Talk:Planck units/Archive 2

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This is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.

1 In case you haven't noticed...
2 NPOV violation
3 Proposed change
4 Dimensionless measurements
5 Dimensionless measurements 2
6 Dimensionless measurements 3
7 Dimensionless measurements 4
8 Planck area?
9 A question
10 ET and Planck units
11 2006 CODATA values out now (at NIST site)

In case you haven't noticed...

Natural units no longer redirect to Planck units. i tried to get sections set out for all of the different proposed systems. I am using K.A. Tomilin: NATURAL SYSTEMS OF UNITS; To the Centenary Anniversary of the Planck System as a source as well as Michael Duff: Comment on time-variation of fundamental constants as sources in addition to including Atomic units and Geometrized units. Unlike the Duff paper, i do not want to assume at the outset that the Coulomb Force Constant is unity $\frac{1}{4 \pi \epsilon_0} = 1$ and i want to use symbols already in use here in WP rather than the symbols that Tomilin uses. Tomilin gave me permission, via email, to borrow liberally from his text and i plan to. i think the Stoney Units deserve their own article but i don't have the spit for it. r b-j 06:50, 30 July 2006 (UTC)

NPOV violation

Normalizing the coulomb force constant instead of, say, the elementary charge or permittivity of free space and to consequently make the relevant Planck units depend on this without majority academic support is a personal choice and thus a violation of NPOV. -- Dissident (Talk) 18:02, 3 August 2006 (UTC)

the reference cited is clearly made. historical qualification is clearly made (Planck did not define a natural unit of charge). Planck units, as they are presently used, do not normalize the elementary charge. there are plenty of other systems of natural units that normalize elementary charge. it may not be your POV, but it is the common use in the phyics community. don't believe me? take it up in sci.physics.research or check with some of the leading physicists that are wikipedians (like User:John Baez). the coulomb force constant is normalized in Planck units just as it is commonly in the cgs electrostatic units. (and probably for the same reason, which is why most hard-core academic physicists say that the fine-structure constant is $\alpha = \frac{e^2}{\hbar c}$ instead of $\alpha = \frac{e^2}{\hbar c 4 \pi \epsilon_0}$ .)

personally, i wish that it was ε₀ that was normalized (as also 4πG instead of just G) so that flux and field strength was the same thing and so that Gauss's law is simplified. but that's not what they did. just because they made a sytlistic mistake in convention (in my POV) doesn't mean that i, or anyone else, gets to change the meanings of the definitions that are presently the common use. r b-j 18:32, 3 August 2006 (UTC)

Proposed change

"In fact, we have no understanding of the Big Bang before the age and size of the universe exceeded one Planck unit, and its temperature fell below one Planck unit"

Is this a better way to put that sentence? I was confused with the present tense for a while. Past tense seems better.

Alternately, "in fact, we presently have no understanding of the Big Bang before the age and size of the universe exceeded one Planck unit, and its temperature fell below one Planck unit" ... leaves the possibility open for future understanding of the Big Bang processes.

Elronxenu 11:32, 15 August 2006 (UTC)

hey, the Bogdanov brothers have already figured it out (what happened before the Big Bang, and, presumably during the Planck era). i might recommend instead: "in fact, we presently have no understanding of the Big Bang before the age and size of the universe exceeded approximately one Planck time and Planck length (respectively), and its temperature fell below approximately one Planck temperature" (the "approximately" because of the ambiguity of including some 4π or 8π factors in there or not, a possible oversight by Planck and even current physicists.) r b-j 18:52, 15 August 2006 (UTC)

Sounds good, I added the main part of that change but left out the clarification of "approximately" because I am not a cosmologist. Elronxenu 13:12, 2 September 2006 (UTC)

Dimensionless measurements

The Invariant Scaling article still bothers me. It still looks like a rough draft in which the argument is not concisely expressed. Also it still looks too partisan. For example, it defines measurement as a dimensionless ratio. I agree that measurement can have this aspect - e.g. any given length divided by a unit of length is necessarily a dimensionless ratio. However, a given length can also be interpreted as multiples of a unit length, and this is not even a ratio let alone a dimensionless ratio. The article's emphatic insistence on the former definition is a bit tendentious, I think, since it seems to justify Okun's rather extreme views (extreme even by the standards of his colleagues, if you read the cited texts). If all measurement are simply dimensionless ratios then obviously Okun is right and there are no dimensionful physical constants. Yet even Okun's colleagues argue for some dimensionful physical constants. In other words, I think the invariant scaling article doesn't need Okun and would be better off without its implicit endorsement of his views. I think this endorsement is an accidental by-product of the drafting process and that the drafting process should therefore continue. Lucretius 23:26, 27 September 2006 (UTC)

hi Ross... long time.

first, i think you meant to Michael Duff instead of Lev Okun, no? if you do mean Duff, it's not really that he's saying there are no dimensionful physical constants, it's that he's saying that the value of those constants, as we or anyone else measures them, are really an expression of the units we use to measure them and not a consequence of a meaningful physical parameter ("no operational meaning" i think are Duff's words)

second, do you agree with this line from the nondimensionalization article? :

Measuring devices are practical examples of nondimensionalization occurring in everyday life. Measuring devices are calibrated relative to some known unit. Subsequent measurements are made relative to this standard. Then, the absolute value of the measurement is recovered by scaling with respect to the standard.

(i didn't write it, so i'm not appealing to my own authority.) did you notice that John Baez was here and stated last May that "I'm pretty happy with the page as it stands. " [1] and even yesterday did an (inconsequential) edit to the very section that did not touch any of the content you are bothered by? if there was something factually wrong with the content, i think that John would have changed it. he has done content edits to Physical constant where there is a similar kind of issue going on, this time with User:Kehrli.

please take a look at the n-Category Café

then, do you disagree with this statement?: "assuming we could communicate with the aliens on Zog qualitative fact and numerical information, there is no way that we could ask them to compare their measurement of c or G or h to what we measure to see if they are consistent. no way to do that at all. but it is possible to ask them to measure α and tell us if they get the same number that we get. likewise with m_p/m_e or any other ratio of like-dimensioned universal quantities." that one i'll admit is mine. if we tell the aliens the size of our meter stick in terms of the Planck length and the length of our second in terms of the Planck time, then when we ask them to measure the speed of light in vacuum, could it even be possible that they could reply with a different value than 299792458 m/s? now we could communicate to them the length of our meter and second in terms of another set of natural units, such as atomic units or Stoney units, and then the answer they give will have dependence on α, but that is because α is operationally meaningful. it is conceivable that they could respond with a different numerical value for alpha.

lastly, what changes do you think should be made? r b-j 06:09, 28 September 2006 (UTC)

Hi RBJ.

Yes, there has been a mix up of names. By Okun I meant Duff. By Ross I think you mean me, Lucretius.

but i think your real name is Ross, no?

