Wikipedia:Reference desk/Archives/Science/2023 June 9

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June 9

Expanding universe and inertial frames of reference.

So the contemporary thinking is that space itself is expanding and the expansion is also accelerating.

So what are the implications for inertial FOR? If I choose any point in space, and thus all points around this point accelerate away from me isotropically, gravity aside, doesn't this mean that any given point in space is still an inertial FOR? Can it not be legitimately thought of as the classical "stationary FOR" for the purpose of most, if not all, physics calculations? Byron Forbes (talk) 05:56, 9 June 2023 (UTC)

Does our article Proper frame, usually called "comoving frame" in the context of the expanding universe, help to clear up some confusion? Just like an atlas with flat maps has only limited use in describing a spherical Earth, so do Euclidean frames of reference have only limited use in handling the reality of a curved spacetime.  --Lambiam 09:13, 9 June 2023 (UTC)

No.

My specific question here, is that due to any given point in space having all points around it accelerating away uniformly and isotropically, cannot any point be thus a legitimate inertial FOR? In fact, if we ignore gravity, then any given point can be thought of as the universal FOR. Byron Forbes (talk) 10:16, 9 June 2023 (UTC)

A single point cannot be a frame of reference. Any single point of space at a single point of time, i.e. a point in spacetime, can serve as the origin of a frame of reference.  --Lambiam 13:21, 9 June 2023 (UTC)

I believe you are exactly wrong.

If you think about this, all physics problems are solved by points in space. They are typically thought of as belonging to a "frame", but that is ultimately irrelevant because they are entirely able to define their "frame" all on their own.

For example, typical physics problems involve length, which is, of course, a measure between 2 "points" that may or may not be in the same FOR.

Any point in space is a self defining FOR. What other points around it are doing is irrelevant in terms of its specific FOR. Points around it may or may not be a part of the same FOR. But in an expanding universe, that is NEVER the case anyway!

Again, I will argue that any given point in space, assuming the region is generally not accelerating, is an inertial FOR. Especially in the case where all points around it behave uniformly and isotropically, as is the case with expanding space. Byron Forbes (talk) 05:17, 10 June 2023 (UTC)

I am not sure that you understand the concept of a frame of reference. The statement that "all physics problems are solved by points in space" is utterly devoid of meaning. The concept of spatial distance between two points in spacetime requires a common frame of reference. Any point in spacetime admits a continuum of possible frames of reference. The Minkowski metric of special relativity, which can be generalized to a Lorentzian metric in general relativity, does not require a specific frame of reference, but it is not a measure of spatial distance. To use it for that, you again need to choose a specific frame of reference.  --Lambiam 07:38, 10 June 2023 (UTC)

So are you saying that a "point" cannot be a FOR because it has no dimensions? Byron Forbes (talk) 07:51, 10 June 2023 (UTC)

Points and coordinate systems belong to different categories. A language cannot be an airplane, not because languages do not have wings, but because languages are not physical objects. A point cannot be a frame of reference, not because it has no dimensions, but because a point is not a system assigning values to other points.  --Lambiam 14:26, 10 June 2023 (UTC)

A typical FOR is a plane, which is merely a collection of points. I fail to see how any point in any FOR isn't a FOR itself.

Are you aware where I'm headed with this ------> proof that cosmological red shift is a violation of CoE? Is that what you're defending or do you really believe a point cannot be a FOR? :) Byron Forbes (talk) 05:04, 11 June 2023 (UTC)

Lambiam is correct for a point can serve as an origin or a point of reference and not as a metric of a metric space. Prior to SR, all distances are invariant in all reference frames and one can apply a Galilean transformation. However Einstein's spacetime dispenses with that, of course, but that does not mean it cannot be resurrected. Modocc (talk) 20:16, 10 June 2023 (UTC)

EM waves and photons.

I think everyone is well aware of the lovely diagrams we have for the above mentioned - beautiful blue and red sinusoidal waves perpendicular to one another and propagation, and in phase, right?

