Scientists Get Closer To Redefining the Length of a Second (npr.org) 100
Scientists are inching one step closer toward redefining the length of a second. NPR reports: Atomic clocks, which look like a jumble of lasers and wires, work by tapping into the natural oscillation of atoms, with each atom "ticking" at a different speed. The worldwide standard atomic clocks have for decades been based on cesium atoms -- which tick about 9 billion times per second. But newer atomic clocks based on other elements tick much faster -- meaning it's possible to divide a second into tinier and tinier slices. These newer atomic clocks are 100 times more accurate than the cesium clock. But it was important to compare them to each other -- to "make sure that a clock built here in Boulder is the same as a clock built in Paris, as in London, as in Tokyo," [Colin Kennedy, a physicist at the Boulder Atomic Clock Optical Network (BACON) Collaboration] says.
"Ultimately, the goal is to redefine the second in terms of a more accurate and precise standard, something that we can make more accurate and more precise measurements with," Kennedy says. As the scientists with BACON [...] wrote in the science journal Nature last week, they compared three next-generation atomic clocks that use different elements: aluminum, strontium and ytterbium. The scientists shot a laser beam through the air in efforts to connect their clocks, which are housed in two separate laboratories in Boulder, Colo. They also used an optical fiber cable. What resulted is a more accurate comparison of these types of atomic clocks than ever before. [N]etworks of clocks like this could also be used as super-sensitive sensors -- to possibly detect a passing wave of dark matter, and to test Einstein's theory of relativity.
"Ultimately, the goal is to redefine the second in terms of a more accurate and precise standard, something that we can make more accurate and more precise measurements with," Kennedy says. As the scientists with BACON [...] wrote in the science journal Nature last week, they compared three next-generation atomic clocks that use different elements: aluminum, strontium and ytterbium. The scientists shot a laser beam through the air in efforts to connect their clocks, which are housed in two separate laboratories in Boulder, Colo. They also used an optical fiber cable. What resulted is a more accurate comparison of these types of atomic clocks than ever before. [N]etworks of clocks like this could also be used as super-sensitive sensors -- to possibly detect a passing wave of dark matter, and to test Einstein's theory of relativity.
How ? (Score:2)
Re: How ? (Score:2)
Re: How ? (Score:1)
Wild guess: Interference.
In other words: With itself.
Re:How ? (Score:5, Informative)
By counting.
The atomic clock (really, an oscillator) works by a microwave emitter working at a certain frequency. That frequency is used to excite some atoms which if they are precisely the right frequency (remember, wavelength, frequency and energy are related), will cause electrons to jump from the ground energy state to an excited energy state.
The magic is that inside the oscillator, it's possible to measure how many atoms are excited versus how many aren't. The frequency of the microwave emitter is then tweaked up or down slowly and the excited atom ratio re-evaluated. This repeats until the microwave emitter is "locked in" and the peak number of excited atoms is detected. At which point the output frequency of the microwave emitter is tapped and used as a reference frequency.
The wavelength(frequency/energy) has to be tweaked so the most atoms will get excited, which requires an electron to jump from its ground energy state to an excited energy state. The energy has to be precise - too high a frequency (too much energy) and an electron cannot jump, too low, same thing. But just right, and the electron can make it to the next orbital shell.
(This is because the energy levels are discrete from quantum mechanics. The element you use ha to be specially chosen to have really discrete energy levels as this will give the greatest "snap" - metals and semiconductors aren't good because in bulk they have wide energy bands making it hard to tune it precisely).
Once you have the signal of known frequency, it's easy to divide it down from many GHz down to a much easier to use frequency.
Remember, oscillator theory is basically a signal generator and a filter, and a loop gain over unity where the phase shifts more than 180 degrees. The microwave emitter is the signal generator, the atoms the filter. You can have poor filters using a resistor and capacitor, you get much better frequency stability using a quartz crystal because it only lets through a small band of frequencies, and the atomic excitation lets through an even narrower band of frequencies. Basically, the Q of atoms is off the charts.
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You don't count 1 thing happening, you accumulate a number of these things happening. Kind of like charging a capacitor, after a while you can tell how much volt the circuit averages, but you're not adding up and counting individual peaks and valleys. Same with most atomic things, in quantum mechanics things happen randomly, you just average them out at various levels so you get a distribution of the most likely vs the least likely.
