Moderators

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25310

2. ## iNow

Senior Members

375

21723

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336

44757

4. ## studiot

Senior Members

322

12427

## Popular Content

Showing content with the highest reputation since 08/07/19 in Posts

1. 8 points

## Rules update: bad faith discussions

Staff have decided to update the forum rules to include the following: This is in response to a number of threads and certain members who have made threads here under the premise of 'just asking a question,' only to reveal that they are in fact trying to peddle conspiratorial or otherwise nonsense ideas. While covered to some extent by pre-existing rules, we have decided to make it explicit that we will not be hosting these sorts of threads, if for no other reason than the fact that they are a waste of everyone's time.
2. 8 points

## Matter creates gravity

OK let's clarify something here. First consider the following definitions. Mass is resistance to inertia change Energy the ability to perform work. Spacetime a geometric model system with 3 spatial dimensions with 1 time dimension. In physics dimension is an independent variable or value that can change without affecting any other mathematical object. So how does mass curve spacetime. Well GR models bodies in free fall that is without any force applied. Time is given units of length and can be called an interval. This is done by setting c which is constant to all observers and adding a unit of time. So the time coordinate is given units of length by ct. $(t,x,y,z)=(ct,x,y,z)=(x^1,x^2x^3x,x^4)$ the last is in four momentum form for convenience as its useful to model a particle trajectory along the x axis. Now what is spacetime curvature. Well space is just volume... (Very important ) it isn't a stretchable bendable fabric... Those are just analogy descriptive. What spacetime truly means by curvature is the worldline paths for light it us the null geodesic. If you shoot two laser beams in flat spacetime those beams stay parallel. If spacetime is curved then the beams converge for positive curvature and spread apart for negative curvature. This is a consequence of how the mass term affects the time it takes for a particle to go from emitter to observer. That whole resistance to inertia. So let's drop two objects toward a planet. You have the usual Centre of mass. As the objects free fall they do not stay parallel. They will converge upon one another as they approach the center of mass. That what is really meant by curvature the free fall paths are curved. Not the volume of space.
3. 7 points

4. 6 points

## 1. Thermodynamic work

A question about a sign convention that leads to a lot of confusion. This is not the only instance multiple sign conventions in Science. In this case it is a result of History. Thermodynamics was originally developed by physical scientists and engineers. They were concerned with making machines (steam engines) for the industrial revolution. Steam engines are heat engines. That is they thought in terms of input (heat in the form of fuel) and output (work). Both of these were thought of as 'naturally being' positive quantities. So they wrote their version of the Law of Conservation of Energy (The First Law of Thermodynamics) as ΔU = q - w. Chemists came to the scene from a different point of view. They wanted all forms of energy to have the same sign, whichever side of the conservation appearance they appeared so they could present the equation as a sum on both sides of the equation. So they wrote their equation as ΔU = q + w. By then it was also realised that, although all the terms are energies, there is a difference between ΔU , which is a state variable of the system, and q and w which are exchange variables of the energies crossing the system boundary. So they tidied up by stating that all energies crossing the boundary from the system to the surroundings are negative and all energies passing from the surroundings to the system are positive. Now they could add them up, move them about in equations and between equations in other parts of Science in a consistent manner. It is an improved system But it shows the importance of knowing the sign convention in use and the equations that go with it. This last remark also applies to other such instances of multiple conventions such as those in Electricity, Elasticity and elsewhere.
5. 6 points

## Last post of the first 1000

This is my 1000th post! Time to celebrate, This is a fine moment to open the Islay Single Malt I got for Christmas. Cheers from Ghideon, to all new and old form members!
6. 6 points