This notion normally comes from an antenna which produces E dipoles via AC current. So when the dipole is at a max so is the E field, but there is zero current and the B field (Ampere's Circuital Law) = 0.

So how do we get in phase E and B fields as per the lovely diagrams?

I have seen it said that the generated E field magically produces the B field, but that would be a curl and still not in phase anyway, right? Because when the E field is at a max, its rate of change = 0 and thus no B field, curl or otherwise, is being produced.

What am I not seeing here? Could someone please point me to some information that can clean me up on this issue? TIA. Byron Forbes (talk) 07:31, 9 June 2023 (UTC)

The Maxwell–Faraday equation $\operatorname {curl} ~\mathbf {E} =-{\frac {\partial \mathbf {B} }{\partial t}}$ relates the spatial variation in the electric field to the temporal variation in the magnetic field.  --Lambiam 09:06, 9 June 2023 (UTC)

Sorry, but I'm failing to see how a curl E field plays any role in a resultant perpendicular field.

An explanation I just saw was that due to the changing E field of the E dipole, you get a curl B field. But this happens when the current = 0. As the current increases, we get a curl B field then due to current, so such an explanation has an eternal curl B field. Byron Forbes (talk) 10:04, 9 June 2023 (UTC)

When the curl operator is applied to a field, the change in the operand in any plane produces a vector component that is orthogonal (perpendicular) to that plane.  --Lambiam 13:29, 9 June 2023 (UTC) Yes. Here is a link to Curl_(mathematics). Philvoids (talk) 16:00, 9 June 2023 (UTC)

Not sure what you're getting at here. If you are referring to a curl E field produced by the curl B field (from the antenna) then you get E fields also in and against the direction of propagation - i.e. you get a mess.

Let me re iterate the obvious error here.

It is assumed, wrongly, that when the E dipole in the antenna is maximised, that this then produces a changing E field (with a max rate of change), thus producing a curl B. So this has the B and E fields maximised at the same time. The mistake here is that curl B fields are produced by moving charges, not changing voltages. This is a widely misunderstood thing. The curl B field has no interest in electron acceleration or how much voltage might be being applied to it - it is only concerned with charge speed and the rate of dipole change, especially relevant in a wire due to electron movement relative to nuclei.

But it is also clear that the current = 0 at this time and thus no curl B field (Ampere) is produced by that. But now the E dipole starts to collapse, current rises and so does the curl B field (Ampere), so this means that one curl B field is dropping off and the other one (Ampere) is increasing, resulting in an eternal Curl B field.

This is simply wrong. Maxwell got it wrong and the world is yet to fix it!

This is very basic stuff. Byron Forbes (talk) 06:01, 10 June 2023 (UTC)

I can't follow this. You stated that you failed to see how a curl E field plays any role in a resultant perpendicular field. I pointed out that curl E, being the field resulting from the spatial variation in E, is componentwise perpendicular to the variation. If that is not what you failed to see, it might help if you used the language of mathematics, such as commonly used by physicists to communicate ideas, to make your questions less ambiguous. X plays a role in Y if they co-occur in some law of physics, unless Y denotes a constant.  --Lambiam 07:21, 10 June 2023 (UTC)

So you're deliberately avoiding the essence of this?

How do you explain the eternal curl B field? First, apparently produced by the changing dipole when current = 0, and then, 1/4 of the AC phase later, legitimately produced by Ampere's Law due to max current?

Is there some Law I don't know about that goes something like "The Law of ignoring Ampere's Circuital Law"? Byron Forbes (talk) 08:04, 10 June 2023 (UTC)

................or let me try this.

