1

Technology / Re: Does cold weather damage the batteries used in an EV?

« on: 11/01/2025 15:37:15 »

First of all, cold means salt, and especially Tesla hasn't shown any obvious awareness of the need to protect parts from corrosion.  That's an issue since batteries are at the bottom of the car where the salt is.

2.     If a rechargeable battery loses some capacity (in the sense of KWh of electrical energy it can store or deliver)  in the cold weather,  where does that energy go?

Capacity and energy are different things.  Sure, you put X energy into the car, it gets cold, and now there's less energy available. It went away with the heat?  Does the full charge return if it warms up or do you need to top off a full battery if it's been cold and it's warm now?  I don't know the answer to that one.

2

Physics, Astronomy & Cosmology / Re: What Is The Final Parsec Problem ?

« on: 06/01/2025 18:47:47 »

    When galaxies collide, their central supermassive black holes (SMBHs) should also eventually merge.
    However, as the SMBHs approach each other within about a parsec (3.26 light-years), the density of stars and gas in the galactic core becomes too low to effectively remove the energy and momentum needed for the final plunge and merger.
    This "energy loss problem" prevents the black holes from spiraling inward and merging within a reasonable timeframe.

So how do Black Holes merge then ?

The quote you give kind of says it.  To get closer, their kinetic energy must go somewhere, else, like Earth, it just keeps orbiting the sun without getting closer.

Thing is, the way this energy is dissipated is by flinging other matter away, giving that matter the orbital energy of the pair. Once the material is all gone, only new (not orbiting) material can contribute further to this process, and that takes a lot of time.

They will eventually merge, just all all planets will eventually fall into the sun given enough time and no external dissturbance.  Any pair of orbiting objects emits gravitational waves and that energy comes from kinetic energy.. Earth for instance emits GWs at the rate of about 200 watts, and the kinetic energy of Earth will run a pair of 100W light bulbs for an awfully long time.  The sun will swallow Earth before that has time to happen, but that's the fate of say Jupiter.

Likewise, all black hole binaries like the undoctored picture you took will eventually merge, but the universe is only 14 billion years old, nowhere near long enough for gravitational waves to do the job at a full parsec away.


Fun fact: Two sheep circling each other will emit Baaavitational waves.

3

New Theories / Re: How does Hamdani explain the twins paradox?

« on: 26/12/2024 22:28:30 »

What's considered established at some point, may no longer be the case a few decades or even years later.

It doesn't matter who said that. What's important is whether it's true or not.

I completely disagree. It being true is a fairly trivial thing, but the fact that the new established theory has, without exception, only been made by those who first understood the previous established theory, means that no troll (somebody proposing anything with said understanding) has ever contributed to progress, and that was the point of the comment.  Not saying that you're a troll, but I am noticing that you use arguments that seem only used by trolls, notably the first quote above.

What's more important is whether the equations accurately represent physical reality.

The twins scenario is not representative of physical reality. The exercise is a simplified exercise in Minkowskian spacetime, and real spacetime is Minkowskian only locally. The twins scenario is not a local scenario.
This means that you need to use GR to represent non-local physical reality. The SR exercise (especially your funny diamond one) is inapplicable since the answers it gives are trivial differences compared to the differences GR would produce.

You seem to think that you know better than professional scientists working in this field, including Einstein.

The average professional scientist knows next to nothing about relativity, but their field of expertise is elsewhere. No, I never claimed to know relativity better than any student that say took a graduate level course in it. I know it well enough for my purposes, which doesn't involve actually getting a rocket to go where I want it to.

Einstein reportedly said that he "didn't recognize" his theory of special relativity anymore because of how its interpretations and applications evolved far beyond his original formulation. When he developed the theory in 1905, his focus was on solving specific physical problems, such as reconciling Maxwell's equations of electromagnetism with the principle of relativity.

However, as the theory gained widespread acceptance, it became a foundational framework for theoretical physics and was interpreted in ways Einstein had not anticipated, especially in the hands of other physicists. For instance:

1. Mathematical Formalism: Mathematicians and physicists like Hermann Minkowski reformulated special relativity in a four-dimensional spacetime framework. While this interpretation became standard, Einstein initially resisted Minkowski's geometrical approach, as it was different from his more intuitive understanding of the theory.

This is a fairly accurate response by chatgpt.  I didn't keep the entire quote. Minkowski reinterpreted his 1905 theory as spacetime geometry, not the way Einstein interpreted it in his paper. Without this new interpretation, he'd not have been abble to finish the theory (GR).  Yes, he didn't recognize it at first, but he needed to recognize it to make progress. Minkowski (his mentor) did him an extreme favor by doing this. Minkowski was given too little credit for relativity theory.  Einstein published it first, but did not do it on his own.  He had to learn a lot of mathematics along the way.

#369: time dilation is a coordinate phenomenon, differential ageing is a real world effect.