7. 6 points

## My grand daughter!

My son holding my grand daughter!
8. 5 points

## Gravity

The 'bowling ball on a rubber sheet' is a two dimensional reduction of a 4 dimensional configuration. It has multiple problems, one of which is that you can observe it from an embedding third dimension. Space-time has no embedding dimension; both the bowling ball and you, the observer, would need to be intrinsic to the rubber sheet ( i.e. also two dimensional ). A three dimensional representation would already get rid of some problems, but not all. Picture a three dimensional grid, where x, y, and z axis divide up the space into cubic elements. A mass placed in this space would curve the x, y, and z lines such that the elements are moreskewed, and smaller, as you get closer to the mass. That is 'space' curvature, and one aspect of gravity, but already much harder to visualize than the two dimensional example of the bowling ball/rubber sheet. Actual gravity is four dimensional 'curvature' of space-time, and I can't help you visualize that as it is impossible. Some problems are just not suited to visualization, but understanding even just the basics of the math goes a long way to clarifying things.
9. 5 points

## Does Zoro produce enough aerodynamic lift here according to the Bernouilli's principle?

At which point, I have to post this: https://what-if.xkcd.com/1/ Spoiler: it doesn't end well
10. 5 points

## The world has changed...

The 'economy' is not just a money making mechanism for the wealthy, Phi. It is the means by which most of us feed, clothe, house ourselves and our families; it's how we survive. I have no problem with the economy 'going for a sh*t' as long as it saves lives. But if it 'goes for a sh*t' for too long, people start losing their life for reasons other than the pandemic. That is the balance that has to be struck; dying by starvation is just as bad as dying by Covid-19. I believe that is what Danijel Gorupec meant.
11. 5 points

## Today I Learned

Today I learned that skills improved by participating here on scienceforums can, at least in some minor way, be helpful in the current virus situation. I joined a local initiative where students studying from home can ask about math and physics. Debating science here has made me more confident regarding mainstream science and how to respond with useful hints (instead of solutions) to homework questions.
12. 5 points

## Bob Lazar

Element 115 (moscovium) has a half life of about half a second, so is not very practical as a target. https://en.wikipedia.org/wiki/Moscovium (And I doubt that element 116 can be produced by firing protons at the nucleus.) "Immediately decays"? It is true that the half life of livermorium is less than that of mosocvium; but it is not immediate. Livermorium decays via alpha decay. In other words, it emits a helium nucleus (a pair of protons and a pair of neutrons bound together). https://en.wikipedia.org/wiki/Livermorium It does not emit anti-protons. That would violate all sorts of conservation laws. https://en.wikipedia.org/wiki/Conservation_law And anyway, what would be the point? This can only be of interest to people who think that antimatter=magic. What are you going to do with these anti-protons? Presumably combine them with some protons to generate energy. But you can't get any more energy out of that than you put in. So the whole process of accelerating some protons, transmuting 115 to 116, then capturing the anti-protons and then generating some protons for them to interact with, then controlling their interaction and directing the energy ... all takes energy. And must run at less than 100% efficiency. https://en.wikipedia.org/wiki/Laws_of_thermodynamics So you are going to get less energy out than just using shooting the original protons out the back of the rocket. Or using the heat from the rapid decay of the moscovium (you will be left with no useful fuel after a few minutes, anyway). There is nothing to critique here. This is just meaningless word-salad from a bad SF book. No references here because there is no such thing as "Gravity-A waves", "Gravity B waves" or "Gravity Amplifiers". Also, gravitational waves (which do exist) are not directly related to gravity. Gravitational attraction is not a wave phenomenon. Also, gravity is only attractive; there is no practical or theoretical reason to think that somehow causing gravitational waves (if that is what the ignorant author means) to interfere would cause any gravitational effect (either pull or push). Gravitational waves cause stress (stretching and shrinking) in directions orthogonal to their direction of travel. This effect is too small to be significant, unless you are a few miles from two merging back holes. https://en.wikipedia.org/wiki/Gravitational_wave Gravity waves are something completely different. They are a phenomenon in fluid dynamics and have nothing to do with gravity (in the sense implied here; they are caused by gravity, not a cause of gravity). https://en.wikipedia.org/wiki/Gravity_wave It is almost as if the author doesn't know what they are talking about. And are just stringing together a bunch of words they don't understand. See anyone can do it.
13. 5 points

