Because scientists all over the world are working together, looking for answers to the same questions, just as much as if they all worked in the same physical laboratory in the same building. They need a way to share data and experimental results in a form that everyone can understand. ( D )
Let's say I perform an experiment and get very exciting results. I'm a good scientist, so the next thing I want to do is to publish a complete description of how I did my experiment, and include all of my results. That way, scientists around the world can read about what I did, they can find any mistakes that I made, and they can even repeat my experiment for themselves and see if they get the same results.
Now let's say that my results looked like this:
Result #1).
The reaction stabilized when it reached the rate of 1.26 briligs per tove.
Result #2).
After running at that constant rate for 35 toves, a pile of product was produced whose mass was exactly 61.284 wibbles.
Result #3).
When the pile of product was allowed to settle for another 20 toves, it had spread out, and covered an area of 14.907 square filks.
Do YOU understand my results ?
All those other scientists would have a tough time trying to decide whether my results made sense. And if they repeated my experiment, they would have no way to tell whether their results matched mine or not.
Without a standard system of measurement, and units that mean the same thing to everybody, us scientists literally could not communicate.