When the B field is at a max its rate of change = 0 ---------> curl E = 0

When the E field is at a max its rate of change = 0 ---------> curl B = 0

In no universe do you get in phase fields, even taking the curl mess out of consideration. Byron Forbes (talk) 10:41, 10 June 2023 (UTC)

curl B = 0 does not imply B = 0. --Wrongfilter (talk) 10:44, 10 June 2023 (UTC)

So where do the B and E fields come from? Byron Forbes (talk) 11:05, 10 June 2023 (UTC)

If you want to see how confused the world is on this, go and take a look on youtube.

There are lecturers portraying this in utterly ludicrous ways with glaring mistakes. One of them has the + and - charges of an antenna's dipole passing each other at the middle and says the current = 0 at that time! It's as though he is trying to trick us by having the + and - cancel each other resulting in 0 current (LOL). It is simply mind boggling! Byron Forbes (talk) 11:19, 10 June 2023 (UTC)

Btw, could someone tell me if referring to a Youtube video is against the rules without providing a specific link? Byron Forbes (talk) 11:22, 10 June 2023 (UTC)

It's OK to provide Youtube links on this desk. Modocc (talk) 20:21, 10 June 2023 (UTC)

Tried that - they got knocked back. Actually, the link somehow got changed to "Youtu.be" which is blacklisted (shrugs) Byron Forbes (talk) 02:13, 11 June 2023 (UTC)

https://www.youtube.com/watch?v=bwreHReBH2A&t=411s

See anything wrong here? Check out 6:52 - could he possibly be just making a simple mistake like this?Byron Forbes (talk) 02:23, 11 June 2023 (UTC)

"So where do the B and E fields come from?" These fields are two components of the electromagnetic field, which has a value at every point in spacetime. The electromagnetic field has been an aspect of the universe since space and time began, just like the gravitational field. It is everywhere, and where there is an electromagnetic field, there is also an electric field and a magnetic field. They are everywhere. Where did these fields come from? That is a good question, which might be answered if we knew where the universe came from. Who ordered it? Why is there anything at all?  --Lambiam 14:02, 10 June 2023 (UTC)

It's hard to believe you're not dodging the subject.

My question is simple - how do you get perpendicular, in sync E and B fields for EM waves and photons?

If anyone could start from the beginning and walk us through that it would be greatly appreciated. Might want to have a look at this brilliant attempt for reference! https://www.youtube.com/watch?v=bwreHReBH2A&t=411s Byron Forbes (talk) 02:19, 11 June 2023 (UTC)

@Byron Forbes @Hosh1313: Volunteers at this desk are not here to "walk you through" over 2 hours of video that you posted calling it "brilliant". The video explanation of E and B field propagation is not rigourous but slipshod when the presenter deliberately avoids Maxwell's calculation of the linked E and B fields in an EM wave. It is obvious that you lack an elementary schooling about Differential calculus with which to understand that curl is a differential Vector operator whose length and direction denote the magnitude and axis of the maximum circulation at any point of a distributed vector field, in this case an E field. That understanding is not likely to come to you by just watching a video and any arrogance on your part is inappropriate here with responder(s) who have likely spent somewhat more than 2 hours learning to apply Maxwell's calculus correctly in 3 dimensions. To explain the E and B dependance the "educator" in your video substitutes his hand-waved "right-hand rule" which is neither quantitative nor explanatory, and it is ruined anyway by the mirror-reversed trick photography he is using. A consequence of his over simplification of the speed "c" is that his example calculation of E_rms is wrong in the 4th figure. . I am not sure whether you understand that the right-hand term of $\operatorname {curl} ~\mathbf {E} =-{\frac {\partial \mathbf {B} }{\partial t}}$ means minus the Derivative with respect to time or "instantaneous rate of change" of field B. This and the curl are two of the differential operators used in Maxwell's set of equations. We are occupied here with Maxwell's model of E and B interaction that would be consistent with sinusoidal variation of both fields acting orthogonally, in phase and mutually supportive in a wave propagating through space, the electromagnetic wave. Further study of Maxwell's equations will find that they employ two constants permittivity and permeability that take values in a vacuum that predict the speed of the EM wave $c={\frac {1}{\sqrt {\varepsilon _{0}\mu _{0}}}}$. Other values of these constants lead to slower wave propagation through various media (with no "aether particles" ever involved). The confirmation of Maxwell's mathematical prediction came with the work of Heinrich Hertz who generated EM waves and proved that their velocity, polarization and refraction all obeyed the Maxwell equations. It is on this sound experimental basis that classical electromagnetic theory is founded. Philvoids (talk) 23:34, 15 June 2023 (UTC)

It seems my sarcasm was lost on you.