## An extension of Quantum Field theory concerning universal expansion

Thank you all for your insightful comments and helpful links, and sorry I didn't reply earlier but I just joined and hit the five reply limit. You've helped me see the flaws in my thinking and weak areas of understanding, especially misunderstanding space/time to have elastic potential energy (as this was just a misunderstanding of how the models are visually represented), not using accepted vernacular, and uniform expansion. In retrospect, I should've just left out the Quantum Field explanation as I'm sure most of you understand more of it than I do already and it's already discussed on these forums. It's all forced me into the frightening conclusion that if my thoughts in this area are to have any value I'm going to have to move from being interested to being dedicated and learn some math. Darn it.
14. 5 points

## How can the cosmos be eternal?

A better question is why $10^{-43}$. Would it help to recognize that number is one unit of Planck time with our current observable universe to the volume of 1 Planck length. The temperature being equivalent to Planck temperature. The Planck units are in essence boundary conditions on which our ability to mathematically describe in essence breaks down into Infinities and nonsensical results. You often only hear the space and time axis in essence flipping roles for the GR descriptive but cosmology must also include both macro and quantum effects. So its good to understand how the limits of the macro and quantum theories apply. (String theory also recognizes these limits) One detail as mentioned in this thread is were describing our Observable portion in essence the limits of shared observable causality with our current universe. Time being a measure of rate of change or duration you in essence need a dimension in order to have something to measure or even something that must be able to change. However one must also realize that the t=0 represents the collective worldlines of all particles in our observable portion extrapolated from the closest we can mathematically describe and potentially measure. In the closest to pointlike we can describe. It does not represent any time outside our region of shared causality. In essence $10^{-43}$ is the origin of time for all potential worldlines in our observable universe that are extrapolated to the beginning of our observable universe (as the emitter event).
15. 5 points

## Space anchor idea

Thank you for all your feedback. I’m currently working on some mental health issues and cannot reply on give the answers the time that I would like to in regards to research and time and I struggle to express the concept fully and accurately, more to come but I have to work on my stability at this time kind regards David Wavish
16. 5 points

## What is dark matter?

As swansont has already stated, dark matter is matter that is hypothesized to exist due to the apparent gravitational effects we see, but which doesn't interact electromagnetically like the regular matter we are used to dealing with. This means it does not emit, reflect, or absorb light either, thus the description "dark". And as he said, we don't really know just what it is made up of yet. There are a couple of possibilities. Massive Compact Halo Objects (MACHOs) would be objects like neutron stars and black holes. These are object formed from "normal" matter (or at least a far as black holes go initially from it), but compact so much mass into a small area that they are just to small and dim to see individually. However, we need quite a bit of dark matter to explain observations, and there are reasons why we don't think the universe could have this much mass in the form of MACHOs, as it would have effected how the universe evolved, resulting in one that looks a bit different from what we see. Another possibility is Weakly Interacting Massive Particles (WIMPs) These are sub-atomic particles that have a rest mass, but just don't interact via the electromagnetic interaction. (And pretty much everything having to do with how we interact with regular matter, from touching it or seeing it, to chemical reactions involves electromagnetic interaction) These "ghost-like" particles would pass right through you like you weren't even there. While this this seems bizarre, we actually already know of a particle that behaves like this, the neutrino; Billions of them pass through you every day with your ever noticing it. Neutrinos ( or at least the type we know of) don't work for dark matter for various reasons, so the WIMPs of dark matter would be something like, but not identical to neutrinos. It is also possible that both of the above play a role in making up the total effect we see. swansont also mentioned attempts to explain things by a modified theory of gravity. The problem with this is that a number of observations are not compatible with such an explanation. An example would be galaxies that appear to be identical but exhibit different gravity profiles. Even if the rule of gravity were different than what we presently think they are, they would still need to be consistent from galaxy to galaxy. So while its perfectly possible for different galaxies to contain different amounts of dark matter and thus as a whole act differently in terms of gravity, it is hard to explain why the actual rules governing gravity would change between galaxies. Having said this, it is still possible for a modified gravity theory to play some role, if combined with dark matter. A new theory of gravity which also incorporates a mix of MACHOs and WIMPs could end up being the final answer. Right now we are at the stage of continuing to make observations in order to narrow the playing field. We have eliminated some possibilities, but there are more to explore.
17. 5 points