We have systems that can oscillate and time very fast, so fast we can actual
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I'm sure
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Nothing at high frequency needs to be divided. A lower frequency can be multiplied and then the lower frequency divided, or there is nothing to prevent a mixer from operating at a high frequency and doing the phase comparison with a subharmonic directly, although it is not normally thought of that way.
Re:How ? (Score:4, Interesting)
It's not that fast - cesium clocks only run at a tad under 9.2GHz. Well within the frequencies commonly used for microwave communication.
Re: How ? (Score:2, Informative)
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Hence why they use measurements that are as independent from our environment as possible to figure out what a second is and then calibrate the rest around that.
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I remember the utter confusion when I loaned a 100ft steel tape measure to a friend. (I'd pinched the tape from work.)
Re: How ? (Score:2)
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OK, I checked [wikipedia.org]. The second moved from the Earth's rotation to Earth's orbit around the Sun in 1956 (as Suez was building up) and from the Earth's orbit into the atom in 1967. The successive definitions might not be comfortable or "homey", but they're not intended to be.
Atomic clocks? (Score:5, Funny)
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FFS just use a spinny thing that moves at precisely 1RPM and divide by 60, you can even write numbers around the edge.
Re:Atomic clocks? (Score:5, Funny)
Damn I knew the USAmericans used strange units of measures, but this one takes the cake*.
* using the standard 1kg metric cake reference, obviously.
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"The cake is a lie."
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Inching closer? (Score:5, Funny)
They're scientists.
They're centimetering closer.
Re: Inching closer? (Score:1)
Footing closer would be more natural though. Or tiptoeing closer? Yes, that's much better.
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Wait a second, that's not right.
Re: Inching closer? (Score:2)
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they're [2.54 centimeters)ing closer you mean.
Sounds odd. (Score:2)
Quantum gas atomic clocks are considerably more precise than conventional atomic clocks. You'd have thought these would have been targeted.
If not as a direct source, at the very least as a wholly independent means of measuring seconds, since the number of ticks they measure in this new second must be the same (allowing for gravity differences) in these different locations and the same number of ticks per the second versus these conventional atomic clock seconds.
Re:Sounds odd. (Score:4, Informative)
Going from the Nature paper itself rather than the journalist version in NPR. The intention of the experiment appears to be measuring the accuracy of a network of high precision clock sources for the purpose of other experiments like precise gravity detectors. This is why the facilities were separated by several kilometers and experimented with both open air and fiber based connections. That probably also explains why 3 different base elements were used, they want to perform the synchronization with different clock types.
Hate to tell you... (Score:1)
But at that precision, the clocks in those places won't be the same. If only due to gravity variations along the planet's surface alone.
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But at that precision, the clocks in those places won't be the same. If only due to gravity variations along the planet's surface alone.
Tourbillions were created to offset the gravitational pull on conventional watch designs because of physical gears being used.
How exactly is gravity, a factor here?
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But at that precision, the clocks in those places won't be the same. If only due to gravity variations along the planet's surface alone.
Tourbillions were created to offset the gravitational pull on conventional watch designs because of physical gears being used.
How exactly is gravity, a factor here?
Look at any analogue clockface and you will realize that there is 30 degrees between each hour.
Seconds can be measured by swinging a pendulum at a 30 degree arc for a wavelength of 2 seconds or a frequency of 1 second. If it is any more or less than +/- 15 degrees the amplitude changes and it is no longer an accurate representation of a second. Perhaps the wavelength is why a second is called a "second" instead of a "first" - but that's me speculating about words, the numbers are far more interesting.
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which also is the radius and diameter of the sun in miles, respectively.
No, they're not. The distance is off by 4 orders of magnitude.
The first is when the structure is viewed from the corner the length of each of the two angle sides of triangle you are presented with is is 43200 feet for a total of 86400 feet with both sides combined.
The length of the sides of the Great Pyramid is about 755 ft [wikipedia.org], not 43200.
You're spouting Time Cube-level nonsense.
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The most accurate pendulum swings 43200 times for 86400 seconds in a day which also is the radius and diameter of the sun in miles, respectively.
No, they're not. The distance is off by 4 orders of magnitude.
