joigus
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Posts posted by joigus
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On 2/13/2024 at 9:31 PM, ahmet said:
beauty simply means me. absolutely.
Oh I get it. Is it 'beautiful', 'praised', 'commendable'? I've read different translations.
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21 minutes ago, Genady said:
Are you sure? I seem to remember (I think, from Shankar's lectures, but would need to look back to make sure), that force is defined first statically, like the following. Take a spring. Some force needs to be applied to stretch it say by 10 cm. Take two identical springs like that attached parallelly. A force needed to stretch both of them together by 10 cm is defined as double the first force. Etc. After force is defined in such a way, its use in dynamics is a law / equation.
Well, good point. It's a bit subtler than what I said. I do remember a similar operational definition to what you say in Mechanics by Keith R. Symon. But even for your operational definition of force, you need to set a unit of mass. So it's kind of circular. Mass helps you define force, while you need a standard of force to define mass. They're tied to each other, really.
Let me put it in my words: If you think it makes sense to fix a standard of force independent on anything it acts on, to that extent, you can define mass. If you think it makes sense to fix a standard of mass independent of the force that acts on it, then you can define force. It could be more complicated. It could be that there is no way to abstract the 'push or pull' that you exert on a body from the parameters that define the body.
Maybe it's something closer to what I called a formula (mathematicians use that distinction, I know). What it is not is an equation, unless you use the formula to plug in numbers and solve for the unknown, of course.
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35 minutes ago, jajrussel said:
I looked up Ubi materia ibi geometria also
Those were words by Kepler. It's Latin for 'wherever there is matter, there is geometry'. It goes to prove that the idea that geometry held the key to understanding physics has been around for a long time. The factoring out of one of the masses from the equation of motion (or the fact that you could talk about gravitation without without one of the masses not really being there, and the other being replaced by energy, as Genady suggested) is a subtle clue that geometry is at the core of gravity.
As to push or pull, I think you mean something about attractive vs repulsive forces perhaps? But then it's not about F=ma vs F=GmM/r².
F=ma is the definition of force. It's a definition, rather than an equation really.
F=GmM/r² is a law of force, and it has a very different content.
It's when we equate both, as @Janus illustrated,
ma=GmM/r²
that we do have an equation, ie, an equality to be solved. The mere F=ma cannot be solved. Definitions cannot be 'solved'.
Not all equalities are equations. This is a common misconception. There are definitions, identities, formulas and equations.
Definition: velocity=space/time
Identity: x²-y²=(x+y)(x-y)
Equation: x²-2x+1=0
Formula: (c1)²+(c2)²=h², where c1 and c2 are the catheti of a right rectangle and h is the hypotenuse of the same triangle
A definition is just a labeling, an identity is an algebraic equivalence that's always true, an equation is the expression of a hypothesis to be solved from its statement in the algebraic language, and a formula is an algebraic statement involving ideas that can be abstract, geometrical, etc.
There is a long tradition of calling physical laws, definitions (and perhaps formulas) all 'equations', which might be at the root of your confusion.
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2 hours ago, Genady said:
Right. It is not there to start with. 😉
Ubi materia ibi geometria
Einstein took it to the next level. 👍
10 minutes ago, jajrussel said:So there is a distinction there is F=ma push
then there is F=GMm/R2 pull
push/pull is not a physical distinction. It's anthropomorphic.
'Work' is another anthropomorfic term, although extremely useful. But push vs pull is not useful at all in terms of physics.
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We should all be amazed that this little m disappears from the equation. It goes very deep in the nature of gravitation.
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1 hour ago, Oryza sativa said:
Quantum events are fundamentally probabilistic. so no matter how well you knew the initial situation you could not predict the outcome.
Not true. That depends on how you prepare the initial situation and what you want to measure. Some outcomes you cannot predict. All the outcomes compatible with the eigenstate you have prepared (AKA 'knowing the initial situation') can be predicted with 100% accuracy.
But I have the feeling that something, very much related to information, is becoming quickly unavailable on this thread.
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2 hours ago, Oryza sativa said:
If Entropy is increasing then information in universe is also increasing.
This is wrong. As @exchemist said, entropy does not represent the total information, but only the part that your description "cannot see".
Say you have 2 grams of hydrogen. This is about 6x10²³ molecules. The number of coordinates in phase space (positions and momenta) of this system is about 3.6x10²⁴. All of this is information, and this information is never lost. In theoretical physics that's called microscopic entropy, or also volume of phase space. The fact that it is a constant is called Liouville's theorem or "conservation of phase-space volume", or "conservation of information", or "conservation of the number of distinctions".
Now, usually you want to describe that sample of matter, not in terms of all the molecular coordinates, but in terms of a reduced number of parameters: pressure, volume, temperature, internal energy, and so on. It is because you can do that for all relevant purposes that this entropy that we use in thermodynamics becomes relevant. It is this entropy the one that always increases.
In the case of a BH, something similar happens. The BH is described by just (M, Q, J) --mass, electric charge, and angular momentum. Yet, it must have some microscopic degrees of freedom that account for this thermality.
