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Greatest Equations Ever

sgant writes "What is your favorite equation? This was the question asked by Physics World in a recent poll. This is also covered in a New York Times article about the same poll. Some of the equations mentioned were the simplistic 1+1=2 and Euler's equation, ei + 1 = 0. What are some of your favorite equations?"

35 of 1,017 comments (clear)

  1. Re:Well... by Anonymous Coward · · Score: 5, Informative

    thats buttsex for those of you who dont know how to write an integral

  2. dupe of old poll by Gathers · · Score: 5, Informative

    "What is your favorite equation? ..."
    Shashdot has already covered this in a poll! We all already know that E=mc^2 is the overall favorite, closely followed by F=ma.
    http://slashdot.org/pollBooth.pl?qid=804

  3. Einstein's FULL equation by physicsphairy · · Score: 3, Informative
    The equation everyone knows offhand is E=mc^2 (even if they don't know what it means), but few people know that the full equations is E=m^2c^4 + p^2c^2. 'p' is momentum, so when you're talking about just the rest mass of the particle you have E=mc^2.

    Anyway, just thought I'd share that because E=m^2c^4 + p^2c^2 is my favorite equation and most people think it looks a little familiar but wouldn't know what it was without a little additional explanation.

    1. Re:Einstein's FULL equation by dasnake · · Score: 5, Informative

      I think your favorite equation should be E^2=m^2c^4+p^2c^2.
      Nah?

    2. Re:Einstein's FULL equation by ggeens · · Score: 4, Informative

      It's actually E^2 = (m^2 * c^4) + (p^2 * c^2)

      More like: E^2 = (m0^2 * c^4) + (p^2 * c^2)

      m0 is defined as the mass at rest (v = 0). If you substitute m = m0 / sqrt(1 - v^2/c^2), you can rework that to E = mc^2. And, if v = 0, you get E0 = m0c^2, the "energy at rest" of an object.

      I agree with the original poster, the full version is much more useful than the E = mc^2 form. The short form hides one of the most important conclusions of relativity theory: that mass is a function of speed.

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    3. Re:Einstein's FULL equation by physicsphairy · · Score: 2, Informative
      *sheepish grin* That's the second time I've done that now.

      I sure hope my calculations aren't where all that inexplicable "dark matter energy" has been coming from. . .

    4. Re:Einstein's FULL equation by Anonymous Coward · · Score: 1, Informative

      I agree with the original poster, the full version is much more useful than the E = mc^2 form. The short form hides one of the most important conclusions of relativity theory: that mass is a function of speed.

      Actually that's not actually what's in there. There's no such a thing as 'mass at rest'... At rest with respect to whose frame of reference???

      A more proper terminology and interpretation is that there's a thing we call mass which is the proper mass of an object, or the mass we measure on the frame of reference of the object itself.

      The equation, then, tell us that the relation between the energy of a body of mass m and it's momentum is not linear, as thought in Newtonian physics, but it's actually a quadratic wrt the speed of light. WRT a certain frame of reference moving at constant speed from our object, the amount of energy we need to increase its momentum by 1 (units of momentum, Kg*ms^-1 on the IS) is bigger the bigger the object's momentum is.

      The mass of an object is a constat, like the speed of light is. Talking of 'rest mass' and all that was caused by eager physicists trying to prove Newton's equations were still valid... But they are not, and telling ourselves lies won't help us understand the Universe better.

      BTW, E=mc^2 is the energy of a body of mass m on its own frame of reference; for particles that cannot have a frame reference, like photons and other particles that move at the speed of light, the relation becomes easier, as the massive term dissapears (cannot be mass as there's no proper frame of reference to define it in the first place!) E=pc (which is used a great deal in 1st quantification theories, and helps to find out through DeVroglie's relation the value of Plank's constant h).

      So E=pc is as important or even more than E=mc^2...

      BTW, the "right" way to write this is, being the tetra-momentum P^mu = (-cm, p), where mu=0,1,2,3; p is a three-dimensiona vector defined as gamma*mv (where gamma is the 1/sqrt(1-v^2/c^2) factor of Lorentz' transformations); ^ means superscript and _ subscript, and the metric tensor M^(mu nu) chosen so that the diagonal elements are time-space= (-1,1,1,1); we get that:

      E^2/c^2 = P^mu*M_mu^nu*P_mu = c^2m^2 + p^2

      which is the right formula for this case... QED

      and if we make c=1 as usual, we get that E^2 = m^2 + p^2; with frontier cases of E=m and E=p, which is easier to read and don't hide the physical meaning of the result...

  4. Re:correction by Ford+Prefect · · Score: 5, Informative

    It combines the 5 most important numbers in all of mathematics into a single formula.

    It's also got the other important mathematical concepts - exponentiation (i.e. raising something to the power of something else), multiplication, addition and equals. Essentially, it's a huge nugget of maths in a tidy little wrapper.

