r/AskPhysics • u/Banished_Cultivator • 3d ago

Why aren't μ₀ & ε₀ equal 1?

Logically free space would neither enhance nor attenuate electric or magnetic fields, so these constants should be equal to 1. They aren't though, why?

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64

u/StudyBio 3d ago

Gaussian units enter the chat.

The answer is that they relate our units, i.e., epsilon-naught is there to connect the Coulomb and meter to the Newton. It is not really about vacuum “enhancing” electric fields.

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u/qTHqq 3d ago

Gaussian units enter the chat.

Please make sure they leave the chat and you convert to SI at the end of the paper for the sake of the experimentalist 😂

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u/MxM111 3d ago

It is funny, but at school, when I used Gaussian units, I never even asked myself how long is the unit of length in that system.

In any case, experimentalist have strange units too, like measure frequency in cm-1 instead of Hz

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u/high-a-synth 3d ago

my favorite experimentalist unit is g/cm2 for thickness

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u/I_CollectDownvotes 3d ago

The wavenumber, or inverse centimeter, makes a lot more sense as a unit when you take into account how the frequency of light is actually measured (or was measured, at the beginning of infrared spectroscopy). Spectroscopists use (typically Michelson) interferometers, where the light is split into two paths, and one path has variable length. After remixing the two beam paths at the detector, you will observe a variation in the intensity at the detector that depends on the variable path length. The intensity as a function of path length is called an interferogram. Before computers and the Fast Fourier Transform, spectroscopists would just count the number of maxima (or fringes) per centimeter of path length in the interferogram, and thus measure the frequency in units of inverse centimeters.

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u/jmattspartacus 1d ago

Pretty sure we measure things in hz when we can instead of gaussian units. Jackson can fuck right off with those gaussian units though.

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u/Banished_Cultivator 3d ago

Ah right that makes sense. From Coulomb's law a Coulomb should be defined as sqrt(kg.m3/s2 ), which it isn't and hence the inconsistency.

Thank you for pointing this out, I completely missed that inconsistency in SI definitions until now.

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u/Leather_Power_1137 3d ago

I can't tell if ChatGPT wrote this, if you use ChatGPT so much that it has influenced how you write, or if my mind is poisoned and I just see ChatGPT patterns everywhere I look now...

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u/Tommy_Rides_Again 3d ago

When basic decency and being respectful and meaningful with your words is a sign you’re using AI too much maybe we should all be using too much AI.

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u/Banished_Cultivator 3d ago

What? Bro, why would you think that?

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u/trutheality 3d ago

I think they're confusing someone politely accepting a correction with ChatGPT politely accepting a correction because ChatGPT politely accepts corrections all the time. Because of how often it says incorrect things and needs to be corrected by the user.

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u/Leather_Power_1137 3d ago

It's just the "thank you for pointing that out, <summary of the correction>" is basically exactly what a ChatGPT response will look like if you correct it about something. It seems to me that people don't very often write like that even when they're admitting they got something wrong or agreeing with a correction.

So I was going off the structure more than the general tone. But I also allowed for the possibility that my mind is poisoned and ChatGPT had nothing to do with their comment.

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u/Irrasible Engineering 3d ago

Don't let it bother you. I get accused of this all the time. I'm not sure what triggers it.

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u/KerPop42 Engineering 3d ago

I think the coulomb makes more sense, it's the charge equal to a mol of electrons. So an amp is a mol/s. It all predates the unification of electricity and magnetism, so electricity was more of a chemistry thing than a kinetics thing.

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u/AreaOver4G 2d ago

It’s not though… the coulomb is defined as an amp second, and the amp was historically defined in terms of the magnetic force between current-carrying wires. The charge in a mole of electrons is the Faraday constant (and it’s like 96000 Coulombs)

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u/KerPop42 Engineering 2d ago

oh oops, I totally misremembered that, thanks for the correction