No, I'm off by 1 order of magnitude, there is no need to exagerate.
From the third sentence on Wikipedia's page on The Sun [wikipedia.org]: Its diameter is about 1.39 million kilometres (864,000 miles). Thanks for pointing that out.
The first is when the structure is viewed from the corner the length of each of the two angle sides of triangle you are presented with is is 43200 feet for a total of 86400 feet with both sides combined.
The length of the sides of the Great Pyramid is about 755 ft [wikipedia.org], not 43200.
I said the the two angle sides of triangle and you are referring to one base length. If you check those numbers you would find that adding *both* base numbers presented to you (as I said viewed from the corner where you can see two bases) is 755 + 756 feet is 230+230 metres = 460 metres, whic
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I did parse the first sentence incorrectly, I misread it as "radius and distance" instead of "radius and diameter".
The radius of the Sun [nasa.gov] is 432380 miles. If we ignore the orders or magnitude that's close, but not a match.
"the length of each of the two angle sides of triangle you are presented with is is 43200 feet" is just plain incorrect. It's 755 ft per side.
Your point about Earth's rotational speed makes more sense now that you show your calculation, but the rotation speed at the equator is 463 m/s.
My po
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One of these days - after Egypt removes the death penalty for people like me from their statute book - I'm going to go to the Great Pyramid, raise a glass of beer to Imhotep, then measure the sides for myself. That'll give me 4 values, all different, and I can derail any pyramidologist for the rest of eternity. It'll save so much effort in the long run. And I quite like the idea of visiting
Re:Love to tell you... (Score:2)
One of these days - after Egypt removes the death penalty for people like me from their statute book - I'm going to go to the Great Pyramid, raise a glass of beer to Imhotep, then measure the sides for myself.
I'll save you the trouble. You will need the J.H Cole Study [ronaldbirdsall.com] which is more accurate and has been verified as opposed to the Howard Vice or the "corrected" measurements which cause information to be lost. And you would have to raise a glass to Isis, wife of Osiris, so it's probably not a good idea to piss her off.
and I can derail any pyramidologist for the rest of eternity.
Well they're concerned with the alignment to Orion, I'm more interested in the numbers I can see. It's not a full time job, I just use bc and bash to help me figure things out.
That'll give me 4 values, all different,
True, because they al
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By the way, I've no interest in Orion, except as an astrophotography target.
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All measurements have uncertainties associated with them.
They are certainly a lot smaller than anything you're going to achieve by going there and doing them yourself. You are not going to get any better than a government funded project to survey those structures. You are talking about less than a millimetre error, you are *literally* splitting hairs.
Are you suggesting that there is a government conspiracy to publish fake dimensions of the Great Pyramid?
No error bars on any of those numbers? That is, and I use this word carefully, incredible. Not believable.
Yet the numbers are there mocking your dogmatic skepticism, twice, so I don't care what you believe. Perh
Re:Love to tell you... (Score:2)
I did parse the first sentence incorrectly, I misread it as "radius and distance" instead of "radius and diameter".
Ok, please keep in mind that I was posting tired about stuff I looked into several years ago, I'm not perfect either. Have you verified my claims about the pendulum? A 1 meter piece of string and a suitable weight is enough to verify my claims.
The radius of the Sun [nasa.gov] is 432380 miles. If we ignore the orders or magnitude that's close, but not a match.
Please consider the following three contextual pieces of information. 1. Ancient Egyptians didn't have the same equipment that NASA does. 2. The size of the Sun *changes* over time. 3. Where is the surface of the sun vs the atmosphere of the sun begin and end.
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Thank you for elaborating as to all of the challenges we've incurred to justify a tourbillion to increase accuracy on physical movements.
NOW tell me exactly what all of that has to do with measuring time at the atomic level using incredible frequencies.
Even the "old-fashioned" cesium atom refresh rate of 9 billion ticks per second, isn't exactly challenged with gravitational pull.
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Thank you for elaborating as to all of the challenges we've incurred to justify a tourbillion to increase accuracy on physical movements.
You're welcome.
NOW tell me exactly what all of that has to do with measuring time at the atomic level using incredible frequencies.
As I said: this is different from what the OP is suggesting however you can try this experiment yourself . I don't have an atomic clock handy to try the experiment myself. A one metre piece of string and a rock might cost about 1 cent. An atomic clock costs?