It's not so clear to me what you mean when you say,
2 hours ago, Oryza sativa said:So, Hawking's radiation being very high entropy, should hold most quantum events of the universe.
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13 minutes ago, ahmet said:
no I did not say I have no academic background. I said I have no formal academic background. This are not same.
Oh well. That probably changes everything then.
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3 hours ago, ahmet said:
ok. continue to act in that way. you will eventually learn how it is.
This did come across as threatening. I take it that's not what you meant, but it did sound like that.
3 hours ago, ahmet said:joigus, what is your personal idea?
should I reject the invitation?
Ok. Yes. That's my personal idea. You say you have no academic background and a prestigious journal asks you to referee for them? Seriously?
It's like when a very hot young lady asks me to contact her on FB. Do you seriously think life is just that kind?
I'm just trying to be helpful here. And Bufofrog probably was too, although by using humour.
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9 hours ago, ahmet said:
a wery well known brand of journal group's member journal today has sent me an invitation to assess a manuscript. I am investigating the reason why for the case.
have an idea?
If you don't have a previous trajectory as a referee for anything in the way of 'well known brand of journal group's member journal', I would suggest you might just have been targeted for a phishing attempt, and you should be careful. There are other less dangerous attempts to scam you that would look very much like that.
The very fact that you feel compelled to 'investigate the reason for the case' suggest to me there might be something 'phishy' behind this.
It's just a gut feeling. I hope none of this negatively affects anyone.
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1 minute ago, KJW said:
What I meant was: to what symmetry does charge conservation correspond?
Global phase invariance. IOW,
\[ \psi\rightarrow e^{i\alpha}\psi \]
where \( \alpha \) is a constant phase shift in the wave function. You can easily prove charge is conserved via Noether's theorem if you have a Lagrangian that produces the equations of motion.
It's the global version of gauge invariance. When you have local gauge invariance, not only gauge charge is conserved, but a field has to step in to guarantee it is preserved. And god says,
Let there be light,
Let there be gluons,
Let there be Z and W bosons,
and (hopefully),
Let there be gravitons, even if nobody can calculate anything with them.
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4 minutes ago, KJW said:
To be fair, relatively few people are aware that charge is the result of a symmetry. Perhaps you could explain what that symmetry is.
I can do better than that:
https://people.math.harvard.edu/~knill/teaching/mathe320_2017/blog17/Hermann_Weyl_Symmetry.pdf
According to Hermann Weyl, something is symmetric when it looks the same after you change a condition.
The 'thing' is thus symmetrical under the change of such 'condition'.
A sphere is symmetrical under rotations around its centre.
A fly is symmetrical under reflection through a mirror.
The laws of physics are symmetrical under changing particles for antiparticles.
...
And so on
The usefulness of Weyl's definition stems from the fact that certain transformations can be expressed in very simple terms as functions of few parameters.
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On 2/7/2024 at 8:19 PM, Otto Kretschmer said:
I am not sure about this.
Muhammad's life is no better documented than the life of Jesus - all information about him comes from sources written over a century after his death (the first biography of Muhammad comes from ca. 750 AD while he died in 632 AD).
Confucius and Buddha aren't better documented either.
I'm glad you noticed. Two thousand years after and more than 2000 miles away from the alleged origin of the story (northern Iran & Uzbekistan for Al-Tabari and Al-Bukhari respectively). That's pretty far away from Mecca and Medina both in time and space.
Add to that the fact that 'muhammad' (MHMD in most Semitic scripts) just means 'the praised one' and we are pretty much where we are with many other founders of religions. Nothing much except the hope of human group from centuries upon centuries ago to become relevant on the grounds of a religious preacher who might or might not have existed even.
No religion should be taken seriously. But the more modern ones are the more ridiculously off-base. Take Scientology, for example.
5 hours ago, MigL said:It seems that P Crone now also rejects her former ideas.
Patricia Crone died some 9 years ago. Her book Meccan Trade and the Rise of Islam is just a pacient and meticulous gathering and exposition of facts as recorded from contemporary records from the 5th-6th centuries (and somewhat before) AFAIK.
She very patiently shows how and why the "centre-of-trade" theory of Mecca is a physical/historical impossibility.
Maybe aliens from Proxima-Centauri could have made Mecca a commercial hub of the Nabateans. Camels just couldn't have done it. All the Nabatean know-how couldn't make up for the fact that Mecca is about 1000 meters below the main route to Ta'if, and extremely inconvenient --to say the least-- to be any kind of rendezvous in the trade route.
Impossible. What other things happened in Mecca in the 6th century? We don't know. Trade certainly was not one of them. That's probably why Mecca appears in NO book from before the 9th century.
Crone got many death threats from that and decided to keep a low profile from then on. That's what I know.
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8 minutes ago, StringJunky said:
Never seen these before: ice flowers in Norway.
Beautiful! Thank you.