## Sorry about the downtime -- we're back!

Fake news! It was a perfect renewal! Absolutely perfect. In a world where even my fridge can give me reminders, I still managed to forget. Luckily Capn was able to social engineer his way through my answering service who sent a page out to me stating "CAPN REFSMMAT - RE: WEBSITE". They even listed a hospital he was calling from 😂. I wasn't on call today so when I heard my answering service text me I about lost my mind until I saw who it was.
18. 4 points

## There's a black hole lurking within 1,000 light years of Earth – and you can see stars circling it with the naked eye

Disclaimer: Black hole not visible, southern hemisphere required. https://www.theregister.com/2020/05/06/nearest_black_hole_earth/
19. 4 points

## Climate Change

My little bother just ate all the Scrabble tiles and his poop made more sense than you do.
20. 4 points

## Small to Large? [Split from What determined the inital state of the universe?]

Why is it apparent that small things determine how big things work and not vice versa? Why is cause and effect noncommutative with respect to "size". In the sense that CAUSE is due to some physical laws: Quantum fluctuations CAUSE real and virtual particles. Real particles cause leptons, quarks, bosons. Leptons and quarks cause protons, neutrons and electrons. Protons neutrons electrons cause hydrogen helium and carbon atoms. Hydrogen, iron and oxygen cause stars, planets, and water. Stars, planets and water cause galaxies, solar systems, and oceans. Galaxies do not cause stars. Stars do not cause hydrogen. Hydrogen does not cause protons. Protons do not cause quarks. Quarks do not cause real particles. Real particles do not cause quantum fluctuations. The direction of time is forwards? The direction of cause is bigwards?
21. 4 points

22. 4 points

## IQ rates are dropping in many developed countries

Citation needed. Maybe it is just compensation for the Flynn effect. I would guess the lack of a good definition of IQ and the corresponding arbitrariness of the tests accounts for a large part of it. Maybe modern communication technology and social media means that cultural change is happening faster and the tests can no longer be fudged quickly enough to compensate.
23. 4 points

## The world has changed...

I think you'd better take a good look around, Dim, and not how you imagine things. You might not like what you see.
24. 4 points

## Element 115 as Flying Saucer Fuel

After 8 seconds it said "This film is not presented as fact." So I did not watch the rest. Correct. I am not interested. But if anyone provides reliable scientific evidence about progress in our understanding of gravity (and/or anti gravity) I would be very interested. Warning: Straw man ahead: *) Replace alien technology with "magic", "psychic powers", "spirits", "life after death". The scientific content would be the same (zero).
25. 4 points

26. 4 points

27. 4 points

## Coronavirus Terrorism

The plot revolves around a group of highly trained professionals who break into homes of elderly folks and aggressively cough into their faces for a few minutes. In a heartwarming twist one of their presumptuous victims confuses the terrorist with their grandchild to whom she had lost contact. After a furious intermezzo consisting of baking and copious amount tea the terrorist realizes that deep inside he is just longing for the love of a family. Meanwhile the grandparent realizes that the nightly visitor in stealth suit is indeed not her grandchild (the climbing hook on the balcony being a crucial hint- as well as a flashback highlight that the real grandchild had a fear of heights). But she enjoys the moment too much to care.Tragically, this human moment is also what ultimately resulted in successful infection. The terrorist becomes guilt-ridden when it becomes clear that the lonely grandma is not long for this world and he tries to reach her a last time to say his farewells. Meanwhile, his terrorist buddies consider him a traitor and try to stop him resulting in a highly choreographed fight scene involving lots of offensive coughing and running noses in slow-mo (the filmmakers did not consult experts as per usual and did not realize that this is not part of the symptoms). Finally, he survives all these ordeals and reaches the grandma, who turns out to be a special CDC/Homeland security agent in disguise (Jason Stratham) who have been delaying a rollout of coronavirus testing in favour of sting operations to catch corona-terrorists. PS: can anyone tell that I really, really do not want to read those student reports?
28. 4 points

## Vaccines and autism

The autism connection has been peer reviewed and the author of that has been discredited and struck off. He, to cut a long story short, had a financial interest in pursuing this position. Unfortunately, this myth has persisted and been magnified by the internet. Google 'andrew wakefield autism'
29. 4 points

