosmic background radiation is now ~2 mm (millimeters)
It started at ~500 nm (nanometers) when the universe first became transparent.
Something you measured as 1 m long at the beginning to the universe is now ~4000 m long.

A unit system is peculiar to the time and place of its users and its usefulness to them in agreeing upon what they perceive. When they are NOT in the same time and place, adjustments become necessary.

So you think that length of meter is now 4000 times smaller than it was then? So for example distance between hydrogen atoms in hydrogen molecule ($H_2$), which is now $7.4*10^{-11}*m$, was then $1.85*10^{-14}*m$?
What do you think is exact function to calculate length of meter at any time? Do you think it is inversely proportional to wavelength of the cosmic background radiation $l_{meter}(t)=(l_{meter}(t_0))^2/l_{wavelength\ of\ the\ cosmic\ background\ radiation}(t)$?

The Uncertainty Principle shows that we can either pin down an object's position with great precision, or pin down its energy, but in either case our precision hits a boundary that we can never exceed, so how long something is can never be exactly measured.

How does that make you think, that SI-unitsystem units are different in different places and times?

 

[N1206]

You seem to be missing my point.
Consider an observer directly underneath a geostationary satellite on the equator.
Both measure the length of one day, from noon to noon, in seconds with identical atomic clocks.
Their measurements will not concur.
Consider a being who created 'le grand metre' out of iridium at the beginning of the universe, entered stasis, and measured his 'le grand metre' now. The measurements will not concur.
So what good was the precisely defined unit, then?

You can define a set of units to be static, but the universe you use them on is not static.
Something winds up getting adjusted.

 

[gmax137]

Consider a being who created 'le grand metre' out of iridium at the beginning of the universe, entered stasis, and measured his 'le grand metre' now. The measurements will not concur.

Is that true?

And, How do you propose the being "measure" the iridium rod now?

 

[Mike S.]

The most welcome of the SI unit changes is already underway, but stealthily. You may not know it, the physicists here might even disagree with me, but the ampere is already among the walking dead - a nonstandard unit for 1/96485.3 mol charge/second. (Mol charge can be written as "Eq" if you like). All the electrical units can be replaced this way. Eventually you'll be flipping a 0.2 mmol/s circuit breaker! Couldn't happen too soon. :)

 

[Ibix]

Is that true?

Yes, because metal evaporates over time so the bar will erode over such timescales, even neglecting that the early universe was a very hot place and iridium wouldn't be solid at an early enough time. Not because of the expansion of the universe, though.

 

[Nugatory]

The Uncertainty Principle shows that we can either pin down an object's position with great precision, or pin down its energy, but in either case our precision hits a boundary that we can never exceed

You’ll hear that a lot, but it is not correct. The uncertainty principle places no limit on how precisely a quantity can be measured; you get as many decimal places of precision as your measuring instruments are good for. It is true that…

how long something is can never be exactly measured.

but that is not because of the uncertainty principle. It’s because no matter how good our instruments are, there’s always room for further mechanical improvement.

So too, the units that we define cannot be used beyond a certain level of precision.

That was the case with the traditional definitions based on reference objects, but not with the new SI definitions. The modern definition of the meter, for example, specifies a length that can in principle be measured to arbitrarily great precision so can never be obsoleted by improvements in our measuring instruments. The better our instruments, the more exact our meters.
This is quite unlike a standard based on some reference artifact; for example a reference meter bar can never be more exact than the inevitable fluctuations in its length as atoms on the surface go walkabout. Were our measurement technology to improve enough to detect these fluctuations we would find ourself unable to say what a meter “really” is, just that it’s somewhere between the extremes of the fluctuations.

 

[olgerm]

You seem to be missing my point.
Consider an observer directly underneath a geostationary satellite on the equator.
Both measure the length of one day, from noon to noon, in seconds with identical atomic clocks.
Their measurements will not concur.

It is not because length of units is different in different places or times, but because length of time between same events may be different in different frames of reference.