    I've got an old Sharp graphics calculator, which has both proper notation layout and a complex numbers mode. I still like keying in the 'e^(pi*i)+1', pressing 'Enter', then getting the zero, all perfectly laid out on a little LCD display...

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  5. Re:correction by Anonymous Coward · · Score: 5, Informative

    There's a difference between "Euler's formula" and "Euler's Formula", depending on whether you're referring to one of his formulae or the specific formula called "Euler's Formula".

    Guy created so many darn formulae that "Euler's formula" is ambiguous.

  6. Re:Submitter and Parent are stupid by pD-brane · · Score: 3, Informative

    No, everybody is correct.

    The only thing is that schematix (grandparent) misread the Pi as a 'n', which look very similar, indeed (on my screen anyway).

  7. Use the (HTML) source, Luke! by eric.t.f.bat · · Score: 2, Informative

    It's OK to use HTML on a website, you know. I suggest:

    <i>e<sup>i&pi;</sup> - 1 = 0</i>

    ... which will work nicely in most browsers.

    --
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  8. Mine, mine ! by sla291 · · Score: 2, Informative

    my stupid one would be : lim( sqrt(8) , 8->9) = 3 :)

  9. Re:Actually... by beaverfever · · Score: 2, Informative

    it wasn't for this equation, your cell phone wouldn't work.

    If it wasn't for the laws of nature things wouldn't work. The mathematical formulas are our way of expressing them.


    Mathematical formulas indicate an understanding of such laws, so without that understanding, your cell phone wouldn't work.

  10. Re:Take a guess.... by Gil-galad55 · · Score: 2, Informative
    Your system is axiomatic. If you assume that you have numbers that add and subtract as above, then of course they will! These are the axioms you have chosen for your system.

    If, on the other hand, you choose "simpler" axioms, then you might have to work very hard to get to the point of saying 1 + 1 = 2. Peano's axioms lead very quickly to this--in fact, they are about the same as the ones you stated. But you can assume any set of axioms you want. Much of mathematics is devoted to finding a "minimum set" of axioms for a particular branch, although as Godel showed, mathematics cannot be consistently axiomatic. Alas.

    --

    To follow knowledge like a sinking star, / Beyond the utmost bound of human thought. ("Ulysses", Tennyson)

  11. Re:correction by sgant · · Score: 4, Informative

    It was my mistake in the original posting. Not the article from Physics world, as I couldn't put in special characters.

    Talk about throwing the baby out with the bathwater!

    --

    "Leo Fender was in a 'state of grace' when he designed the Stratocaster." -- Paul Reed Smith
  12. Re:V=IR by Technician · · Score: 3, Informative

    Obviously another person who never uses AC.


    What's wrong with AC. R is resistance, not impedance or reactance. If you add reactance to the equasion, then you need a new formula, but that equasion has current, voltage and resistance. The formula holds true. Don't read in inductance and capacatance where there isn't any.

    This is Ohm's law, not Kirkoff's law.

    For formulas that include reactive components, they are listed here;

    http://www.tpub.com/neets/book2/6.htm

    --
    The truth shall set you free!
  13. and driving the joke into the ground we get .. by Suchetha · · Score: 2, Informative

    you've made an error in your initial assumption, which gives a wrong answer

    First we state that women require time and money:
    Women = Time X Money
    error--^
    this should be
    Women = Time + Money

    and from there onwards ..

    And as we all know "time is money"

    Time = Money

    Therefore by substituting Money for Time we get:

    Women = Money + Money

    Women = 2(Money)

    And because "money is the root of all evil" we therefore can state:

    Money = (Evil)^1/2

    And Since

    2(Money) = Women

    and

    (Money)^1/2 = Evil

    And we are forced to conclude by substituting "women" for "(money)2" from above that:

    Women = 2((Evil)^1/2)

    or in words
    women are double the root of all evil

    which means absolutely nothing

    but hey when you're a maths nazi..

    Suchetha

    --

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    or one out of three ain't bad
  14. Re:V=IR by AuMatar · · Score: 3, Informative

    You're making a big mistake- you're assuming R has to be a constant. It doesn't need to be. R is the resistance, which can be a formula. Actually, it is a formula- R=l*psi/A where l is length, A is cross sectional area, and psi is the resistivity of the substance (which again, can be a formula that takes in temperature, or may be a constant for given material and temperature).

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  15. Re:Take a guess.... by Anonymous Coward · · Score: 1, Informative

    To be precise, which is always a virtue in issues of math: It's at proposition 110.643 on page 83 of the second volume of Principia.

  16. Schrödinger! by k98sven · · Score: 3, Informative

    Come on, folks? The Schrödinger equation!

    H*Psi = E*Psi
    (note: H is an operator folks, not a number)

    Perhaps not as famous as E=mc^2.. or as exact as the Dirac equation (relativistic version of the S.E.),
    but.. in terms of practical benefit to mankind, I think this one has done more than any other equation during the last century.

    Atoms. Molecules. Semiconductors. Lasers.