## Cleaning Coins With Salt?

What up! I know I am about 16 years late but, I just wanted to point out that (like others have) @Tesseract was incorrect in saying that salt and vinegar makes hydrochloric acid. I dislike the spread of misinformation. Next time make sure something is correct before you post it to the internet. Also I made this account to post this. But I'm sure nobody will ever see this. I put so much time and effort into doing something so utterly pointless.
30. 4 points

## Can someone please explain galaxies moving 5 times light speed and

Your only questions are sarcastic and unhelpful. Your assertions have mostly been wrong, and have been pointed out to you, but you've chosen to ignore them. You're rejecting explanations without reason, simply because they don't seem intuitive to you. This isn't personal, it isn't about you. It's your approach to learning that's causing a problem in discussions. I have to ask, is there any way to reason with you on this subject, or is your incredulity always going to be an impassable obstacle? How can we turn this discussion into a meaningful one? Several people have tried explaining what mainstream science says on this subject, but it's hard to have a conversation with you when half the effort is spent trying to get your fingers out of your ears.
31. 4 points

## Is this war with Iran?

The plane crash involved a Boeing 737-800NG, not the MAX but a previous version with stable aerodynamics and no computer override. The plane was 3 years old and had been in for maintenance on Monday. And Ukraine has suspended all flights into the area, but hasn't grounded similar 737-800NGs. I personally haven't seen it, but there are reports of a video showing the plane coming down engulfed in a fireball, and wreckage photos show puncture damage from either engine failure and breach of blades, or shrapnel. The plane was at 8000 ft when contact was lost and it disappeared from radar, but the ground elevation in the area is over 3000 ft, and it had made a sharp left turn as it climbed out at less than 5000 ft relative to ground elevation. At this point it would have been close to the Malard missile launch site. Given the circumstances, this does not seem to be a technical issue, even if there had been enough time to do an investigation ( usually takes months ), and engine failiures do not result in that type of a crash. I would assume, until evidence proves me wrong,, that the plane was warned not to overfly the missile launch site, but was mistaken by Iranian air defenses as incoming cruise missile or possibly even MANPAD launched in error at a low flying target. I have also seen reports of the 63 Canadians being mostly students from the Toronto area. Seems Iran's 'insignificant' response may have led to some very serious consequences, and the 'fog' of war has shown up again. May all 180 passengers RIP.
32. 4 points

## Can someone please explain galaxies moving 5 times light speed and

It is very disingenuous to ask a question then assert the answers are wrong.
33. 4 points

## my hypothesis: dark matter observations are relative

A clock near a black hole ticks at “1 second per second”, a ruler near a black hole is “one meter per meter” long. A clock on Earth ticks at “1 second per second”, a ruler near Earth is “one meter per meter” long. Locally in their own small enough neighbourhoods, neither observer determines anything special to be happing. As the name already implies, relativistic effects become apparent only when you compare clocks and rulers in different frames - they are relationships between frames, not things in and of themselves that somehow happen to clocks and rulers. No clock will ever tick at anything other than “1 second per second”, and no ruler will ever measure anything other than “1 meter per meter”, within their own local frames. Time does not “slow”, space is not “stretched”, they merely become local concepts. It is crucially important to understand this point. So, in order to determine the geometry of spacetime, you need to either compare clocks and rulers at different events, or (equivalently) observe what happens when they traverse extended regions of spacetime. What you find then is that different observers may disagree on specific measurements of space and time, but they will always agree on how those measurements are related to one another. In other words - all observers agree on the geometry of spacetime. Mathematically speaking, the object that quantifies relevant aspects of the geometry of spacetime (in GR that is the Einstein tensor) is something that all observers agree on, regardless of where and when they are, or how they measure and determine it. The components of the tensor vary as you go from one observer to another, but they vary in such a way that the overall tensor remains the same one - that is the meaning of “covariance”.
34. 4 points