My use of the word "brilliant" was sarcasm since a few seconds into that video from the start time I posted, the lecturer claims that the current = 0 when the dipole = 0 which is absurdly wrong and that's how he went on to get the fields in sync.

Anyway....................... Byron Forbes (talk) 12:44, 16 June 2023 (UTC)

"If you start with incorrect assumptions, you may get interesting results." ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:50, 16 June 2023 (UTC)

References

Is there a probability consideration with an infinite number of possibilities?

Is there a case in the field of probability theory in which there are an infinite number of possible outcomes?
Normally there are only finitely many outputs, even if there are very very many outputs.
Is there a case of infinite possibilities, for example in quantum physics? 2A02:8071:60A0:92E0:9B9B:C02B:F5CC:22D1 (talk) 09:20, 9 June 2023 (UTC)

I can't help but think that if you allowed an infinite number of outcomes, the probability of any specific outcome is one over infinity, which is absolutely zero. So, no outcome is possible. 97.82.165.112 (talk) 11:12, 9 June 2023 (UTC)

An impossible event has a probability of 0, but the converse is not necessarily true; see note 1 in our article on Probability.  --Lambiam 13:16, 9 June 2023 (UTC)

There are at least two ways this can be done.

A random selection from a continuous distribution, such as the real numbers in the interval [0,1], gives an example where the probability of any specific value is zero, even though every event will produce a value in the range.

Alternatively, set up a probability distribution over an infinite number of discrete values, such as selecting natural numbers n (integers from 1 upwards) where the probability of n p(n) = (1/n) - (1/(n+1)). This gives a total probability of 1, and assigns every outcome n a non-zero probability, eg p(1) = 1/2, p(2) = 1/6 and so on.

(This really belongs on the Mathematics ref desk.) -- Verbarson  ^talk_edits 12:00, 9 June 2023 (UTC)

Mathematics has no problem dealing with continuous probability distributions, such as the standard normal distribution and the standard uniform distribution. This requires an approach to dealing with arbitrarily, even infinitesimally small quantities in a rigorous way. This cannot be done for physical systems; the laws of physics (including quantum physics) as we know them break down at the Planck scale.  --Lambiam 13:10, 9 June 2023 (UTC)

I see two problems: (1) Bertrand paradox (2) the problem with mesure of sets with cardinality like IR. 2A02:8071:60A0:92E0:9B9B:C02B:F5CC:22D1 (talk) 13:37, 9 June 2023 (UTC)

What are the as-yet undiscovered trailing decimal digits of transcendental numbers such as π and e? Philvoids (talk) 14:54, 9 June 2023 (UTC)

0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. (All the right numbers, not necessarily in the right order.) -- Verbarson  ^talk_edits 15:34, 9 June 2023 (UTC)

How much space do you need to type the right number (with the right digits in the right order)? Philvoids (talk) 16:53, 9 June 2023 (UTC)

There is no proof that any of the digits in the not yet computed parts of the decimal expansion of π is a digit 7.  --Lambiam 07:08, 10 June 2023 (UTC)

Mathematicians generally believe that the decimal expansion of π contains every finite sequence of digits. Philvoids (talk) 18:16, 10 June 2023 (UTC)

The Poisson distribution is an example of a discrete probability distribution that has an infinite number of possible values, the nonnegative integers 0, 1, 2, etc. Each value ≥ 0 has a finite probability greater than zero. This distribution often comes up in many fields of science. --Amble (talk) 16:13, 9 June 2023 (UTC)