Anyhow, to the point:

Firstly, DUFF does take a radical view - in the cited text by the 3 authors, his contribution is titled 'A party political broadcast on behalf of the zero constants party'. The title is tongue-in-cheek but the content is seriously meant and he is talking about zero dimensionful constants, which is radical even by the standards of his 2 colleagues. His radical view follows naturally from a very exclusive definition of measurement as a dimensionless ratio, a view that the article endorses with such statements as 'The only quantities that we ultimately measure in physical experiments or in our perception of reality are dimensionless numbers'. This is an extreme statement and it implies that we ultimately live in a dimensionless universe of numbers. Duff's colleagues on the other hand believe there are some dimensionful constants, a view that follows naturally from a broader interpretation of measurement to include both dimensionless ratios and multiples of dimensionful units. Their view is plain common sense.

As for how I think the article should be written - I think you should aim for greater economy of expression. The introductory paragraph is long-winded and repetitive, as is the body of the text. The final paragraph is a conspicuous example of illucidity (I seem to remember that someone other than you wrote that one). I think the quote from Barrow is good but I don't think the article needs references to Duff et al, especially as there are other authors who express the case more simply and effectively. I would rewrite it myself but I have already made a firm commitment not to edit it again and I intend to stick by that.

Regarding the aliens from Zog, I wish them well. I'm sure if we could communicate with them in English or in Zoggian we could also manage to translate our units into theirs and vice versa without necessarily resorting to dimensionless ratios, assuming of course they do have units rather than just numbers at their command.

and this, my dear Lucretius is mistaken. we must have some common reference. perhaps it could be the Bohr radius, perhaps the reciprocal of the Rydberg constant (both are lengths), but in any case, those are candidates for a natural unit of length. same for time. nonetheless, if we communicate to them how long our meter stick is and how much time our second is, depending on the system of natural units we would have to use as a common reference, either they will have to measure the speed of light to be exactly 299792458 m/s as we do (that would happen if we defined the meter and second in terms of the Planck length and Planck time) or, if it came out differently, some dimensionless constant (most likely α) is different for them than for us. this is fundamental. the Zogians will measure the speed of light to be 1 Planck length per Planck time just as we do. to translate that to 299792458 m/s is just a matter of scaling. r b-j 23:05, 28 September 2006 (UTC)

Regarding Baez, I'm surprised to learn that he has been here but I am even more surprised that he should endorse the article. As far as I can recall, he aims for lucidity and simplicity in his own writing, a style that comes easily when you really know your stuff. Amateurs like you and me inevitably struggle to get our ideas across but I don't think we are struggling hard enough in the Invariant Scaling article. Maybe we don't know enough. If Baez made a small change to the article, maybe he was itching to make bigger changes.

i dunno, let's ask him. i imagine he's eventually watching this.

Anyhow, it's good to debate with you again and I'm glad you continue to patrol the Planck page. You're a bit like a trout patrolling a stream. I knew I'd get a bite if I dangled my line in it. Cheers. Lucretius 124.177.136.198 11:23, 28 September 2006 (UTC)

it depends on how much time i have at the particular moment. i might not have bitten for a few days.

anyway, i fully admit that the "paraphasing" or expansion or language of explanation in that section is mostly mine (but, being an encyclopedia, i thought elucidation is appropriate as long as non-factual stuff stays out), but the main concept, that it's only the dimensionless physical constants that are truly parameters of meaning defining the nature of the universe, is actually pretty uncontroversial in the physics community which is why Duff responded pretty harshly to the VSL claims made by Moffat, Davis, Davies, etc. it's a little like the current unverifiability of string theory, if the speed of light was different, how would an experiment measure or verify such a change? howver, we know how a difference in α would be noticed and if α changed sufficiently, we know life would be a helluva lot different. i realize that you think this is r b-j POV, but what i am really trying to do is to reflect the POV of the credentialed physics community (but with a paraphrase of mine that anyone else could have written). in a sense, it is virtually a tautology, i think it is nearly that uncontroversial. r b-j 14:00, 28 September 2006 (UTC)

Hello again, RBJ. I wish you wouldn't insert your replies into my text as this makes it difficult for me to get an overview of your argument. In fact I only discovered some of your replies by accident while reviewing one of my own arguments, and that was after I had already started my reply to your argument. Also your replies seem very hurried and that doesn't help with clarity. You should take more time to answer otherwise I won't get the benefit of your knowledge. Now for my reply to your interspersed replies:

I know you are trying to represent the POV of 'the credentialed physics community' but the particular slant that Duff has on that POV is hardly mainstream. I agree that 'only the dimensionless physical constants are truly parameters of meaning', but this POV does not require us to believe that all measurements are ultimately dimensionless ratios. The debate between Duff, Okun and Veneziano would be impossible if they all thought that measurements are ultimately dimensionless ratios - they are debating about the merits of different dimensionful constants. In fact their debate amounts to an argument about which dimensions have real physical significance and which are merely human constructs or abstractions. For example, we could argue that the dimension of force is a mere abstraction derived from the real dimensions of mass, space and time, and then we could argue that mass is an abstraction derived from energy, space and time. And so on, until we finally select the dimensions we think are physically real. That selection in turn decides our choice of dimensionful physical constants. But if all measurements are ultimately dimensionless ratios, then all our dimensions are ultimately abstractions and we live in a universe that is profoundly mysterious. There is some validity in such an argument but it has more to do with philosophy than science - Socrates and Duff might be comfortable with it but Okun and Newton would not, nor would the great majority of humankind.

If the article is to represent the POV of the scientific mainstream then it needs rewriting. In particular, you shouldn't overstate the dimensionless nature of measurements, particularly since this is not essential to the argument.

One more thing - how could the Zoggian fine structure constant be different to ours? Wouldn't that mean they live in a different universe, with atoms that function differently to ours? I think an interview with a Zoggian would go something like this:

"Greetings, Earthling!" "What the hell are you? And what do you want?" "I am from the planet Zogg and I want to learn how you measure things" "OK, this is a meter and that clock there tells the time in seconds. The speed of light is 3x10^8 meters per second." "Ah! Our unit of length is the Zogg, which is about half one of your meters. Our unit of time is the Ogg, which is a third of one of your seconds. The speed of light is 2x10^8 Zoggs per Ogg. But nowadays we include temperature in the measurement. The thermal speed of light in a vacuum is 8 500 Zoggs per Ogg Nord, or 1 Arbeejay. Arbeejays have real physical significance, but Zoggs, Oggs and Nords are mere abstractions. How do you measure temperature?" And so on. I'm not convinced that natural units like Plank units would be necessary for a meaningful exchange. In fact, how would you show a Planck length to a Zoggian unless he happened to be very tiny? Wouldn't you first have to use larger units of length such as the meter and then introduce him to the Planck length? But maybe you know more about this than I do. Lucretius 02:21, 29 September 2006 (UTC)

okay, L, this is a little humorous, but it misses the point. if the Zogs were to come here, we could show them a meter stick and have a common reference for length. but the axiom is taht the Zogs are "over there" and we are over here and all we can do is communicate qualitative notions and numerical information. so how do we communicate how long or big or massive or old something is (like a meter or a second)? if we use Planck units then we are already defining that their speed of light is meaningfully the same as ours. we cannot ask them to measure it in terms of these common units and expect an informative answer because they will, by definition, get the same value we do. so a varying c has no meaning. but this is not true about α. we could meaningfully inquire if it is the same for them as for us and if it is different, something is different for them. if α is significantly different, yes, atoms would no longer exist and neither would the Zogs. but if it is less (or slightly) different, we know that it's different and their existance is different. r b-j 03:17, 29 September 2006 (UTC)

sorry, but i'm interspersing comments. i'm pressed for time.