## Anti- science, science deniers and 'alt' science, do they have a growing following

I think there are certain parallels between people believing in conspiracy and religious belief (religion being, from a certain point of view, the ultimate conspiracy) As folks have pointed out from time to time, when people do not use reason to arrive at a position, you will not be able to use reason to talk them out if it. Studies have shown that presenting such people with contrary evidence only tends to harden their resolve.
35. 4 points

## Science is dogma (split from What is the Purpose of Life ?)

As a silent reader not actively involved in this thread, allow me to offer an observation. Your initial post had one or two points in it that are relevant and worthwhile, but unfortunately your tone and general presence here comes across as arrogant and condescending, You made at least one good point (and some not so good ones), but you failed to communicate them in a proper manner. Please take this as constructive criticism, i.e. an opportunity for growth.
36. 4 points

## Dreams causing real injuries?

This might be possible, if I may offer an opinion, for any number of reasons not apparent form the perspective of an 8-9 year old 20 years in retrospect. It's possible that your vivid recollection of what occurred 20 years ago isn't quite what happen. Time alters our memories and can create false ones that merges imagined experiences with those that are real. If your experience was real and you actually sustained "3 deep knife marks", scars of that experience would likely be visible somewhere on your body today, 20 years later, if they were truly as "deep" as you say. However, you've made no mention of such scars, which could suggest that the sleep injury you sustained was likely not as severe as you might have then perceived 20 years ago, which was likely precipitated and enhanced by the persisting fear an 8-9 year old could have experienced after a night of watching "scary movies". 20 years hence, your memory of the experience was embellished by time. Although, there's strong scientific evidence for the psychosomatic connection between mind and body, which can produce real physical injury, I do not believe this was likely your experience as a 9 year old child particularly without evidence of lingering scarification. I hope this helps.
37. 4 points

## Antibiotic resistance. Suggested tactics

Artificial selection is not necessarily quicker than evolution, but using CRISPR Cas9 approaches, it is simple enough to produce antibiotic susceptible strains. Aseptic technique is still the most valuable tool in the prevention of nosocomical infection. Spreading pathogenic bacteria about an OR - drug susceptible or not, would have significant detrimental effects. So a few things 1) Often antibiotic resistance (AR) genes come with negligible costs to the bacteria, so do not suffer from negative selection. 2) They are often encoded on extrachromosomal transposable genetic elements (e.g. plasmids) or like the MecA gene in Staphylococcus aureus can be transferred by viruses - so you cannot prevent the spread of AR genes between your susceptible and resistant strains. 3) AR genes often, through selfish gene mechanisms, get crowded onto plasmids or prophage with other genes that confer a net benefit, such that they can piggyback on the positive selection of other genes to proliferate. 4) Resistance mechanisms like multi-drug efflux pumps, efflux many many other cytoplasmic contaminants, such they provided a benefit to bacteria in a wide array of environments. 5) Over 80% of antibiotics produced in the developed world are used as growth promoters in agriculture, rather than therapeutics. Therefore most of the interaction between bacteria and antibiotics is happening in the broader environment, not in the clinic. 6) Continuing from above, most of your patients present to the clinic having already acquired the resistant infection in the broader environment, so bacteria in the clinic are unlikely to have a positive impact. Dusting yourself with Staph/Klebsiella/Salmonella/Cholera etc, resistant or not is a terrible idea. You would wind up with far higher rates of infection and subsequent morbidity as a result, with a net negative public health outcome.
38. 4 points

## Exponential Challenge - Find x

This is the kind of problem that is more easily solved if you step back before turning the math crank. Look at y = x^2 and y = 16&x. y = X^2 is a parabola that passes through the origin. y = 16^x is an exponential function, and on the positive x side it rises faster than the parabola-- so it is obvious that there will be no solution for x > 0. On the negative side of the graph, 16^x approaches zero asymptotically, and is already 1/16 when x = -1 (while at x = -1 the parabola is at y = 1). Thus, it becomes obvious that the solution must lie in the region -1 < x < 0. I did a quick sketch of the two functions and it was equally obvious the crossing point had to be somewhere close to -0.5, as stated by Studiot. Understanding the shapes of functions makes trial and error, and heavy math, both unnecessary.
39. 4 points

