# Units of Measurements in Space and on Celestial bodies?

Asked by interalex (130) November 22nd, 2010

Meter etc for distance, kilo etc for weight , liter for liquids, are all units of measurement on Earth
Must we use same or different measures and weights in space and on other celestial bodies when their size, orbit, rotation are different?
We understand that human beings on Earth can conceive reality with Earth’s existing systems.
All measurements are relative and not absolute.
They have to do with the cognition of the observer (human being?) on a celestial body or space.
1. Meter and metric system has to do with the 5+5 fingers (Arabic system) on Earth
2. Kilogram as above
3. Time is measurement of motion and relative to:
a. Day: Earth’s rotation creating the day (and night)
b. Month: Moon’s (Earth’s satellite) orbit around Earth creating the time of month (28 days, 7 days a week, used now as 30–31 days etc for known reasons).
c. Year: Earth’s orbit around the Sun creating/corresponding to the 365(¼) rotations (days)
d. Hour is connected to the rotation.
e. Light Year: As above depending on the Earth’s orbit.

Cannot we create universal time in a different way and not with reference to Earth?.
I mean that the reality is different in the Universe (As my father used to say 55 years ago)

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Rarebear (23434)

I love Science but only a Scientist could give you a correct answer.

philosopher (9143)

I thought that was the whole idea of the theory of special relativity.

josie (26284)

Sure we could do it. We need to have something that is a standard for anywhere in the universe. Here’s one suggestion.
Helium is stable and is found everywhere. Not as common as hydrogen but it is stable. We can base all distances on the diameter of the first orbital ring 1s2 on a Helium atom. Now we need to get mass. Let’s go with Helium again.
Time is another issue. Let’s pick a standard that is fairly common and is reasonably easy to measure. Let’s define it as the time it takes light to travel the distance of the first orbital ring. We can pretty much derive everything else from this.
Now you want to mathematically represent numbers. I agree with you that 10 is rather arbitrary. Ten fingers, ten toes. I’d either go with binary an easier multiple be like Hexadecimal. The units would not be as handy to use and would certainly be rather unwieldy but once you get past having numbers like Hex^25 behind your dimensions it would work.

Don’t hold your breathe. No one will be switching soon.

By the way, the meter is no longer defined by the old old standard of 1/10,000,000 the distance from the pole to the equator.
It is (from Wiki)
1960 October 14 – The eleventh CGPM defines the metre to be equal to 1,650,763.73 wavelengths in vacuum of the radiation corresponding to the transition between the 2p10 and 5d5 quantum levels of the krypton-86 atom.
1983 October 21 – The seventeenth CGPM defines the metre as equal to the distance travelled by light in vacuum during a time interval of 1⁄299,792,458 of a second.

Look up the other units and you will see they are not as “earth oriented” as you might think.

LuckyGuy (33521)

There is no such thing as universal time.

Rarebear (23434)

@Rarebear. That is a sticky one. But we have to come up with a standard. What would you suggest? You are hereby given a clean pallet. Whoosh!

2002 – The International Committee for Weights and Measures (CIPM) considers the metre to be a unit of proper length and thus recommends this definition be restricted to “lengths ℓ which are sufficiently short for the effects predicted by general relativity to be negligible with respect to the uncertainties of realisation.”

A decay rate? Ooooh ! How about a fraction of the time indicated by the big bang to a time near the present?

LuckyGuy (33521)

The speed of light is constant in the universe (as far as we know). That’s distance/time. Presumably, atomic dimensions and masses are constant too. One could create some system, but that would take time and effort.

RocketGuy (8437)

@worriedguy Everything in the universe has its own personal time clock, and it’s relative to every other time clock. It’s dependant upon velocity, gravitational field, etc. For example, time is running slower here on the surface of Earth relative to interplanetary space. Time runs slower for an object that is moving relative to an object that is stationary.

Rarebear (23434)

@Rarebear is correct. In addition, even if time is running “at the same speed” for two objects, other things are possible. I.e. for person 1, X might happen before Y, but the opposite for person 2.

Relativity is fun!

roundsquare (5512)

@interalex Great question. It looks as if you have received a healthy collection of answers, so I popped in just in case none had been provided, but since the subject is already under debate, I will just say welcome to Fluther. It’s always noce to have another science buff among the Jellies here.