Thanks RBJ - your reply here is more carefully phrased than the other ones. But as far as I can tell you still haven't answered the question. Assuming you can only talk to the Zoggians by radio, how would you explain to them what values you assign to Planck units?

by use of the very expressions in the article, $l_P = \sqrt{\frac{\hbar G}{c^3}}$ , $m_P = \sqrt{\frac{\hbar c}{G}}$ , $t_P = \frac{l_P}{c} = \sqrt{\frac{\hbar G}{c^5}}$ , $q_P = \sqrt{\hbar c 4 \pi \epsilon_0}$ . if they're smart enough to communicate with us, they will already be thinking about the same universal units. there are issues of $4 \pi \$ that would have to be settled (i think that it should be $\epsilon_0 \$ and $4 \pi G \$ that is naturally normalized to one and i would bet the Zogs would too. but that's a different issue and, even with this difference, it puts us in the same ballpark.

Apparently you can't explain the Planck length in terms of the Bohr radius since their atoms might be different to ours.

no, you do it the other way around. that's how we ask them how life may be different for them than for us.

So what is the unit of length that would allow you to define Planck length accurately? You can't send them an equation for Planck length since it would include dimensionful quantities you haven't explained to them.

no, they have a concept of gravitation, of wave mechanics, of relativity and E&M. it's just that we cannot ask them to measure the speed of light using these common concepts and units of length, mass, time, and electric charge and expect a different answer than we have. even if, somehow conceptually $c \$ is different for them than for us, it makes no operational difference and there is no way that this could be communicated one way the other. but if $\alpha \$ is different for them than for us, that is operationally meanigful and that fact can be communicated.

It seems to me that the science of Zogg must be forever out of our reach until you can overcome this objection. Lucretius 07:05, 29 September 2006 (UTC)

i really don't know what you mean about that, but L, i am not sure you do either. r b-j 14:14, 29 September 2006 (UTC)

OK RBJ, this is disappointing. You are making some very big assumptions here. For instance, some of the equations you sent the Zoggians assume they know what you mean by the gravitational constant G. But you would first need to supply them with Planck values for them to work out the value of G. The fact is that you are inevitably caught in a circular argument. In order to communicate Planck quantities to the Zoggians, you must employ other quantities that they already understand. Atomic units would be ideal except you have already ruled those out on the grounds that their atoms might be different to ours. If their atoms are different then everything is different and we do not share any quantities that we can translate into Planck quantities.

Of course this whole aliens business is simply a recycling of an argument initiated by Planck himself. As far as I recall, he said "These are units even aliens would understand." If the aliens already understand these units, we can use them to explain our other units. But if the aliens don't yet understand Planck units, those units need to be translated via other units. In that case, what Planck should have said is this - "These are units that even aliens would understand, provided we first explained them in terms of other units that are common to them and us." Of course he didn't say this because it would make those other units seem universal.

I think your tendency to jump in with hurried replies is the problem here. In fact, I suspect you insert your replies even before you have read my whole argument. Or maybe you are reading with spectacles that are fogged up with impatient assumptions. Either way, you are not developing a coherent debate here. I'll be gracious and assume that you really are pressed for time. In that case, please reply only when you do have time. Lucretius 22:41, 29 September 2006 (UTC)

well, what you're bringing up is an entirely different issue. the premise of all of this (even from Planck's assertion that an E.T. could be expected to use the same units) is that we are able to communicate qualitative notions and facts (so we both have a comparable knowledge of nature) and numerical information. they understand gravity about the same as we do, we both know what 13 means (00001101 in binary), we can even communicate fractional numbers (as rationals or ratios of integers, if necessary).

but even if we could communicate this information and have a comparable understanding of physical theory, how could we describe to them how big/tall humans are, how big the planet Earth is, how fast it spins, how far we are from the Sun, how big the Sun is, how much radiant output the Sun has (or the solar radiant intensity at our distance)? we can't do it in terms of meters, kilograms, and seconds. they would have no point of common reference, not until we do it in terms of some chosen set of natural units. we could mutually agree on a set of natural units that use properties of some particles or simple atoms (like the hydrogen atom) as a common reference (such as atomic units), but if we do that, it would be silly to ask them how big the Bohr radius is because, by definition of our common reference, it would be the same for them as for us. but, given atomic units, we could meaningfully ask them what their speed of light is and if it is different than our speed of light, we know that α is different for them than for us and that is the salient difference.

but if we agreed to use Planck units instead, it would be meaningless to ask them what the speed of light is, but meaningful to ask what the electron mass (in terms of the Planck mass) and the Bohr radius (in terms of the Planck length) are. if m_e/m_P comes out to be the same number we have, but a₀/l_P comes out different, we will again know that their α is different. or vise-versa. if a₀/l_P comes out to be the same number we have, but m_e/m_P comes out different, we will again know that their α is different. α is the important quanity. whether we use atomic units and measure that c is different or use Planck units and measure that m_e or a₀ is different is not important. nature doesn't give a rat's ass. the salient difference is that they measure α to be different than us and for that reason, we know that life is different for them than for us. (or if α is the same number, we might think that the physical law for them is the same for us.) r b-j 23:14, 29 September 2006 (UTC)

Thanks RBJ. I don't disagree with this (I speak as an Earthling). In fact it has been our common assumption all along. You went off the rails earlier when we were talking about how to introduce Planck units to Zog and you brought up a varying fine structure constant - that condition made the whole task of communicating with Zog impossible since it deprived us of a set of units common to both Zog and Earth. However, my point all along has been that Zog might not know Planck units and yet could still be more scientifically advanced than we are. They could have developed a set of dimensions that unite all the fundamental forces without any reference to gravity or even electromagnetism. In short, it's a bit arrogant to assume that planck units are God's units. God could be a Zoggian. I would like to learn from Zogg, which is why I was really traumatized when you stuffed up the fine structure constant. It ruined my chances of finding out the truth. Now we have reached a happy ending but...a new thought has just popped into my head. What if the fine structure constant isn't embedded in the Zoggian dimensions? What then? We're stuffed in that case.

