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Hallo Currere,
yes, you´re right. But. If they visit us and we have real contact then there´s no problem. You only have to take a watch from us and a watch from our visitors - you´ll see both time-codes. Then you know f.e. how long 1 kfeheurftgh in Earth seconds is . When we have real contact we could clear all language/physics-problems, but if you only have radio-contact how you want to tell them, that you want to know their time or else. I think, there´s no need to think about specified problems, if we/they don´t understand a simple "Hello". And this is only the 2nd problem. The first problem is, that we don´t have the same technics. Can you watch a terrestrial TV-programm on your computer when you don´t have a TV-card inside? We´ll never find a way to translate their radio-contacts because we don´t know the decoding process. All what we would have were an oscillationwave or a Bit-text.

Ciao René

rmendler schrieb:

You are making a broad range of assumptions. For someone that can travel between the stars, why would they wear a watch? If they can reach us, we are the primitive ones.

Those that developed the metric measurement system 2 centuries ago attempted to satisfy both commerical and scientific uses. The major SI units are no different than those proposed 200 years ago, this before the scientific community even identified atoms.

James Clerk Maxwell objected to the meter being identified as a scientific unit of length. Our measurement system is "provincial" and archaic. It is perfectly suitable for commerical use, but it fails to meet the needs of the scientific community, otherwise they wouldn't keep trying to create what they call "natural" systems of units.

Try Euclidean Natural Units as an option, they are mathematically defined using the relationships of a simple Eluclidean shape.

In my opinion there are some faults in this discussion.

currere schrieb:

That is wrong.
en.wikipedia.org  (english)

de.wikipedia.org  (german)

Some units are defined by using atomic dimensions which they did not use "200 years" before.
e.g.

currere schrieb:

Sorry, but rmendler explained it correctly, the "number" is completely unneccessary. U can easily transfer "m" into a different system which uses the average distance of the protons in H2 at a specific temperature. So the numeric value differs, but u can calculate with the factor and then communication about length is possible.
Same for time, (see definition above). And the speed of light in a vaccum is a natural constant, like pi is one. So our length and time is allready based on what u try to search for. They try to make a definition for mass based on natural constants, but to count a certain amount of atoms is not yet possible (or to define it by the avogadro-constant, 22,4 liters which a normal gas at normal conditions ).

currere schrieb:

Yes, that is why u could define time by it
so
time = (frequency) x (number of osszilations of a certain element, e.g. H2)
And the frequenzy of a molekul can be measured in whatever system u imagine.

time = frequenzy x (number of osszilations, e.g. H2)

Example:
1s = 123456 (osz per second) * 8560 oszilations (numbers not correct!!!)

transfering 10 seconds into alien time (alien time unit is "thomas" ):
...

Thomas Mc Kie schrieb:

Two hundred years ago the French created and adopted the metric system.

lamar.colostate.edu 

Thomas Mc Kie schrieb:

The current SI second is based upon the duration of the average Ephemeris second, then they determined how many cycle counts of the cesium transition fit within that duration. The Ephemeris second varies, thus they decided to use a stable reference. It is still based upon an astronomically defined unit of time.

www.sizes.com 

The meter is a clock-dependent definition for length, plus how do you measure the speed of light without having pre-defined what unit of length it travels in one second. I like the Swiss definitions better than those at NIST.

www.metas.ch 

Thomas Mc Kie schrieb:

The speed of light is not equivalent to a mathematical constant. The speed of light (SOL) measured in a vacuum is a conditional value, as the SOL varies with the permittivity of the medium in which is can transverse. The permittivity of "free space", whereever that is, has not been measured. We know the numeric value of permittivity in a vacuum on the earths surface, at least to the limited precision of the SI units.

The scientific community needs a "reference" value and the current value for the SOL is just that, a reference. The earth second has no mathematical relationship to the physical sciences except by definition. The Euclidean "second", which I call Tau, is mathematically defined based upon a physical science constant.

currere schrieb:

Yes, but which part of the system is the same like it was when it was created?
Would u agree that:"Over hundret years ago the Germans invented the car, and nowadays cars are no diffrent to these 100 years ago."?