An even simpler example is the number of times one needs to flip a fair coin before heads comes up. Even if you have flipped the coin 999 times, and each time tails came up, there is no guarantee heads will come up the next time. The probability is only 50%, also after 999999 tries, or 999999999 tries. So any positive integer is a possibility. The distribution is the (shifted) geometric distribution of mean 2.  --Lambiam 14:17, 10 June 2023 (UTC)

Of course. Pick an integer randomly. Theres 0.5 probability it is even, 1/3 that it divides by 3 without reminder etc.

Zarnivop (talk) 20:31, 10 June 2023 (UTC)

You have to specify the procedure how the integer is picked "randomly". If you ask all your friends to pick an integer randomly, I bet none will pick an integer that is greater than googolplex. Yet almost all integers are greater than googolplex.  --Lambiam 21:31, 10 June 2023 (UTC)

I always tell my students that all natural numbers are small - after all, for any given number there are only finitely many smaller ones, but an infinity of larger ones ;-). --Stephan Schulz (talk) 09:22, 11 June 2023 (UTC)

If you roll an infinite-sided die infinitely many times, the odds of ever rolling infinity are exactly 1-1/e, which is slightly worse than two out of three.  Card Zero  (talk) 21:29, 10 June 2023 (UTC)

While the odds of rolling an $n$ in $n$ tries on an $n$-sided die equals $1-\left({\frac {n-1}{n}}\right)^{n},$ and $\lim _{n\to \infty }1-\left({\frac {n-1}{n}}\right)^{n}=1-e^{{-}1},$ I think that the statement about rolling an infinite-sided die has no mathematical meaning.  --Lambiam 21:39, 10 June 2023 (UTC)

It is written that a million-to-one chance crops up nine times out of ten. -- Verbarson  ^talk_edits 21:45, 10 June 2023 (UTC)

What is the mechanism of action of Basil in mildly reducing blood pressure?

The only food I know that works for some people around the world (and worked for me personally) in mildly reducing blood pressure is the Basil plant.

Dietary supplements containing high concentrations of dried Basil leaves are also being sold and marketed as mildly reducing blood pressure.

If indeed I am correct and basil plant eaten raw (or maybe also dried) significantly but mildly reduce blood pressure, what is the mechanism of action?

Thanks. 2A10:8012:17:CDC6:E886:F0E4:683B:2264 (talk) 14:12, 9 June 2023 (UTC)

Basil contains eugenol, a plant-based antioxidant that may help reduce blood pressure by acting as a natural calcium channel blocker.^[1] It also contains hexane, that reduces levels of circulating catecholamines and diminishing vascular resistance.[2] The effects were temporary, lasting two minutes before returning to normal.^[3] More details here. --136.54.99.98 (talk) 16:18, 9 June 2023 (UTC)

I'm reluctant to answer this question since it seems to be getting awfully close to medical advice given what the OP has said. But I would note that basil when consumed as a dietary supplement should probably be treated fairly different from basil consumed as part of food. Basil is generally used as a herb which a number of people find pleasant. If basil is used in food, this may change the types of food consumed or at least may change some aspects of the food such as the amount of salt (or other sources of sodium) added. These changes could be the source of any change in blood pressure rather than anything to do with the basil itself. (These sort of confounding factors are one of the reasons attributing any observed health change to some specific part of the diet is generally very complicated.) Nil Einne (talk) 13:34, 10 June 2023 (UTC)

Comparing improvements in task performance

The improvements in task performance by AI models on benchmarks tend to be reported in recent papers as percentual correctness increases. Suppose two teams are reporting on their work. Team A reports an increase from 64% correct to 80% correct, which is reported as an improvement of 25% (0.80/0.64 = 1.25). Not bad. Team B reports an increase from 40% correct to 60% correct, which is reported as an improvement of 50%, so that should be even more impressive. But you can also present this as, for Team A, a decrease from 36% wrong to 20% wrong, reducing the wrong responses by 44%, whereas Team B achieved a decrease from 60% wrong to 40% wrong, reducing the wrong responses by only 33%. Are there publications that discuss the methodology of comparing such improvements?  --Lambiam 21:02, 9 June 2023 (UTC)