    The number of things explained and modelled by the Schrödinger equation are just uncountable. You can explain almost* all of chemistry with that thing.

    Relativity is nice, but it hasn't had the technical uses quantum physics has.

    (*Relativistic effects are important in heavy elements. For instance the yellow color of gold is a relativistic effect.)

  17. The axioms of set theory by ortholattice · · Score: 4, Informative

    The answer is simple. The most beautiful equations, hands down, are those from which all of mathematics can be derived. These are the axioms of ZFC set theory. What could possibly be more beautiful or more important than that? And it's a shame so few people know about them. See Zermelo-Fraenkel Axioms and Metamath Proof Explorer.

  18. Re:V=IR by klaasvakie · · Score: 2, Informative

    Obviously another person who never uses AC

    At any moment in time the equation V=IR holds for any circuit (yes, even AC circuits). It is just that when you have caps and inductors in your AC circuit their impedance changes all the time, making the V=IR equation less usefull.
    When one only has resistive impedance elements it is possible to use V=IR for AC circuits by replacing V with Vrms, and I with Irms, the Root-Mean-Square value of the AC voltage or current, giving Vrms = Irms*R.

    --
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  19. Re:ThinkGeek t-shirt by tootlemonde · · Score: 2, Informative

    "2+2=5 for extremely large values of 2" is sometimes called "Fermat's next-to-last theorem" and is said to be the occasion for a duel with sabers between Tycho Brahe and Manderup Parsbjerg in 1566.

    You can read about the grisly outcome here as part of the discussion "Did Tycho Brahe really have a silver nose?".

  20. Re:correction by saider · · Score: 2, Informative


    What is important is the key fact in its proof, which is that for any value 't', e^it = sin(t) + i*cos(t)


    If you have taken calc 1, this should be readable. Think of it this way.

    e^it, shows up a lot in engineering formulas, but can be a pain to work with. Being able to convert it to a sin/cosine formula makes it simpler because for certian values of t, sin() or cos() will be 1 or 0, and derivatives and integrals are fairly simple (eg. sin(x) d/dx = cos(x) ).

    --


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  21. Slightly old news... by wongn · · Score: 2, Informative

    This news story was in The Times about a month ago... I can recall it interviweing some of the people that voted for 1 + 1 = 2 as the best equation. Euler's was probably the best of them. In itself it seems to show the beauty and... strangeness of math in that three entirely irrational numbers that you'd feel have no link whatsoever can be so intristically linked.

  22. Re:correction by Enigma_Man · · Score: 3, Informative

    that is Pi up there, not n. It's a very small font, so it may look like an n, but it's actually a PI symbol...

    -Jesse

    --
    Nothing says "unprofessional job" like wrinkles in your duct tape.
  23. Re:correction by TildeMan · · Score: 3, Informative

    Actually, it's not named after Euler, just by him. He did pick the name for the constant, but only picked 'e' because a, b, c, and d were already common elsewhere.

  24. Re:Actually... by Mikkeles · · Score: 4, Informative
    'As far as the laws of mathematics refer to reality, they are not certain; and as far as they are certain, they do not refer to reality.'

    - Albert Einstein, Sidelights on Relativity

    --
    Great minds think alike; fools seldom differ.
  25. Re:correction by SamSim · · Score: 2, Informative

    That would be the Euler-Lagrange equation.

  26. Re:correction by ralphclark · · Score: 2, Informative
    Actually,
    F+V = E+2
    is generally known as Euler's relation, probably to distinguish it from Euler's equation.
  27. Re:Impressions of math equitations. by mark-t · · Score: 2, Informative
    For any number base n, there are n distinct symbols that can be used to represent the magnitude of that value. Any representation of a number with more than n distinct symbols in it cannot possibly be taken as a number in base n.

    In layman's terms, in base 1, 1+1=11, 11+1=111, 111+1=1111, and so on. This is consistent with the requirement that the number of symbols in a number represented in base n contains no more than n distinct symbols. But base 1 contains mathematical inconsistencies when representing non integers (or even the integer 0) which can't permit it to be acceptable as a valid base.

  28. Umm, electricity has negative. by Anonymous Coward · · Score: 1, Informative

    Negative numbers exist in nature, in electricity.

  29. Re:correction by shoor · · Score: 2, Informative

    Actually, according to the wikipedia, Euler was not the first person to discover this, but rather, Roger Cotes. Though the wikipedia says he proved it in an obscured form. Search for "Euler's formula" in the wikipedia to confirm.

    --
    In theory, theory and practice are the same; in practice they're different. (Yogi Berra & A. Einstein)
  30. Wow: Try this in Google! by rpcxdr · · Score: 2, Informative

    Who needs a calculator anymore? Google cannot be stopped:

    e^(pi*i)+1

    1. Re:Wow: Try this in Google! by Pharmboy · · Score: 2, Informative

      actually, been using the calculator available in my.yahoo.com for many years now. and its a bit more intuitive.

      --
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