the definite or undefinite idea? - Page 1
Forum section: electronics / general

author: peterthenovice
author_rank: Regular Contributor
timestamp: April 21, 2013, 02:30:13 am
content: I have had some thought on what is measurement. How do we know for sure that 10.00000000mhz is 10.00000000mhz. How can we calculate the true precise value. how can we measure volts if there is no definite measure to calibrate from? everything changes throughout out time, so how is anything definite? how is a cubed micrometer measured in a definite way? My concision is that we can not perceive anything in a definite way. Is your black my black?Is my red your red?

author: vk6zgo
author_rank: Super Contributor
timestamp: April 21, 2013, 03:13:46 am
content: I think we are all good on total black,but all the colours you see are subject to individual variation.Our standards ultimately are built on faith.For instance,a unit of mass can be compared to other sub-units using a balance scale,but we do know that materials corrode over time,so does our unit of mass get more "massive" with corrosion,or less?If we take the velocity of light as a constant,then we have a building block to build all our other standards from.But first we must have faith in the constant we have chosen.It seems that faith is hardwired into humans------hence religion?We have done remarkably well over the centuries with the standards we have chosen,as we have found that they repeatedlywork out as if they are facts,so statistically,the possibility of error in standards is lower than your chances of winning Lotto.

author: c4757p
author_rank: Super Contributor
timestamp: April 21, 2013, 03:24:40 am
content: Quote from: peterthenovice on April 21, 2013, 02:30:13 amThese questions all have answers, just takes some research, and recognition of the fact that everything has an accuracy figure. There's no such thing as "1" volt (true mathematical number exactly equal to one) - saying so is a misunderstanding or oversimplification - but 1.00000 ± 0.001%? Sure. Do some research on metrology.QuoteCompletely different thing. I promise that your 1 is my 1, even if the display you see it on looks different to you.

author: ecat
author_rank: Frequent Contributor
timestamp: April 21, 2013, 04:11:12 am
content: Ignoring the very real possibility that you are on the road to insanityQuote from: peterthenovice on April 21, 2013, 02:30:13 amNo. At the very least, the background noise of neurons is almost certainly not identical.Quote from: peterthenovice on April 21, 2013, 02:30:13 amOnly on Tuesdays and even then only when it's raining.This is exactly why we need a way to measure, to pass an arbitrary or abstract value which can be understood and recreated by others. In order to have a measure we need a unit and for a unit to have universal meaning we require a reference.The reference can be just about anything, the length of a forearm or branch of a tree, the temperature at which water transforms from liquid to solid or gas, the time it takes for the sun or moon to make a repeat appearance in a certain part of the sky.If you and I were each to build a house with measure based in the length of our respective forearms the final results would differ in size but both would probably both make serviceable abodes. In this case we don't need absolutes, the relative ratios are sufficient as base variations are probably insufficient to cause problems.As our technology advances we discover that some properties once thought constant do vary under certain conditions, at this point we attempt to define our reference in terms of certain constraints or by finding some new more consistent reference. Additionally, the march of technology demands ever more precision, a second is but a heart beat and 400 years ago there was little need for any expression of smaller duration. Today I happily muse the milli, micro and nano while others consider pico, femto and atto, zepto, yocto and ultimately Planck time - the time required for light (in a vacuum I assume) to travel one Planck length(1), the briefest physically meaningful span of time.The briefest physically meaningful span of time. Sounds like we have time nailed, even if we struggle to define exactly what it is and even if events can occur within that span... Humm?So, physical constants measured ever more precisely with ever greater understanding of circumstances in which they vary until ultimately the granularity of the Universe intervenes and we are left with nothing but statistical probability of quantum chaos. Combinations of physical constants to express units and units to provide a meaningful, and mathematically manipulable, way to convey information. None of it is invented out of thin air and all of it is required for communication and understanding between us and our highly variable and impressionable senses and minds.(1) Planck length: defined from three fundamental physical constants: the speed of light in a vacuum, Planck's constant, and the gravitational constant. Theoretically the shortest measurable length due to uncertainty making the measure of any smaller length impossible.

author: EEVblog
author_rank: Unknown
timestamp: April 21, 2013, 05:40:54 am
content: Quote from: vk6zgo on April 21, 2013, 03:13:46 amNot quite, there are several fundamental constants that aredefinedas being the standard.There are 7 findemental constant from which all other are derived, including all our electrical ones.http://en.wikipedia.org/wiki/SIOnce youdefinesomething, then you only have to worry about how much the base SI unit will vary.For example, the inch wasredefinedto be precisely 25.4cm in the early-mid 20th century.QuoteIn the case of mass, there are four SI units which rely on it.This is awesome:

author: rsjsouza
author_rank: Super Contributor
timestamp: April 22, 2013, 01:09:39 am
content: Just a correction: 1 inch = 25,4mmAs Dave mentioned, the units are defined but in practice you will always have a certain degree of inaccuracy that depends on the precision of the equipment used to reproduce the standard in your lab...

author: Rufus
author_rank: Super Contributor
timestamp: April 22, 2013, 02:36:25 am
content: Quote from: peterthenovice on April 21, 2013, 02:30:13 amI hoped you would sober up and delete this but as others are commenting....The reality is we don't know any 'true precise' (whatever that means) value and we don't care.We have ways to measure things which have been amply demonstrated to provide consistent repeatable results within defined limits of accuracy. Maybe tomorrow they will stop doing that but until we observe that we will carry on assuming they won't.If two people measure something we can be confident they will come up with the same result, and more importantly if two people measure two things and get the same result we can be confident the two things are the same.If I measure a 3'x3' window frame I can be confident that buying a 3'x3' piece of glass (that someone else measured) will get me something that fits the frame. That is what is important The 'true precise' (whatever that means) of 3' is irrelevant.

author: peterthenovice
author_rank: Regular Contributor
timestamp: April 22, 2013, 02:44:20 am
content: I now see that there is a base of nature of a amp per Wikipedia. We have a base to the other electrical measurements.