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There was a commercial one a couple of decades back which was in the "Rolex" range of prices. Steep, but not "sell your house and second-favourite child" steep.
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> How exactly is gravity, a factor here?
Higher gravity slows down time. No, seriously. That's part of relativity. If you take two identical clocks and put one on the moon for a year, then bring it back, the one that was in the low-gravity environment will have gone forward more. (Though it will tick more slowly during the high G forces of the trip to get there).
In my mind, the analogy is people moving around in a tank of Jell-O and another group in an empty tank. Moving through Jell-O slows everything
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So it's not a problem, like your wording makes it sound, it's an intended feature.
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Hmmm, is that 15 I count [slashdot.org]? Well, better than some, I'll grant. But you've seen nothing sufficiently stimulating in the last 2.5 years? Or do you just want to put up with my badly-written ones?
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This came on the heels of another story with an actual clickbait/teaser summary. There have been several of those hitting the front page lately. The summaries required clicking the referenced article for the stunning conclusion instead of summarizing it. This struck a nerve only because it similarly requires reading TFA. I admit, a small technical misrepresentation of a science/technical detail isn't fairly compared to clickbait blatantly sh
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What is the beef with NPR? I thought it was one of the few advertising-free sources in the States, and therefore one of the few possible considerations for reading. Not that I actually have time to go across the ocean for news.
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They have a hard political bias and are not advertising free. They happened to be the news source on the other side of a recent clickbait summary.
Of course most of the US media has gone off the deep end lately.
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And "lately"?
The way it presents itself on this side of the Atlantic, the overwhelming majority of American media has been stark staring insane since ... as far back as I can remember. It explains a lot about the average American. Though when you get to know them, not all of the insanity is consequent on the media - some seems to be home-made. Hah - I remember one whole crew of Americans who refused to leave their hotel rooms on the way to or from work and missed all the fun of travelling abroad fo
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I wonder how practical it would be to make a bunch of these things, stick them in a rocket and launch them into a few very high orbits. Might get interesting data out.
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https://www.sciencemag.org/new... [sciencemag.org]
https://www.space.com/nasa-dee... [space.com]
At those altitudes their precision is sufficient to make effects of gravitational time dilation apparent. And we can go back even further to where GPS was first introduced. Without compensating for both effects that are described by Special and General Relativity's time dilation,
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That's one of the applications listed in the abstract. If we can have incredibly accurate clocks at different locations, we can measure differences in terrestrial gravity. This is potentially useful for a LIGO like experiment for density changes instead of gravitational waves.
It's now officially 1/5th the time.. (Score:1)
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Date women? I thought people on Slashdot only had virtual 2D waifus?
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physical constants (Score:3)
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It's easy to know if they're constants or not, just look up the source code.
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The "So What Factor" (Score:4, Interesting)
I went digging and found this article [gpsworld.com], which notes that current GPS technology, when used with a handheld device like a smartphone, can be accurate to approximately 5 metres. The article discusses ways to improve this.
Now, if the limiting factor on GPS accuracy was time measurement, then improving the accuracy of atomic clocks by a factor of 100x might in theory improve the accuracy / resolution of GPS down. Now, it likely isn't appropriate to suggest that the accuracy would improve from 5 metres to 5 centimetres, for a bunch of reasons, not least of which is our ability to put a GPS satellite in to an absolutely *perfect* geosynchronous orbit. For example, Wikipedia's article [wikipedia.org] notes that satellites we think of as being in immobile, geosynchronous positions may in fact still trace a path, often seen as a "figure of 8" from Earth, due to various orbital eccentricities. These variations would have to be factored in to GPS calculations as resolution increases, because the timing differences caused by the satellite moving become more relevant as resolution improves.
OK, but would a 5cm resolution be more useful than a 5m one? Well, if you're driving to an unfamiliar address, the answer is almost certainly in the negative. But if you're a farmer and you're using GPS to auto-navigate your tractors or other farm machinery when it is seeding or spraying crops, then that accuracy might be really valuable. (In fact, it's so valuable that sometimes farms use local or "wifi range" transmitters to bounce signals, using fixed locations like fence posts as reference points. So maybe hyper-accurate GPS, as a product of more accurate time measurement, might actually be worth having...