ETpro (34386)

You could use planck lengths and times. See Planck constant.

Qingu (21160)

@Qingu That brings up an interesting point. In the pressence of a very massive object, say just outside the event horizon of the massive black hole at the center of our Milky Way Galaxy, what varies in the joule seconds (J·s) result? It would seem that as time slows, Energy must increase accordingly so that the Planck constant, h remains a true constant.

ETpro (34386)

@ETpro, @Rarebear, The challenge is to find a usable unit for time that someone on another (or maybe every) planet can use. We can change the definition to the time it takes light to traverse the He 1s2 ring when the observer is moving such that relativistic effects can be ignored. Time varies and we can describe that variation with relativity. Today on our planet we use the arbitrary unit, “seconds”, to describe time in the nonrelativistic regime and modify it with the relativity, gravitational, etc. fudge factors. The challenge is to find a unit that is not quite so arbitrary.
I’m open to suggestions.
Come on! We have to pick something! The fate of the universe is in our hands! :-)

@Qingu I do like the Plank’s constant idea.

LuckyGuy (33521)

@worriedguy Well are we trying to find a unit of distance, a unit of weight, or a unit of time?

Rarebear (23434)

I have already suggested a unit of distance and mass based upon He. I’m looking for a unit of time. I suggested the time it takes light to traverse a known distance. But, we are all open to suggestions. That is the point of the thought experiment.

LuckyGuy (33521)

@worriedguy Sorry, I missed that. So I assume it’s a rest mass of He?
A unit of time? Again, I don’t think that’s possible based upon Relativity.

Rarebear (23434)

@Rarebear We have to take relativity out of the equation, define the time unit and then put the relativity effects back in. After that I think we’ve got it.

LuckyGuy (33521)

@worriedguy Well, then, you’re on your own. I don’t know how you can take Relativity out of it.

Rarebear (23434)

@Rarebear Are you sure? Just because people will disagree about how much time has passed doesn’t mean that they can’t have a common unit of measurement.

Then again, I’m having trouble because the only way I can think of measuring time is with some speed/rate. But a speed/rate needs time. Hard to do this without being circular.

roundsquare (5512)

@roundsquare Well, you could use the cesium atom definition. from Wikipedia
the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom

Rarebear (23434)

Measurement of time:
We can make up a unit for the time with a simple method, viz by using a very common solid element (e.g. gold symbol: Au, atomic number 79.):
Gold time from solid to liquid.
Steps:
Make a piece of it liquid by heating and keep it in liquid state.
Then we place again an equal piece of gold on this liquid gold (with stable heating degrees) and we see how long it takes to liquefy and we call it a unit of time. This unit can be universal (however we face the difficulty of its sections/divisions; decimal system etc)

interalex (130)

@Rarebear I guess my problem is that we don’t know that this always takes the same amount of time. We can define time so that it does, but then we may well divorce our definition of time from what we want it to mean intuitively. Maybe thats okay, maybe thats not, probably depends on the context.

@interalex Same with your system. In addition, temperature is defined by the speed of the molecules which already requires time.

For normal life, we don’t have to worry about defining time, but thats whats getting to me now…

roundsquare (5512)

@roundsquare How do you know that we don’t know that it takes the same amount of time? Is that true?

Rarebear (23434)

@Rarebear Quantum mechanics tells us that things happen by random process. It can’t always take the exact same amount of time. Unless I’m wrong about QM, which is possible.

roundsquare (5512)

@Rarebear I would say the Heisenberg Uncertainty Principle proves that it is not possible to know that. I believe it is true.

ETpro (34386)

@ETpro The HUP just states that you can’t know the position and momentum of a particle at the same time.

Rarebear (23434)

@Rarebear My assumption was that we would need just such a measurement. What we were actually measuring was so far up in the thread I may be totally off on that. The HUP makes it impossible for me to know if I am. :-)

ETpro (34386)

@ETpro The HUP might make it difficult to actually measure something, but not to define the measurement.

roundsquare (5512)

@roundsquare We;; what good is a definition of a measurement that cannot be actually measured. :-)

ETpro (34386)

or