Here's the hook-up to why this happens:
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9 minutes ago, exchemist said:
Impossible. This was Theorist again. 🤪
Ah, so there's a history of the theorist...
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Ah, so OP maybe is trying to say, 'could the electron be there just because charges need to balance out?'
If that's the case, I know of a class of theorems called 'soft boson theorems' in QFT that say that something very weird would happen if charges didn't balance out at distances long enough, and that would make QFT inconsistent.
That alone wouldn't explain why the universe is not just a soup of photons from all the particle-antiparticle pairs having annihilated each other long in the past...
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On 3/23/2023 at 5:18 PM, splodge said:
In the present atomic model the atom consists of components but could the electron just be an elementary particles conservation of charge ?
Conservation of charge bears out an elementary symmetry. The electron is a carrier of that symmetry.
How could bilateral symmetry (a quality of a thing) be the thing itself?
Flies have bilateral symmetry. Is bilateral symmetry of a fly the fly itself?
Please, come to your senses.
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Where is the physics?
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2 hours ago, Otto Kretschmer said:
a strong emphasis on charity and support of free market
Ok. But slavery is allowed (halal), adoption forbidden (haram), sex with minors allowed (halal), etc, if political conditions allow. A lot of what you can or cannot apply from sharia depends on political climate, as stated clearly in the Qu'ran concerning taqiyya.
QuoteThe latest Global Slavery Index, produced by human rights group Walk Free, reveals the 10 countries with the highest prevalence of modern slavery are North Korea, Eritrea, Mauritania, Saudi Arabia, Türkiye, Tajikistan, United Arab Emirates, Russia, Afghanistan, and Kuwait.
From: https://reliefweb.int/ with my emphasis
I for one prefer Zoroastrianism, as long as you're careful with fire.
All religions are OK, I suppose, as long as you don't take them seriously --actually apply certain/a few/most of their principles.
All religions are OK if you reduce them to wearing of certain gear and handling of certain ritual objects and ceremonies. In that sense, they're not very different from a funny sport.
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7 minutes ago, TheVat said:
I don't want to disclose how long I believed that the Mohs Scale, of mineralogy, was derived from "Measure of Hardness Scale."
Some of these coincidences happen to be very useful as mnemonics.
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OP still looks like homework.
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11 hours ago, MigL said:
Some say you can notice this effect upon pouring liquid nitrogen into your cupped hand.
I've never been brave enough to try it.Would that be strictly German pricy SUVs ?
1 hour ago, J.C.MacSwell said:I would have guessed it had something to do with insufferable cold rather than heat...
Well the liquid nitrogen example that @MigL provided goes in that direction.
This reminds me of some quick notes on geometric optics concerning one such Lensmaker's equation, which led me to think something along the lines of 'Isn't it cute, that this equation was derived by someone called Lensmaker?' I soon realised of course, it was a typo or the author made a mistake, and it should have said 'lens maker'.
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On 2/1/2024 at 5:19 PM, Genady said:
And then, there is Freeman Dyson (F. Dyson, “The World on a String,” New York Review of Books, May 13, 2004)
The objection is expressed at 33:50 of the lecture I linked (without mentioning Dyson). If gravity were classical and gauge fields were quantum, you could beat the position-momentum HUP. Dyson's position basically is that Einstein's tensor is a classical field. But on the RHS of the equations you have the expected value of the energy-momentum tensor of quantum fields. You could, of course argue that there are <T²>-<T>² quantum fluctuations of these quantities, and thereby similar quantum fluctuations in the Einstein tensor.
On 2/2/2024 at 8:46 AM, ovidiu t said:I apologize. It mainly tries to solve AMPS paradox by EPR approach:
1. Entanglement of "space" in vacuum
2. Entangled Black holes (so it implies "un" entangled black holes)
3. Entanglement as a phenomenon generating/ creating spacetime
4. Entanglement quantum phenomenon bridging GR and QFT
I suppose the scientist needs no introduction. He's part of the team working/starting string theory.
Yes, ER = EPR is due to Leonard Susskind and Juan Maldacena. I don't know about the state of the art of it, but it's a way to deal with quantum gravity that's being explored recently.
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Force/ gravity/ mass/ acceleration
in Classical Physics
Posted
(My emphasis.)
There it is. There's your standard of force if you want to make the definition operational. The fixed spring is your standard of force. It's actually inescapable that one needs the other, as F=ma involves both and neither F, nor m, is a primitive concept with a direct observational interpretation, like time or space have.
I see no a priori reason to rule out a more complicated mathematical dependence like, say,
F=(m+C2m2+C3m3+...)a
with m being the additive parameter representing the "amount of stuff", F being our standard spring, C2, C3, etc, very small coefficients under a wide range of dynamical conditions, and the other force laws that we know and love later accomodating this complicated dependence. I'd challenge anybody to provide a robust argument why it cannot be that way.
Newton's choice is very sound and very natural, and harmonises wonderfully with symmetries, known behaviours, etc, but I see no a priori reason why it should be that way, and not some other.
I don't essentially disagree with anything Janus has said, by the way.