Consider a being who created 'le grand metre' out of iridium at the beginning of the universe, entered stasis, and measured his 'le grand metre' now. The measurements will not concur.
So what good was the precisely defined unit, then?

Yes, because metal evaporates over time so the bar will erode over such timescales, even neglecting that the early universe was a very hot place and iridium wouldn't be solid at an early enough time. Not because of the expansion of the universe, though.

Meter is not defined by prototype metre bar (etalon) anymore. Even if length of some metal bar changes, length of meter would not change.

 

[olgerm]

I add measurement uncertinity to my post 13.
with probability 68% the units are in following range:

$4.790 482*10^{-43}*s >t_b>4.790 589*10^{-43}*s$
$1.4361 502*10^{-34}*m >l_b>1.4361 825*10^{-34}*m$
$1.5389 542*10^{-8 }*kg>m_b>1.5389 888*10^{-8}*kg$
$1.326211322 086*10^{-18}*C >q_b>1.326211322 296*10^{-18}*C$
$1.0018 068*10^{ 32}*K >T_b>1.0018 293*10^{32}*K$

backward conversion to SI units:

$2.0874 259e*10^{42}*t_b>s>2.0874 728*10^{42}*t_b$
$6.96 290*10^{33}*l_b>m>6.96 306*10^{33}*l_b$
$6 497 9192.16916563*m_b>kg>6497 7731.82586359*m_b$
$7.5402764 503*10^{17}*q_b>C>7.5402764 490*10^{17}*q_b$
$9.981 965*10^{-33}*T_b>K>9.981 740*10^{-33}*T_b$

for example charge of electron in these units is $q_{electron}=0.12080854741532157(91054)*q_b$

Instead of using "multiplied units" that I described in post 13 it would also be reasonable to just define all physical quantities are in these units (so length of an object means how many $l_b$s is the object long). and to just use real numbers as "units". To make these real numbers more easily memorable and calculateable these could be for example integer powers of 2. Specific powers can be chosen to be in right order of magnitude for specific application. for example to use $2^{140}$ as "unit" of time, $2^{112}$ as "unit" of distance, $2^{22}$ as "unit" of mass, $2^{40}$ as "unit" of electric charge, $2^{-104}$ as "unit" of temperature.


an example of using these units: we know:

distance from village A to village B is $4325*2^{112}$. [it is approximately 3.225*km]
average speed of a car is $13*2^{112}/2^{140}=13*2^{-28}$ [it is approximately 52.27*km/h]

we can calculate that the time it takes for car to drive from 1 village to another is $4325* 2^{112}/13* 2^{-28}=332.6923076923077*2^{140}$. [it is approximately 3.7023285266031474 minutes]


another example of using these units:we know:

we have an airballon that is charged with static electricity. Its electric charge is $q_1=0.2*2^{42}$. [it is approximately $1.1665478153119035*10^{-6}*C$]
we have an airballon that is charged with static electricity. Its electric charge is $q_2=0.1*2^{42}$. [it is approximately $5.832739076559517*10^{-7}*C$]
These balloons are distance $r=0.2 *2^{112}$ away from each other. [it is approximately 14.914*cm]

we can calculate that the repelling force between the 2 balloons is $q_1*q_2/r^2=0.2*2^{42}*0.1*2^{42}/(0.2 *2^{112})^2=0.2*0.1/0.2^2*2^{42+42-112-112}=0.5*2^{-140}=32*2^{-146}$. [it is approximately 3.4549187 newtons]



But 1 obvious advantage of SI is that it is hard to measure some things with small measurement uncertainity using these units. For example to accurately measure time between 2 events using SI units is possible by using atomic clock that uses caesium 133 atom. But using these units the measurement uncertainity would be bigger, because caesium 133 frequency itself has big uncertinity in these units. So it is harder to compare time intervals in different observations if these units are used instead of seconds.


In addition to units there could also be standard to define standard chirality.