That is what u said with "The major SI units are no different than those proposed 200 years ago"

I do NOT understand the problem, even if they would define it by the average time light needs from earth to the moon and this time period would be called 1 moons, we would have a clear definition. The matter of fact is, that in a definition u need to define a reference. It is impossible to have a "universal" reference. If u want u could measure the length of saying "Hello, my name is" in seconds. Then declare that "Hello, my name is" as 1 sentenceunit and from then on u measure with that.
That the second wasn't that exact in former times is not the problem, because as u defin 1 second today as a certain periodlength it is from then on much more precise. U do not have to correct the second before that new definition. Maybe I don't get the point, maybe u do not understand waht I try to tell u.

Same for this, I don't understand the problem. There is not any existing constant which is measured without any error. Physics try to make this error as little as possible, but even in ur pi there is an error, because it is measured.

If u combine two measured constants to define another unit, the error propagation is calculated. U will learn a lot about measuring and errors when u have physics at university.

To ur mathematical constant:
It has also a unit, but on earth we normally know it and so it is not mentiont after the numeric value.
But the number "4" could be "100", it could also be "aa" (a=1, b=2, c=3; basis 3^2,3^1,3^0).
I can construct u millions of systems to express the number 4 (decimal system). That is why u still have to tell ur comunication partner how u define ur system. Else it would be impossible for him, to understand u.

Now I consider we get a transmition of another species. How could we "read" what they wanna tell us.

1) The other species does not try to communication with unknow species, they try to comunicate with a spaceship from their planet and we "accidently" get this message.
---> If we are very very lucky, we could have the right idea how they are sending their information, but with the utmost probability we will never understand what they sent.

2) The other civilisation tries to communicate with unknown species (us). For sure they will not try to make it more difficult than absolute neccessary for us to decode their message. In order to establish a contact they will probably use a binary code. Maybe within this code, there is other information implemented (like in "Contact"). But again, it will not be crypted if they want a contact.
The only possibility that it'll be crypted I can think of is, that they only want to have contact to a civilisation of a certain knowledge level. But again, the "hello, we are here" message will not be crypted anyway, because this would lower the chance to establish a contact even with a intelligent civilisation way too much!

Greets

Thomas Mc Kie

Thomas Mc Kie schrieb:

I think it is possible to have a "universal" reference. There were quite a few people that thought that SI would never be adopted because of its choice of units. The scientific community needs to look beyond satisfying both the "commercial" and scientific requirements in every unit.

We already have mathematical constants that have no error. It is when we attempt to relate them to some "physical" phenomena there is a precision problem.

You are intermixing the term "measure" wiith calculate, as we calculate Pi rather than measure it. I have not heard that numbers like Pi and the square root of 2 being in error because they are transcendental. Their precision is limited only by our computational capability.

Accumulative measurement error is a different issue than computational limits.

Euclidean Natural Units provide a one to one numeric relationship with frequency and the velocity of light.

vip.ocsnet.net 

The numeric value for the velocity of light is the same numeric value for the frequency of the hyperfine emission of neutral hydrogen. For equation (4), if you use a cosecant value corresponding to the angle of 26.25400 degrees, the resulting frequency is 1420.405 MHz, as Tau is equal to the duration of the second at that angle. In Euclidean units the velocity of light would have that same numeric value, differing only in unit designators. However, the SI definition for the speed of light uses an "unnatural" unit of length.

Hallo Currere, hallo Thomas,
the main problem, we have, is still, that we don´t have anything to translate their messages. We need something like "the stone of Rosetta". Real communication only is possible when we have a physical contact. Because we could talk with "hands and feet" to learn the languages from each other.

@currere: why do you think that super-technology-races need no time instrument? Here on Earth the intelligentest scientists also need a watch, because they have to know, when it´s time for lunch - the wife is waiting!!!! I think if someone does space-voyages the time is much more necessary as in a low-level-culture.

Ciao René

currere schrieb:

Hm, physical constants are only limited by measuring systems...
Could u explain me the square root of 2 by using "universal understandable" words?
I agree that the square root of two is exact like 1/3 is exact too. But without explaining what "/" is this is useless. Communication about maths has to start with the natural numbers, because it is easy to understand.
Try to decrypt this signal (n=peek, _ no peek)

n_nn_nnn_nnnnn_nnnnnnn_nnnnnnnnnnn_.....
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
n_ _ _n_ _nn
nn_ _ _n_ _nnn
n _ _ _nn _ _nnn
nn _ _ _nn _ _nnnn
nnnnn _ _ _ _ n _ _ nnnn
nnnn _ _ _ _ _ _ nn_ _nn
nnnn _ _ _ _ _nn_ _nnnnnnnn

If u understand what I transmitted now try the same for pi or squareroot of 2.