## Math v physics (split from Direction of time)

Physical laws have certain properties, and you can have maths that have the same properties, but you can also have other maths that don't, including abstract mathematics that aren't based on physical things. For example, you can mathematically take apart an orange and rearrange it into two oranges identical to the original. https://en.wikipedia.org/wiki/Banach–Tarski_paradox The maths aren't restricted by the physical law of conservation of mass.
40. 4 points

## Pascal's Wager - Does this make sense?

Apparently, Marcus Aurelius commented on Pascal's wager about 2,000 years ago:
41. 4 points

## Space layers, gravity/expansion flow. Just an idea

I am more than likely wrong on all accounts but the Idea simply made sense to my current understanding. It seems apparent my current understanding is quite misleading. I appreciate your patience with me in your explanations. This stuff is fascinating the hell out of me though. Could you possibly recommend some entry level physics/calculus books I could begin with increasing my understanding of how all this works?
42. 3 points

## The relative worth of scientifc hypotheses and discoveries

Why does scientific inquiry have to have a quantifiable benefit to society, beyond the new knowledge itself? A benefit that you can't know until you've made the discovery? To quote from The West Wing Senator Enlow: If we could only say what benefit this thing has. No one's been able to do that... Professor Milgate:That's because great achievement has no road map. Well, the X-ray's pretty good. So is penicillin. Neither were discovered with a practical objective in mind. I mean, when the electron was discovered in 1897, it was useless. Now we have an entire world run by electronics. Haydn and Mozart never studied the classics. They couldn't - they invented them.
43. 3 points

## Shapiro-Wilk and Bartlett test

If we take Bartlett first, then the purpose of the test is to figure out for several sets of data, and assuming that each set is normal distributed, whether they also have the same variance. If we think about the second table, it is possible that it represents four sets of data, one for each row, each set of data containing three values, for T1, T2 and T3. Or it is (more) possible that the table represents three sets of data, each containing four values. Let us say that it makes sense that the second table represents experiments in which for each of three temperatures T1,T2,T3 there were made four measurements. Then for T1 it means that values 2.42, 2.83, 2.25, 3.02 were measured, for T2 they were 3.05, 2.21, 2.18, 2.35, and for T3 it was 1.95, 2.23, 2.54, 2.56. We can calculate the estimate variances of each of these samples in the standard way, as 1/3 of the difference between the average of the squares minus the square of the averages. I trust that this is familiar to you? Then we have three estimated variances V1, V2, V3, one for each T. We also have to compute the estimate of the common variance V in case they were actually all equal. That will be $$V = 1/(12 - 3) \sum_{i=1,2,3} (4-1)Vi$$, where the 3 means that we have three data sets, the 4 means that we have four data in each set, and 12 is the total number of data in the table. I have not made the computations, since I have no good calculator handy, and I would probably make confusing mistakes, sorry. Finally you have to compute the Bartlett testor itself. First we need the number $$D = (12-3)\log V - \sum_{i=1,2,3} (4-1)\log V_i.$$ We can see from the formula above for V that it would be a pretty good match if all the V1,V2,V3 are the same, because then V would be equal to all of them, and this $$D$$ would be zero. So $$D$$ having a small value is good. To compute the final Bartlett testor we also need to have $$C=1 + (\sum_{i=1,2,3} \frac{1}{4-1} - \frac{1}{12-3})/(3(3-1)).$$ The testor becomes $$B = D/C$$. Now you have to check $$B$$ against a $$\chi^2$$ distribution with 3 - 1 = 2 degrees of freedom. Having typed all of that, maybe it is not as easy as I first thought. But try to compute as many of the numbers as you are able to.
44. 3 points

45. 3 points

## Mathematical Knowledge

I know I am not supposed to get involved as I have already acted as a moderator (but hopefully in a fairly non-contentious way), but I can't resist the need to point out that there are two ways of defining something: 1. In terms of something else (which is, hopefully, simpler) 2. As an axiom (or postulate or "self evident truth" or whatever) in which case the thing is defined as simply being itself. (I believe this is what "Lawbringer" is referring to as a "circular definition".) All definitions must eventually bottom out to (2). I would not call that a circular definition as I think it is useful to distinguish fundamental concepts that cannot be defined in terms of anything else, from the circular definitions which are often the basis of a fallacy (similar to begging the question).
46. 3 points