But to return to the original point of this debate - you need to rewrite the Invariant Scaling article. It's clumsily expressed, it overstates the non-dimensionality of measurements, it gives implicit support to Duff's extreme views. Measurements can be dimensionful without compromising invariance. Lucretius 05:09, 30 September 2006 (UTC)

okay, returnig to the original issue that you brought up - you believe that "[I] need to rewrite the Invariant Scaling [section]". this is an opinion that you have and have every right to have. two observations: i am not sure how many others share that belief. indeed, a credible physicist (Baez) said it looked okay to him and edited a minor part of that very section very recently. he's not complaining.

secondly, you attempted to bring up physical justifications to support your objection to it, but that hasn't succeeded either. i actually feel you were making red herring arguments. using the scenario of the Zoggians (which is not used in the article, nor should it be), of course there are problems (the speed of communication can't exceed that of light, having a common basis for communicating any concept or basic fact is problematic, i'm sure there are people a lot smarter than either of us thinking about how that might be done). but if we were able to communicate with the Zogs qualitative fact and numerical information (like if they spoke English and we could just simply talk with them and even show them things with a "PicturePhone") but they are over there and we are over here, we still need to identify some common points of reference to communicate physical quantity to them. now if, somehow, c or G or some other dimensionful physical constant was "different" for them than for us, there is no way for us to know that and communicate that to each other. but if α is different, that would count! we (and they) would know it.

this issue does not need Planck units to illustrate (and the Barrow quote does not use Planck units) and has found its way into VSL and Physical constants, but Planck units is useful for illustrating it and has been used which is one good reason Planck units is a concept to pay attention to. what is in the section you object to is an interpretation of that use of Planck units that is IMO and, i believe, other's opinion, faithful to the basic concept and is illustrative of it even if it uses an illustrative vehicle such as a hypothetical "god-like being" that somehow could sense the difference between different speeds of light. whether it's a "god-like being" or aliens on the planet Zog, the point is the same, in the final analysis humans or other non-supernatural physical things cannot measure or perceive anything but dimensionless quantities and it's only the dimensionless quantities that ultimately matter. if you think or measured that some dimesionful quantity has changed, that change can be traced back to a more fundamental dimensionless quantity changing. i know that Gabriele Veneziano agrees with Michael Duff on this one, and i think even Lev Okun (their disagreement is more esoteric). from other writings, i believe that John Baez, Frank Wilczek, and John D. Barrow do also. r b-j 19:55, 30 September 2006 (UTC)

Thanks RBJ. You've taken some care with this reply and I appreciate it. I diasgree with only a few things. You say the Zoggian stuff was a red herring. No, it was expanding the argument so as to further explore the issue of dimensions - do they have real physical significance or are they just abstractions. This is a big issue in the article - there it is a red herring because it has nothing to do with invariance. It became an issue in the article because of your reliance on an inappropriate reference - the debate between Okun, Veneziano and Duff. Worse still, the article slants the interpretation of measurements towards the Duff position. His argument that there are no dimensionful physical constants is completely supported by your argument that measurements are ultimately dimensionless. Not only is this basically irrelevant to the article topic but it is also, in my opinion, anti-science in its implications. A universe whose physical dimensions are mere abstractions is a universe better studied in a monastry than in a laboratory. Of course the article is so badly written that the world will never be influenced by it, but I still think you should be making an effort to tidy it up.

Anyhow, this has been my final attempt to get some changes made. Thanks for your willingness to debate the matter but I would rather you showed some willingness to change the article. Lucretius 23:25, 30 September 2006 (UTC)

Duff ain't saying "that there are no dimensionful physical constants", he is saying that the dimensionful physical constants ain't "fundamental", whatever that means (and Okun disagrees, i think). i think i understand what is meant. a fundamental physical constant is one that ultimately means something. the term i used in another argument is that it is a parameter of meaning in defining the nature of physics in the universe. the last count John Baez has is that there are about 26 of them and h, c, G, ε₀, or e ain't on the list (but there is a combination of 4 of those that is on the list). not only Duff and Baez say this, but John D. Barrow, Frank Wilczek and a bunch of other physicists you'll see on sci.physics.research that don't have Wikipedia articles about them also say this.

also, the article is not about whether or not time, length, mass, and charge are fundamentally different dimensions of physical stuff, it assumes they are as did Planck in deriving the Planck units. whether or not dimension of physical quantity is real or just an abstraction humans came up with to describe different quantities of stuff we come across is still not the purpose of the article, but i think it assumes that it is real. Still doesn't matter. we perceive time as a different thing than length (or spatial displacement). and we perceive mass as something else that is different than either time or length. whether it really is different or just that humans perceive it as different doesn't matter. the fact that we at least perceive this stuff as different means that we measure properties of free space, h, c, G, in terms of anthropometric units of this stuff and from these properties, define natural units of this stuff we call time, length, and mass that normalize those constants. that, in effect, defines a natural means of scaling time, length, and mass and as long as the size of stuff doesn't change relative to that scaling, nothing we know is different no matter what might have conceivably happened to h, c, or G. that's all that section is about. r b-j 05:06, 1 October 2006 (UTC)

Again thanks RBJ. Let me quote Duff, beginning at the bottom of page 22 of the relevant text:

"In the natural units favoured by the Zero Constants Party, there are no dimensions at all and hbar=c=G=1 may be imposed literally and without contradiction. With this understanding, I will still refer to constants which have dimensions in some units such as hbar,c and G as 'dimensionful constants' so as to destinguish them from constants such as a, which are dimensionless in any units."

I think maybe you were confused by Duff's references to 'dimensionful constants' - it looks superficially as if he accepts they are dimensionful - but as the quote shows he regards these as actually non-dimensional. Moreover, he says clearly there are no dimensions at all. The Invariant scaling article endorses this radical view by saying that all measurements are ultimately non-dimensional. I'm sorry RBJ but I can't put it more clearly than this and I don't want to keep repeating myself. If you still don't get the point then I must conclude that you will never get it. Invariance does not require us to accept Duff's particular point of view and the article should be phrased more moderately to take account of the opinions of all those (the majority) who believe that there are at least some dimensions and that at least some measurements are truly dimensionful.Lucretius 08:47, 1 October 2006 (UTC)

L, i am not confused. this quote is on p. 31 on my copy. try quoting the whole paragraph, and then tell me what it is that Duff is saying and contrasting to Okun. (it is literally what is done in the nondimensionalization section of the article. are you objecting to that also?)

L, i know you think you know of what you write, and before, despite the rigorous physics training an elementary school teacher gets in Australia, i thought so too, but am not so sure now. (it's not that in engineering we get this kind of deep physics, but we are taught the meaning of units, dimension of physical quantity, conversion factors, etc. i don't have time to deal with every misunderstanding you might have of what Duffs. r b-j 15:26, 1 October 2006 (UTC)

Dimensionless measurements 2

let's start a new section. i'm at home and using my system 9.1 Mac and i can't get Firefox for that version and IE (which sucks) limits my edit box to 32K. r b-j 15:30, 1 October 2006 (UTC)

We must both have rocks in our heads RBJ - you because you aren't thinking and myself because I'm still prepared to debate with you. I'll keep digging for a little longer in the hope that you are still breathing and that I can get you out from under all those rocks before you die. But I'm running out of hope.

