A Confession from a former “keV” Junkie: 1. It’s a Plague.

(Inspired by vlk’s “keV vs keV”)

Beside the obvious benefit of confusing the public and colleagues in other fields, the apparent chaotic use of physical units like keV and Kevin has an addictive convenience beyond a simple matter of convention. Yes, I said “convenience”.

All roads to Rome, All quantities to Energy

In fact, mixing up the units of the physical quantities doesn’t end with energy and temperature.  If I am the one breaking this to you, then I am terribly sorry, but the plague has already spread to pretty much all the physical quantities.

Energy = Temperature = Mass = Length = Time = …

So, there you have it: Energy costs Money since Time is Money.

At the center of this pandemic, you find “energy”, which seems to be the culprit, linking all of them together. Although, once they are all linked, it doesn’t really matter. This appears a gross misuse or misunderstanding of these quantities at best. Now what drives “normal” physicists to become “keV” junkies if there is such a thing called normal physicist? Well, the answer is already in vlk’s slog about “keV vs keV”.

Ice, Water or Vapor

Do you know what it feels like at T=200 K, T=300 K or T=400 K?

Of course, it’s a matter of being frozen to death, being comfortable under the sun shine or being burnt to death.

Ok, then, now how about T=10,000 K, 10,000,000 K, or 10,000,000,000 K?

Hmm, hmm, interesting. Very hot, extremely hot, and hellish hot? I know I will be dead either way.

A shear number of zeros is already annoying and begging for another unit or a shorter form, but more importantly, it seems that we, … I mean, normal human beings don’t really have a good “physical” feel of Kelvin, Celsius or Fahrenheit at these high temperatures. Why should we? After all, we use Celsius or Fahrenheit for the daily use, and it’s not like that we need to burn and destroy T1000 to save the humanity everyday. Even so a couple of 1000 K heat might do the job.

Ok, ok, Let me think for a moment for change.  Judging from a factor of 1000 differences which is a lot more than 100, there’s got to be equally significant differences in the matter at these temperatures. Perhaps changing-their-physical-state kind of differences?

Hmm, only if we have an easy way to express the state change or a unit to convey the essence of their differences. A-ha, yes, yes, I knew it’s not our fault, our ignorance or lack of our knowledge.  It’s the useless unit here that keeps us in the dark. The unit is good at around, say, less than 1000 C.  Just like T=0 C means ice to water and T=100 C means water to vapor.  More than that, this K, C, or F is so useless.

De Nile isn’t just a river in Egypt, and it flows in our mind too, quite beautifully I suppose.

Wait a minute, there are more states than solid, liquid and gas?

  1. vlk:

    You make a good point, Jaesub. We do tend to use units where the physically interesting range seems to always go from around a few hundredths to a few hundreds. Anything beyond, and somebody invents a new measure. This is why interplanetary distances are listed in A.U., coronal heights in RStar, interstellar distances in pc, intergalactic distances in Mpc, and so on. The few apparent exceptions, like the H column density NH (which is usually around 1e20 cm^-2), upon further inspection turn out to be “correctly normalized” (because in this case absorption cross-section is around 1e-22 cm^2 and it is the product of the two that is the interesting quantity).

    09-10-2008, 8:01 am
  2. hlee:

    As long as these ambiguous/convenient units and their ambiguous/convenient transformations are shift invariant or scale invariant or both (WLOG), same statistics thrive. People still live after the tower of Babel. We need good translators, though.

    09-10-2008, 9:59 am
  3. vlk:

    They are not always scale or shift invariant (e.g., wavelength vs energy, flux vs magnitude, events vs binned counts, etc).

    btw, there seem to be some rather persistent comment problems. I keep getting error messages saying I am posting spam. The only way to get rid of it seems to be to first write the comment, copy the text of the comment (ctrl/cmd-C), reload the page, paste the text (ctrl/cmd-V), and then hit submit.

    09-11-2008, 10:40 am
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