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> current GPS technology ... can be accurate to approximately 5 metres.
It is important to note [gps.gov] the difference between UAE (User Range Error) which is < 0.715m 95% of the time, and UA (User Accuracy) which is 5m under open sky but can have centimeter accuracy with dual-frequency receivers.
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There's no such thing. Well, not unless you're able to remove the Moon from the question. And Jupiter, Saturn and the other planets down to (however low a mass you want to go).
Then you'll need to stop Earth from having earthquakes, which change the shape and distribution of mass in the Earth. Better stop mass moving from, say, the Greenland ice sheet to the Atlantic.
Testing Einstein's theory of relativity (Score:2)
Hasn't relativity been tested enough already?
One thing for sure, with all this testing, physicists don't work in the software industry. In theory, software has to be tested completely, at multiple levels, but these practices are like dark matter, supposedly everywhere but no one has observed it.
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Hasn't relativity been tested enough already?
This phrase does not mean what you think it does. People aren’t making the same types of measurements as hundreds or millions of other scientists and think they are going to turn anything up, it’s effectively been proven within measurement accuracy for those already. They test using things like higher energy levels, or on shorter time scales where people haven’t tried testing the relevant physics model. We know that relativity breaks down, but are unsure exactly where the theory starts
Gravitational Time Dilation (Score:2)
I am not a physicist. Now time dilation occurs between objects at different heights due to the effects of gravity. I read somewhere that the effect has been experimentally measured for height differences on the order of 1m. At what point to we need to take that into account when defining the second (i.e. do we define it by an optical atomic clock at a specified acceleration-due-to-gravity). That's the sort of thing that goes through my head when I read about this. I'm sure the physicists have it worked out
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An atomic clock's definition of the second would be equally valid far out in empty space as it would be in close proximity to a black hole. that is the core concept of relativity: the laws of physics are true no matter what your reference frame. Within each clock's reference frame, using that clock to define the second would yield perfectly consistent results for any experiment where you needed to measure the passage
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Well, we don't have to prove that light is the same speed in every direction as in our reference frame and all other systems we've explored, it is the same. If the math works out the same, you can interpret it any way you want.
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Thanks for your post about reference frames.
Let's do a quick thought experiment.
Four friends agree to meet for dinner.
They all leave their house at the exact same time.
They all walk exactly 4 MPH.
Friend A arrives and waits 3 minutes before friend B arrives.
Friend C arrives 3 minutes after that.
Friend D four minutes later.
Knowing they all went the same speed, we know the restaurant is closest to friend A's house. Since friend B arrived next, they're house is the next-closest. It took friend D a long time t
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You are correct; I mis-stated: GPS is more about triangulating distances from you to the satellites. However, the calculated distance to each satellite relies on the broadcast timestamps from each satellite; which are all in different reference frames (moving at different velocities, different gravitation
c? (Score:2)
So light will travel faster than the speed of light?
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So light will travel faster than the speed of light?
Or fast will travel lighter than the light of speed.
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Logic parsing error.
Program terminated.
Another BAD summary (Score:2)
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OUTCOME?
A Slashdot summary is not supposed to be a teaser for the article but rather a condensed spoiler.
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A Slashdot summary is not supposed to be a teaser for the article but rather a condensed spoiler.
Welcome to the Internet. You must be new here.
It's called clickbait. It's a global scourge, but as long as advertising pays for things (another and much older global scourge), it's inevitable.
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The real question this brings up... (Score:2)
No! No! No! (Score:1)
Scientists are NOT inching closer, they are millimetering closer!
length? A nanometer perhaps? (Score:2)
Re: length? A nanometer perhaps? (Score:2)
Re: length? A nanometer perhaps? (Score:2)
Re: length? A nanometer perhaps? (Score:2)
Wait a minute... (Score:2)
Very funny, yet... (Score:1)
Yet, on a serious note, since our 'second' is based on fractions of the period it takes our planet to orbit the Sun
and spin on it's axis, is it not time (no pun intended) to discover a more universal time period?
Perhaps something based on the Planck length and the speed of light?
Let's base it on the time it takes a photon to travel 1 Plank length in a pure vacuum.
Then, of course, scale up from there.
Seems it might better serve the u