I'll quote Okun, page 6.

"In such natural units all physical quantities and variables become dimensionless. In practice the use of these units is realized by putting c=1 hbar=1 G=1 in all formulas. However, one should not take these equalties too literally, because their left hand sides are dimensionful, while their right hand sides are dimensionless."

I hope you got past the first sentence. If you did, you'll see that Okun regards the non-dimensional equations as a mathematical fantasy that mustn't be taken literally. Duff on the other hand regards dimensions as a fantasy and he thinks the equations should be taken literally. Both Okun and Duff employ non-dimensional units but with very different interpretations. Okun's interpretation wouldn't shock anybody. Duff's interpretation is profoundly shocking (to most people, I believe). Just compare the two quotes I have given you and you should feel the load of rocks begin to lighten.

I have an image of you as a practical man and it is therefore difficult for me to believe that you would side with Duff rather than with someone like Okun. But, as I have said all along, their debate is actually irrelevant to the Invariant Scaling article, and the text shouldn't be referenced. You certainly shouldn't endorse Duff's views with statements about the non-dimensional nature of measurement. And you need to reword the article to make it clearer. Using as few words as possible is a good rule of thumb for the development of a lucid style.

Have you seen the light yet? Or is it too late?

I'll add this also, RBJ, as it might save time. Here is a quote from the Invariant Scaling article:

"the only quantities that we ultimately measure in physical experiments or in our perception of reality are dimensionless numbers. When one commonly measures a length with a ruler or tape-measure, that person is actually counting tick marks on a given standard or is measuring the length relative to that given standard, which is a dimensionless value. It is no different for physical experiments, as all physical quantities are measured relative to some other like dimensioned values".

Duff would subscribe to this passage, Okun and Veneziano would not. Duff thinks measurements are dimensionless ratios, the other two argue that measurements can be interpreted in that way but that they are ultimately dimensionful. Theirs is a subtle debate of profound significance. Your article simply bumbles into that debate like a bull trespassing on a minefield. Either you must add a disclaimer on behalf of Veneziano and Okun or, more simply, you remove any reference to their debate. Their debate isn't really relevant to the article as all three men subscribe to invariance. Lucretius 01:22, 2 October 2006 (UTC)\

you didn't quote the entire paragraph from the paper that i suggested. i was asking you to quote to whole thing (rather than just that one statement of Duffs that you don't like) and then tell us what you think it means. (i'll give you a hint: it means essentially what those five equations were that you insisted were worthless and deleted from the Planck units article.) you do that, and i'll tell you what Duff meant by saying in one sentence that "there are no dimensions at all" and in the next: "With this understanding, I will still refer to constants which have dimensions in some units such as ħ, c, and G as 'dimensionful constants' so as to distinguish them from constants such as α, which are dimensionless in any units." it's not complicated.

i have another suggestion, L: it's not just Duff. it's Baez, Barrow, Wilczek, and even Veneziano ("I also agree with Mike [Duff] that all that matters are pure numbers." - the disagreement he has with Duff is about what pure numbers are important). why don't you go to the newsgroup sci.physics.research or to the n-Catefory Cafe blog or another related thread? see what those guys tell you. there is debate about what parameters are important. there is virtually no debate that the net result of any physical measurement is dimensionless. the stuff you object to is essentially a tautology. tautologies don't say much but the trouble with disputing them is that one has to refute the entire premise. if one accepts the premise and disputes the "result" of a tautology, that person contridicts themself. that's why i have trouble understanding why any of this is controversial to anyone who actually understands the concepts.

i think i suggested that to you before. take your problem up with them. they'll set you straight. r b-j 03:48, 2 October 2006 (UTC)

This reply does not surprise me.

I deleted the 5 equations because they derived fundamental constants from Planck units. Planck units had already been derived from fundamental constants and I thought reversing the process was simply trivial. But if you want to restore those 5 equations by all means go ahead! Let them stand forever as a monument to your unique love of tautologies. There are more tautologies in the Invariant Scaling article than there are in all the psalms of The Old Testament.

Regarding the part of Duff's paragraph that I am supposed to have suppressed, I don't see the point you are getting at. It's simply a restatement of c=1.

Regarding Veneziano, I notice that he says the difference between him and the other 2 might simply be a difference in words. Words are important. Definitions are made from words and conclusions are often buried in definitions. My whole argument has been based on a scrupulous analysis of the words in your article and how they relate to the debate between Duff et al. Either you are incapable of understanding or unwilling to understand my concerns. You certainly haven't said anything to make me think that my concerns are unnecessary.

Finally, this argument clearly isn't going anywhere and we'll just have to agree to disagree. Cheers Lucretius 05:42, 2 October 2006 (UTC)

I forget to add one last thing, RBJ. Tautology is not a valid form of logical argument.

similarly to one of criticisms of the weak anthropic principle:

... which has been criticized, by its supporters as well as its critics, for being a tautology, stating something not readily obvious yet trivially true. The weak anthropic principle implies that our ability to ponder cosmology at all is contingent on all fundamental physical parameters having numerical values falling within quite a narrow range. Critics reply that this is simply tautological reasoning, an elaborate way of saying "if things were different, they would be different". If this is granted, the WAP becomes a truism saying nothing and explaining nothing, because in order for us to be here to ponder the universe, that universe has to be structured so that we can exist. Peter Schaefer denies that labelling the WAP a truism invalidates it, on the grounds that one cannot refute a statement merely by saying that it is true.

it depends on what you do with a tautology, L.

I'll show you how it caused your article to go off the rails.

yeah, right.

Quoting from your article:

"if all physical quantities (masses and other properties of particles) were expressed in terms of Planck units, those quantities would be dimensionless numbers (mass divided by the Planck mass, length divided by the Planck length, etc.)..."

So far so good. These quantities are dimensionless numbers because you have defined them as dimensionless ratios. But then, by way of tautology, you make these invalid transitions:

"and the only quantities that we ultimately measure in physical experiments or in our perception of reality are dimensionless numbers. When one commonly measures a length with a ruler or tape-measure, that person is actually counting tick marks on a given standard or is measuring the length relative to that given standard, which is a dimensionless value. It is no different for physical experiments, as all physical quantities are measured relative to some other like dimensioned values".

that was not extending the first statement into the second. i was not using the first statement (that you don't object to) as a rationale or justification for the second. they both are true on their own merits. (but i was using both to make the case that you are objecting to.)