This is a super important distinction.  A physical fact cannot be explained as a function of  mental abstractions.  Time dilation is a coordinate effect. Coordinate systems are mental abstractions, and no amount of mental imaginations are going to change what physically goes on.

This diagram from Wikipedia is supposed to be the established explanation for twin paradox.

The wiki article mentions perhaps half a dozen ways to explain the twins thing, many of which are abstract.

The wiki article is a very good resource, but most of its text concerns coordinate effect (things that are true in one frame and not in others).  This includes any mention of simultaneity, distances, durations, and any numbers (coordinates) assigned to points.
Physical facts include Differential aging and any event, and also spacetime intervals.  These things are frame invariant and observer independent and are not abstractions. The twins scenario is about physical differential aging, and saying any physical fact is caused by human mental abstraction, is idealism at best, similar to saying the apple ceases to exist when not being perceived.. As I said, the wiki article is very good, and it never asserts anything like that.

The picture you reference is one of the abstractions. It shows lines of simultaneity, and simultaneity is completely abstract, having no physical meaning. That doesn't make the picture wrong, but it isn't a physical explanation.

It predicts apparent time jump in the observation by traveling twin

No it doesn't.  In fact, it doesn't mention observation at all since there are no light lines in the picture. If the twin looks at Earth when turning around, he sees the same thing just before and just after the acceleration. The observation only changes in redshift, but no time jump is observed.  What is observed would be physical fact, and nobody regardless of where they are could contest it.

Point is, learn what the diagram actually shows. It shows an abstraction, something any person anywhere at any time could compute.  All one needs to observe is an itinerary. No other observation need be made at all by anybody.  Nobody observes a time jump. The jump is just a result of a change in arbitrary selection of inertial frame, and the Lorentz transformation details such changes.  The Lorentz transform is once again purely an abstraction.

to also accept reverse time jump or rewind when the direction of the acceleration is away from the observed twin.

Yes, but again, this 'jump' is an abstraction, not anything that physically happens. One is always free to jump back and forth between two different reference frames. Acceleration isn't required at all to do it, and doing so makes zero physical difference to the universe.

    "Reverse Time Jump" --->  It sounds like you're describing something amazing, maybe time travel into the past.

Yes, it sounds kind of amazing when a coordinate effect is presented as a physical one, and this is indeed the gist of the Andromeda scenario. It's just an abstraction with no physical effect, no actual acceleration required, and no observation of any time 'jump' in either direction.

4

New Theories / Re: How does Hamdani explain the twins paradox?

« on: 21/12/2024 14:26:36 »

What's considered established at some point, may no longer be the case a few decades or even years later.

All the trolls say this. If you don't want to be branded a troll, it probably isn't a good idea to quote their handbook.

Turns out that nobody ever overturned established theory (however wrong) by not first understanding the established theory. I defy you to find a single exception to that.
Nobody overturned established theory by entering "Einstein wrong" as their search criteria, which is one way to find denialist videos.

Chatbots are also known to be consistently wrong when it comes to questions with so much misinformation in the training materials.

What does it show when they are not co-located?

Differential aging is inapplicable to clocks that are not co-located. This is basic relativity of simultaneity, something you seem not to understand if you ask a question like that.

If the acceleration is done in circular manner, say 1 light second in circumference, while the twins travel at c/2, then to turn the direction by 90 degrees takes half second, while turning the direction by 180 degrees takes one second by maintaining their speed. Alternatively, if the second twin is only given half second to turn, he must turn around with smaller circle, thus higher centripetal acceleration.

Cool. I take it these distances and speeds are as measured in the Earth frame. Speed maintained throughout, but one takes half a second longer to get to the new course heading.  A couple fine details are missing, but assuming these turns are executed at exactly 90 or 180 degrees, there will indeed be differential aging when they meet at the end. Can you compute it? It's fairly trivial.  Which will be older, and by how much?  Most importantly, what do you think the example demonstrates?

If you can't compute this most basic thing, then what was the point of bringing it all up?

5

New Theories / Re: In four dimensions, must an object move at c in at least one of them?

« on: 11/12/2024 17:16:13 »

Two people pass each other on the street; and according to one of the two people

This is a nit, I know, but this sort of language has set public understanding of modern science back by decades since the wording seems to suggests that physical reality is dependent on human observation, which is true of neither relativity nor quantum mechanics. That rant said, keep in mind that "according to one of the two people" is a misleading shorthand for "relative to the inertial frame in which one of the two people is stationary".

Humans choose different frames all the time, and not often that one except when checking one's pockets or something.

Secondly, another nit is that using special relativity presumes flat spacetime, and the spacetime between here and Andromeda is not flat.  I'm also willing to ignore that since it is besides the point being illustrated by the example.

an Andromedean space fleet has already set off on its journey,

Third nit is that this statement is a counterfactual, a statement of the state of something unmeasured. Such assumptions are typically assumed in special relativity exercises, but not in quantum mechanics where few consider the principle to be sound.  I am fine with this assumption for this exercise.

None of these nits are fatal to the point, or make it wrong.  Yet.