On the precarious assumption that every answer can be classed unambiguously as "right" or "wrong", a method can be used similar to the test for telepathy done using Zener cards (five groups each of five like cards). Each card contains an image of either a circle, cross, square, star or wavy line. The 25 cards are shuffled. The subject is then asked to give the identity of each card. A score of 10 correct out of 25 indicates some form of telepathy and higher scores show higher ability. Philvoids (talk) 21:57, 9 June 2023 (UTC)

Interpret "wrong" as "not correct". The question is not about assigning scores, but about comparing improvements of what in the Zener card test would be different subjects. If Alice scored on the average 16 last week but this week 20, while Bob scored 10 last week but now 15, both showing impressive improvements, which of the two had the more impressive improvement?  --Lambiam 06:52, 10 June 2023 (UTC)

Cardrew is more impressed by Bob's improvement than Alice's improvement because Bob got off to a weak start while Alice obviously entered as the stronger player from whom relatively more should be expected, and that expectation should rightfully be quantified in Handicapping as implemented with the mathematical precision that fairness demands in many competitive sports ^{* * * * *} . Dolores is most impressed by Alice's achievement of the highest score yet seen and she protests at the Misogyny revealed in this, yet again, rampant barefaced attempt by Patriarchy to devalue and belittle downtrodden Alice because of her gender. My friends Dolores and Cardrew are so upset by your divisive scenario that exploits unsourced information about two living persons A---- and B-- that we may have to call on Edward, whose qualifications in Impressionism are often demonstrated at parties, to resolve your question about perceived impressions that can only be answered in the realm of Subjectivity. Philvoids (talk) 16:23, 10 June 2023 (UTC)

The question was actually not about your eminently qualified friends and their perceived impressions, but about the existence of publications that discuss the methodology of making such comparisons. That may include publications that give the advice, "Don't even try."  --Lambiam 17:26, 10 June 2023 (UTC)

Hahaha yes this is a very real question for schools where they want to say how improved a child is by a teachers tuition, and it affects the schools ratings for parents and can influence the amount of money they get, see for example [4][5],[6]. And their answer? It depends! I'll be intersted if you get a good answr! NadVolum (talk) 17:44, 10 June 2023 (UTC)

“An Extensive Comparative Analysis of Chatbot Technologies” This paper compares three chatbots: chatGPT, Google BARD, and Microsoft Bing in natural language processing, machine learning, and user experience. “Comparative Analysis of Chatbots” This paper analyzes and compares the total accuracy score of eight chatbots based on the answers provided by them to a set of predefined questions. Future directions for chatbot research: an interdisciplinary research agenda. Philvoids (talk) 18:40, 10 June 2023 (UTC)

The paper compares accuracy scores; it does not compare improvements.  --Lambiam 21:53, 10 June 2023 (UTC)

Methodology does matter and their scores are a statistical sample subject to all kinds of caveats, such as being very small as is, but for comparison purposes this question falls under effect size. Skimming the article I found this observation "Since rather large probabilities of passing were used, there is a large difference between relative risk and odds ratio. Had failure (a smaller probability) been used as the event (rather than passing), the difference between the two measures of effect size would not be so great." Modocc (talk) 22:46, 10 June 2023 (UTC)

Thank you, that is extremely relevant. Clearly, there are a plethora of metrics to choose from. There are statistical handbooks that give practical methodological advice regarding the choice of an appropriate test from the plethora of statistical tests. One might hope for a text giving practical methodological advice to researchers who need to choose an appropriate metric for comparing effect sizes.  --Lambiam 10:48, 11 June 2023 (UTC)