These statements are wrong - when one "commonly' measures a length, and when scientists make scientific measurements, the measurements are in fact dimensionful.

that is a statement of ignorance. you name a single physical measuring device, even one as simple as our own biological human senses in which the net result of the measurement is dimesionful. as an engineer who has on multiple occuraces dealt with measuring devices (essentially that is what an analog-to-digital converter is), i, as well as any other engineer and physical scientist, know better.

again, would you like to take this belief of yours to Talk:Nondimensionalization? where the article says:

i didn't write that. would you like to take this on at that article?

But you seem to think these statements follow logically from the initial statement. That's where tautology gets you. Tautology is a rhetorical device, suitable for poetry but bad news for rational argument.

labeling something as true doesn't invalidate it, L.

I know this subtlety won't register with you but I figured it needed to be said. And that really is my final shot across the bow. Cheers. Lucretius 08:30, 2 October 2006 (UTC)

you need to ask yourself: why is it that the physicists haven't come over to Planck units and change that section? why is it that primary school teachers (or at least one primary school teacher with a commendable philosophical interest is this stuff) object, but the physicists seem to leave that section alone (a few mods, but they didn't delete it nor object to it here at the talk page)? why haven't you taken the physical insight that is the basis of your objection to either of those blogs or to the moderated newsgroup sci.physics.research? why haven't you done what i asked and quoted the entire paragraph of that Duff quote and tell us what that quote and its context mean? r b-j 16:10, 2 October 2006 (UTC)

Dimensionless measurements 3

Hi RBJ. I regret my bad manners in the previous section. Good manners are the clothes of good arguments and my arguments deserved better than that.

don't sweat it. -- r b-j

Adressing some of the issues you raised at the end, I've gone to a lot of trouble to quote the whole paragraph by Duff, just as you asked. In return, I would ask you not to keep inserting your replies into my text, a habit of yours that looks like an attempt to demolish an argument physically. If you can demolish my arguments through the force of your own arguments, well and good.

oooops. it's just that you make so many different points, each that deserves a response in it's own right. -- r b-j

Before I quote Duff, I'll answer another point you raised. You said that my objection to Invariant Scaling is based on a 'physical insight', as if it is my personal POV I am putting forward. My argument all along has been that the article does not represent the POV of the scientific establishment. Your article insists that all measurements are ultimately dimensionless and I say this is not the POV of the scientific establishment. It is instead Duff's POV in his debate with Veneziano and Okun. Your article references their debate and then endorses Duff's POV. The article is supposed to be about Invariant Scaling, which in fact does not require us to believe that all measurements are ultimately dimensionless. The reference to their debate is inappropriate and either you should remove it or you should at least include a broader definition of measurement to take account of the establishment POV, which is that measurements ultimately have a dimensional significance that cannot be ignored even when we argue mathematically c=1 or G=1 etc. Different people in the scientific establishment have different ideas about which dimensions are really significant, but almost nobody agrees with Duff that there are no dimensions at all.

Here is the paragraph from Duff:

"Incidentally Lev [Okun] objects that equations such as c=1 cannot be taken literally because c has dimensions. In my view this apparent contradiction arises from trying to use two different sets of measurement at the same time, and really goes to the heart of my disagreement with Lev about what is real physics and what is mere convention. In the units favoured by the members of the Three Constants Party [Okun] length and time have dimensions and you cannot therefore put c=1 (just as you cannot put k=1 if you want to follow the conventions of the Seven Constants Party [ SI ]). If you want to put c=1, you must trade in your membership card for that of (or at least adopt the habits of) the Two Constants Party [Veneziano], whose favourite units do not distinguish length from time. In these units, c is dimensionless and you may quite literally set c equal to 1.In the natural units favoured by the Zero Constants Party [Duff], there are no dimensions at all and ħ=c=G=...=1 may be imposed literally and without contradiction. With this understanding, I will still refer to constants which have dimensions in some units such as ħ,c ,G,k... as 'dimensionful constants' so as to destinguish them from constants such as α, which are dimensionless in any units."

As you see, there are a lot of different parties within the scientific establishment and they do not all argue that measurements are ultimately dimensionless. Thus length for instance can be understood as multiples of the Planck length and it retains dimensional significance for some theorists. For others, length is a ratio of some given length to Planck length and it is in fact dimensionless. The argument between Duff et al is really an argument about which dimensions are real in a universe measured in natural units, and which are not. For Duff, there are no dimensions at all and for him all measurements are ultimately dimensionless. Your article adopts this idiosyncratic POV as if it were the POV of the scientific mainstream. Lucretius 01:33, 4 October 2006 (UTC)

well, the argument, as i read the paper, is not about which dimensions of physical stuff are real and which are not, but more about which physical constants are fundamental and which are not. i certainly do not believe from reading it, that Veneziano disagrees with Duff about the fundamentally dimensionless nature of measurement (or perception) of physical quantity:

"I also agree with Mike [Duff] that all that matters are pure numbers."

by "pure numbers", i am quite certain that Veneziano means dimensionless physical quantity. i do not know if Okun agrees with that statement verbatim. he might not. assuming he does not, then Okun is saying that dimensionful physical constants like c and G are fundamental physical constants in the sense that they are parameters of meaning and physical theory, particularly, a theory of everything can hope to someday explain why those constant physical quantities are equal to the value that they are. if that is the case, it is not the POV of the physics mainstream in modern times.

the POV of the physics mainstream is that there are about 26 known dimensionless physical constants (most are about the Standard model) that are parameters of meaning whose values make a difference in how the universe and physical reality exist. not only do Michael Duff (and Gabriele Veneziano) take that position, but so does John D. Barrow, Frank Wilczek, John Baez (who have made public statements in print and/or online about it) and virtually every physicist who has commented about it on sci.physics.research and various blogs (two very recent blogs i have cited). whenever a cosmologist (Moffat, Davies, Davis, Magueijo) makes a VSL claim, the New York Times likes to feature them with an article, but the mainstream physics community either yawns or dismisses it, or people like Duff go after these guys with the persistant question: "How are you measuring this? How does it make any difference or have operational meaning?" i don't think you are representing the mainstream physics community accurately.

now, when i read that paragraph, where Duff says in one sentence that "In the natural units favoured by the Zero Constants Party [Duff], there are no dimensions at all and ħ=c=G=...=1 may be imposed literally and without contradiction" and in the next sentence "With this understanding, I will still refer to constants which have dimensions in some units such as ħ,c ,G,k... as 'dimensionful constants' so as to destinguish them from constants such as α, which are dimensionless in any units", i don't think i would come to the same conclusion of meaning as you apparently have. i'm pretty sure that Duff considers c as measured in units that are convenient to humans as a dimensionful physical quantity. indeed he says he does. what Duff is saying is essentially this:

now you, Lucretius, removed (and i didn't bother to fight it) 5 equations that you said were "pointless". the point they had was, for example:

$F = \frac{1}{4 \pi \epsilon_0} \frac{q_1 q_2}{r^2}$

with the "pointless" $\epsilon_0 = \frac{q_P^2 t_P^2}{4 \pi m_P l_P^3}$

means that

$F = \frac{m_P l_P^3}{q_P^2 t_P^2} \frac{q_1 q_2}{r^2}$

$F = \frac{F_P l_P^2}{q_P^2} \frac{q_1 q_2}{r^2}$

and eventually $F/F_P = \frac{(q_1/q_P) (q_2/q_P)}{(r/l_P)^2 }$

now this last equation is equivalently true, in any unit system, as the first one. but, of course, every fractional quantity shown is dimensionless, it is a ratio of a physical quantity expressed in whatever units to the Planck unit of the same dimension espressed in the same unit system. but the ratio is most certainly dimensionless. in that equation, we are expressing force, in terms of the Planck force, as a function of electric charge, in terms of the Planck charge and distance, in terms of the Planck length. that's what those ratios are. but F is still force in SI or cgs or whatever consistent units you care to dream up. same with q₁, q₂, and r. they are exactly the same F, q₁, q₂, and r as in the first equation.

but, in mathematics, we have this ability to do symbol substitution, and in this case, doing this is precisely what nondimensionalization is. we have every right to substitute: $F \leftarrow F/F_P \$ , $\ q_1 \leftarrow q_1/q_P \$ , $\ q_2 \leftarrow q_2/q_P \$ , and $r \leftarrow r/l_P \$ . no one can tell us we can't do that, and indeed physical reality doesn't give a rat's ass (Duff would substitute "fig" for "rat's ass").

so now we have: $F = \frac{q_1 q_2}{r^2}$

but this expression of physical reality is every bit as valid as the original equation up top. and this expression of physical reality has absolutely no reference to any human convention and it has no reference to what some would call a "fundamental" physical constant called the permittivity of free space. there is no permittivity of free space, it's not there. if God had a knob labelled $\epsilon_0 \$ and twisted it, the statement of physical reality would not change. you can do the same song-and-dance with $G \$ , $c \$ , and $\hbar \$ , but you can't do that to $\alpha \$ . even when you nondimensionalize, $\alpha \$ remains in the equations of physical law and if God twists the knob labelled $\alpha \$ , things would be different. if you wanted to, you could leave out one of those, say $\hbar \$ , and substitute the elementary charge $e \$ and say the same thing. so whether it's $c \$ or $\hbar \$ or $e \$ or $\epsilon_0 \$ that is left out of the list (and then appears to be changing when $\alpha \$ is changed), it doesn't matter it doesn't make any difference to how physical reality would be different. whether it's $c \$ or $\hbar \$ or $e \$ or $\epsilon_0 \$ that is changing when $\alpha \$ changes is only a matter of how you chose your units to measure things and, as Duff would say, nature doesn't give a fig what units you choose. the salient parameter that changed is $\alpha \$ or something directly proportional to it.

now, if you say that this is Duff's spin on things, i might agree with you. but if you say that it isn't the mainstream position of the physics community, then you are mistaken. not only is it the mainstream position of physicists, it is a tautology. you have to dispute the very premise:

$F = \frac{1}{4 \pi \epsilon_0} \frac{q_1 q_2}{r^2}$

or the very definitions of $l_P \$ , $m_P \$ , $t_P \$ , or $q_P \$ (or the "derived units") in terms of $c \$ , $G \$ , $\hbar \$ , and $\epsilon_0 \$ . if you accept the premise (the physical law expressed with dimensional constants) and the definitions of the Planck units in terms of those physical constants, and yet dispute that invariance, you contradict yourself. tautologies don't say much, they are a "vacuous truth" but a truth nonetheless (like the weak anthropic principle), but to dispute such a tautology (while accepting the premise of it) is logically fatal.

that is my spin on what Duff (and other physicists) are saying and i am not alone (despite the fact that no one has jumped into this on either of our sides). you're asserting that this is not mainstream. that's wrong. it's the contrary (VSL, etc.) that is not mainstream. you say that the mainstream scientific community believes that the net result of physical measurements is dimensionful; that's wrong (at least regarding the mainstream physical science community, i dunno what the psychologists and social scientists would say). we physical scientists (and i, as an electrical engineer, count myself as a physical scientist) who know the nature of physical instruments and metrology, also knwo that the net "raw" result of any physical measurement is a dimensionless quantity that represents the ratio of the measured quantity to a like-dimensioned standard that is a function of how the instrument was constructed. that standard might not be a single unit of that quantity, but, by virtue of its design, is a known multiple of such a unit and that known multiple is simply reflected in the scaling of the "tick marks" of the "meter" (or the equivalent in a digital readout). then when we attach the dimensionless "reading" of the instrument to the unit we are interpreting that readout with a dimensional concept. we say "that distance is 4.8 centimeters", but we counted 4.8 on the centimeter scale.

L, i don't think you're gonna win this. either on the merits of the physics or on the acceptance of whatever mainstream scientific community either of us can dredge up.r b-j 04:46, 4 October 2006 (UTC)

Hi RBJ. This is your most careful reply so far and I thank you for it.

Regarding "Oops" - I thought so: you appear to be inserting your replies before reading my whole argument.

Regarding the 5 equations, your account here was not featured with those equations. As I recall, one of those equations set the speed of light equal to the Planck length divided by the Planck time, and the others were just as trivial. As I said then, we could equally well divide my Compton length by my Compton time and the result would still be c. Am I therefore to form the basis of a natural set of units? Anyhow, the Planck units had already been derived from physical constants and therefore the equations, as they stood, were a waste of time.

Regarding the Okun position and dimensionful Planck units - the Planck length (as 1 unit of length), when divided by the Planck time (as 1 unit of time), is equal to a dimensionful speed of 1. This dimensionful speed is not somehow disconnected from dimensionless Planck units or from any dimensionless numbers that are parameters of meaning. Any change in the speed of light would still be a change in all the other quantities, all these changes would still offset each other and consequently we could still not measure any change in the speed of light - such a change is still 'operationally meaningless'. As I understand it, most establishment scientists accept invariance on terms such as these. They believe that at least some dimensions have real significance. Therefore some measurements are ultimately dimensionful. Duff doubtless accepts that measurements appear dimensionful in scientific experiments using conventional units that we have inherited, but I think he believes that the universe is ultimately measured in natural units, and these he believes are dimensionless. Measurements for him are therefore ultimately dimensionless. That also is the argument in your article -measurements are ultimately dimensionless. That is where your article is too exclusive in its interpretation of measurements because it shuts out Okun and others, for whom some measurements ultimately are dimensionful and who still subscribe to invariance.