## The speed of propagation of gravity

To see whether gravity is a force, simply attach an accelerometer to a freely falling test particle. You will find that the instrument reads exactly zero at all times, even though the trajectory of the test particle makes it obvious that it is affected by gravity. And then of course you have other effects, such as gravitational time dilation, that can’t be explained by forces at all. Thus, gravity isn’t adequately described as a mechanical force. It completes the “zoo” of those particles which the Standard Model predicts within the energy ranges that we can probe with current technology. The hypothetical graviton interacts so weakly that it would be extremely difficult to detect it directly. The entire idea of a “graviton” is based on the notion that gravity can be quantised using the usual framework of quantum field theory. It is in fact easy to write down a QFT for gravity - but the problem is that such a QFT is not renormalisable, and exhibits infinities that cannot be removed via any known method. Essentially, the resulting QFT is useless, in that one cannot extract many meaningful physical predictions from it. So evidently, QFT is not the right method to quantise gravity. Based on current knowledge, it would seem that gravity is conceptually different from the other fundamental interactions, and is hence not amenable to the usual quantisation schemes. This puts a huge question mark behind the notion of a “graviton” - treating gravity as the interchange of vector bosons may not be a meaningful concept. But if it is, then it would not be difficult to incorporate it into the Standard Model (you’d just add an appropriate term to the Lagrangian). This is an area of ongoing research.
47. 3 points

## Posting style (split from Climate science was wrong!)

You already started with an emotional guess about the percentage that was already present. I doubt we can reason you away from that view. I'm very leery these days about people with emotional criticisms. The current POTUS is criminally proficient at screaming he's being treated unfairly, and it's gotten him a lot of leeway he didn't earn and doesn't deserve. I'm suspicious that you're setting the stage here by painting people as unreasonable and rude if they argue against you.
48. 3 points

## Does anyone know what the little red piece is on my classroom's life size human skeleton model is?

3. Ran out of white Legos 2. Nose from his Halloween costume 1. Weight Watchers merit pin
49. 3 points

## Sun Black hole

The Sun cannot collapse because of radiation pressure. If nuclear processes in the Sun's center were to stop ( once enough iron accumulates in its center ), there will be a partial collapse to what is termed a white dwarf star. Further collapse is prevented by electron degeneracy pressure ( see the Pauli Exclusion Principle ), and that is how it will spend the remainder of its life. IF our Sun was a couple of times more massive, electron degeneracy could not stop the crush of gravity, and it would collapse even further, until neutron degeneracy would stop the collapse and our ( more massive ) Sun would then become a neutron star. IF our Sun was about ten times more massive, even neutron degeneracy could not stop further collapse. As a matter of fact we don't know of any mechanism that could stop the gravitational collapse of such a massive object. Gravity would squeeze it small enough that our best theories stop making sense , and we can't even investigate/observe because the universe throws up an event horizon around it that prevents any information coming back out.
50. 3 points

## When did science become vast?

If you take any science subject, each field of study shows how the subject relates with regard to how we observe the universe to be. If you want to learn about black holes, starting with the chemistry of fusion shows how stars are formed, and how they can collapse. Physics and the accompanying mathematics will show how gravity is affected by the hyperdensity of the degenerate matter of a black hole, causing severe spacetime curvature. If you want to learn about vampire wasps, studying evolution helps connect the way traits manifest themselves in biological processes, and chemistry helps us understand how those processes function. Studying how agriculture and animal husbandry completely changed the way early humans functioned in groups will lead you to many different fields of study. Geography, biology, physics, chemistry, astronomy, and others all cover parts of the explanation. And the height of the scientific methodology is in using experiment results to predict the results of other experiments. Einstein was able to predict, using previous experimental data, that light would bend when subjected to a strong gravitational field, long before we had a way to test it. Darwin was able to predict the presence of certain animal types based on plants in the environment (a deep spur in a flower requires an animal with a long nose to pollinate it).
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