That is how I see the situation.Lucretius 08:15, 4 October 2006 (UTC)

well, it's gonna be round the maypole again. don't have time. i gave it my best, L. i'm off to a San Francisco to an audio engineering convention. unless i have time, i doubt i'll be back here for a week.

ta-ta. r b-j 10:18, 4 October 2006 (UTC)

The bell went? OK. Round 3 has ended. There are still 12 rounds to go.Lucretius 21:11, 4 October 2006 (UTC)

Dimensionless measurements 4

Hi, RBJ. Here is a compromise. Please read it carefully before replying. And please do not insert your replies into my text. I make two suggestions:

1) Move the Duff et al reference to the Planck non-dimensionalization article, where it really belongs. You could even quote the Duff paragraph we've debated about - it points out that for some physicists (such as Okun) non-dimensionalization is a mathematical convenience that shouldn't be taken too literally, while for some like Duff it can be taken literally. That is where the reference to their debate rightfully belongs.

2) The Invariant scaling article includes a lengthy (I think too lengthy) explanation of invariance in dimensionful or physical terms (eg how the atom would change if a physical constant changed and how these net physical changes all cancel out). This physical explanation of invariance is not really consistent with the other argument you make that all measurements are ultimately dimensionless. If measurements are ultimately dimensionless, then ultimately there are no dimensions at all and who then gives a 'rat's ass' for physical explanations of invariance? Thus your definition of measurements (as being ultimately dimensionless) could also go into the non-dimensionalization article, though even there I think it needs careful qualification.

The problem with saying that all measurements are ultimately dimensionless is this - such a definition means we could equate 12 inches with 12 months. Even if measurements can be interpreted as dimensionless ratios they still refer to specific dimensions, and without that reference the measurements are nonsensical. Thus measurements in conventional units are ultimately dimensionful. When measurements are translated into a natural set of units, then we might validly enquire which measurements are really dimensionful and which are not, because some measurements are not always convincingly translated into natural units (eg Planck charge is defined in such a way as to allign it with the elementary charge and for me this is simply a mathematical expression without real dimensional significance). In the case of natural units therefore, you can choose to argue that some measurements are ultimately non-dimensional. Possibly you could even argue like Duff that measurements in natural units are all dimensionless i.e. 12 Planck lengths = 12 Planck times. But to argue, as you do, that the measurements we 'commonly' make, and those that are made in scientific experiments, are ultimately dimensionless - this is blatantly absurd. Lucretius 08:12, 6 October 2006 (UTC)

Ave atque vale, RBJ. I enjoyed our little debate. It occupied a few spare hours I had up my sleeve. Now I've rolled up my sleeves and gone back to work and like you I don't have much time for this any more. However I will try to answer any objections you might care to make to above argument. Hope you enjoyed San Francisco and all the people there with flowers in their hair (I expect there are more grey hairs than flowers in their hair these days). Cheers. Lucretius 06:58, 10 October 2006 (UTC)

Planck area?

I've just created a redirect to this article from Planck area. There's not actually any mention of a Planck area in this article, but that may be because there's nothing interesting to say about it once you've noted that it's the Planck distance, squared. At least, I assume that's what it is. If there's a better use for that redirect, or anything that needs to be said about Planck area... maybe someone will take care of that. -GTBacchus^(talk) 00:23, 2 March 2007 (UTC)

i (or anyone else) can add it as a derived unit. i think there is some more significance to the Planck area than that it is simply the square of the Plank length (just as there are some things behind the Planck mass and Planck force than the fundamental definitions). there is only one non-trivial reference to Planck area in WP. in the Bekenstein bound article, but i know i have run across the term somewhere. if you or someone else wants to write a short Planck area article, that would be nice. r b-j 00:46, 2 March 2007 (UTC)

A question

Could someone please explain to me why "In fact, 1 Planck unit often represents the largest or smallest value of a physical quantity that makes sense given the current understanding of physical theory."

I for example, have no problem thinking about time intervals shorter than the Planck time. For example, a time interval of zero seconds seems perfectly fine with me.

And for that matter, what is so non-sensical about talking about length scales shorter than the Planck length? As far as I know, we assume space to be continuous, no? Or, why is the Planck temperature the highest conceivable temperature? Sure, all the forces might be unified at that temperature, but that doesn't prevent me from imagining hotter things. --141.154.224.145 17:01, 30 March 2007 (UTC)

The handwaving explanation is that anything with enough energy to have a wavelength shorter than the Planck length has an event horizon bigger than the Planck length, so it's impossible to make something smaller than that size. If you have nothing smaller than that size, then you have no way to measure distances smaller than that size. You also get interesting uncertainty principle effects coming into play, giving you much the same result, if I understand correctly. You get the Planck time by considering the frequency of a particle with a wavelength of the Planck length (as trying to measure time intervals shorter than that ends up not giving meaningful results), and the Planck energy (and temperature) by considering the energy of a particle with the Planck wavelength (giving particles more than this amount of energy ends up not being meaningful). While you can _specify_ a length or energy larger or smaller than the limiting Planck value, things go badly wrong when you try to plug one of these values into the equations defining the way things in this universe behave.

I hope this answer is useful to you. For a more detailed answer, you'll have to ask one of the lurking physics-types. --Christopher Thomas 17:18, 30 March 2007 (UTC)

The question shows that you haven't quite understood the significance of natural units. In natural units, there is an intimate association between all kinds of dimensional quantities. The smaller is any natural length (wavelelength) the smaller is the associated time, but the greater is the associated energy and pressure. Thus times and lengths approaching zero are associated with energies and pressures approaching infinity. We can imagine infinite energy and pressure in some kind of abstract way but let's get real - you can't put an infinite amount of air into a tyre. Nature sets a practical limit to things. Planck units seem to be nature's limit to many physical quantities, as evidenced for example by the event horizon argument above. Lucretius 07:22, 31 March 2007 (UTC)

ET and Planck units

while i agree with User:Henning Makholm that any ET would likely not be using Planck units for anything practical, if there were to be any communication with ET (i think only one-directional communication would ever be possible, we might hear a message or we might send a message something like the Arecibo message), then the only reasonable system of units would be one of the Natural units of some form, possibly with some of these units adjusted by $\sqrt{4 \pi}$ or the reciprocal or some similar factor. we cannot expect to communicate any information to ET about how tall we are or how massive, or the radius or mass of our planet or the same for our star or the distance we are away from our star or our periods of rotation or orbit using any anthropocentric set of units. otherwise, we have nothing in common to base any common notion of scale. it is that sense of the word use that was meant in the article. and this has been in the article for a long time, well before i came upon it. r b-j 21:51, 5 April 2007 (UTC)

I don't think we disagree about the substance. The intention of my edit was to clarify the point made by the article (which I thought was phrased ambiguously), rather than to disagree with it. I have attempted a further improvement of the sentence in question now. –Henning Makholm 23:12, 5 April 2007 (UTC)

2006 CODATA values out now (at NIST site)

we might want to update the Planck unit values (in terms of SI) and some of the text. now the uncertainty for G is 1 out of 10,000 instead of 1/7000. i'm sure there are several other articles (like Physical constant) that should be updated. r b-j 17:27, 17 April 2007 (UTC)

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