How can there still be some uncertainty as to the outcome of that decision?

Exactly because it has not been measured. That leaves it uncertain to the measurer, and in fact it will never be measured because by the time the light gets here, the telescopes will long since have ceased to function.

But Penrose assumes both a 3D spatial universe (presentism) and a 4D spacetime universe, and the paradox seems to revolve around these two incompatible models being used at the same time.
In the 4D block model, the entire history of the universe has the same ontology, meaning the invasion is objective fact and is not in any way a function of a reference frame. Presentism is not compatible with relativity of simultaneity. Simultaneity across the universe is objective and not observer or frame dependent. He needs to pick one model and stick with it. This is more than just a nit. It crosses the line into being self-inconsistent.

If to either person the decision has already been made, then surely there cannot be any uncertainty.

Under the block model, all events have equal ontology and the decision very much is part of it. The only thing that the two observers are doing is comparing different pairs of objective events. There is no 'has already been' of anything since that is a reference to the present.

according to one of them, the decision lay in the uncertain future, while to the other, it lay in the certain past.

Here is a blatant reference to presentism, something totally incompatible with the 4D spacetime model his two people are leveraging. Thus Penrose sows the seeds of confusion rather than adding clarification to what SR actually says. Bad form...

So many many light years away, the "paradox" of Andromedeans having launched, or who will launch, a fleet, is well beyond an observational limit.

The observational limit is one's past light cone, and that cone is identical for both observers (well, a couple meters apart actually), but way over at Andromeda, those two different light cones are still only a couple meters apart.


A more correct wording of the Andromeda scenario is that we have these two different inertial frames differing by a couple m/sec in velocity, and we have one event of these two people passing by each other, and another event of the Andromedan fleet launching. Relative to one of those frames, the people passing event occurs first, and relative to the other frame, the fleet launch event occurs first.  Same two events, but ordered differently in one frame as compared to the other. That is a far better wording of the scenario that presumes SR and it utilizes only B-series language.

6

Just Chat! / Re: Help!

« on: 10/12/2024 16:10:06 »

I tried to reply to Hamdani on his "origin of the magnetic field" and it came up as a new topic which I find I cannot delete. Any suggestions?

I fixed it. Not deleted. It is now a reply to that topic.
As for why it occurred, no idea.  Wrong button pushed?  The topic title was different ("field" instead of "force"), so that means it was never composed as a reply in the first place, and suggests the post wasn't opened via the 'quote selected' option.

7

Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 07/12/2024 18:53:02 »

I was hoping we could lean towards what an exact reason for the different ages of twins is.

Am I missing something? I was of the opinion that this question was comprehensively answered at an early stage in this query.

That was indeed done in the very first reply, the important part being this:

There are many ways to explain the difference, so there is no one correct way.

That means that anything claiming or asking for 'the correct way' is already presuming something wrong.

The rest of the post lists only one of the ways to explain it, and also provides counterexamples to every one of the 'explanations' mentioned in the videos, both of which were shown to be mistaken in subsequent posts. Takeaway is to use a peer reviewed text to get your information, not pop videos, even those put out by supposedly knowledgeable celebrities.  An arm-chair amateur like me should not so easily be able to find the mistakes in them.

If you want another explanation, it can be something as simple as "That's the nature of Minkowskian geometry". A straight (timelike) path between two spacetime points (events) is longer in length than one that isn't straight. This is unintuitive since in Euclidean geometry, the opposite is true.

8

Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 06/12/2024 15:25:33 »

"Einstein based special relativity on the idea that the speed of light is the same for all observers.

That it is the same relative to any inertial frame. It is not true relative to non-inertial frames, and there is no mention of observers in the premises.

That's because a space-time distance that is zero for one observer is zero for all observers.

It's called an interval, not a distance, and any interval (zero or otherwise) between two events or along any worldline is frame independent. Again, observers play no role in this.

So this speed, c, is an invariant speed.

You make it sound like frame invariant light speed is derived from this zero interval, rather than the frame invariant interval (of any value) being derived from the fixed light speed postulate.

You then only move into the time-like direction, and in this direction, you move with the speed of light.

That's like saying that a school bus is parked in my driveway (our reference frame), front bumper against my garage door. 20 ns later the rear bumper is 10 meters away at the street?  Did the bus move at faster than c? No. It's just a different part of an extended object and the thing isn't moving at all. Likewise, you are a worldline, an extended object that is present at both events delimiting the measurement. You don't move from one event to the other, it's just different parts of you that are present at each event, just like the bumpers being different parts of one bus. It isn't motion.

All that said, yes, different definitions are used, and it is commonplace to express motion through spacetime as taking place at c, expressed as a four-velocity, not a normal velocity.

9

Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 29/11/2024 00:26:06 »

. Having never used supposed "AI"(no intention of doing so-you can't teach an old dog new tricks!), I am in a weak position to criticise. I have seen some atrocious rubbish in replies to questions posed by others and a high degree of suggestibility. In response to a question that requires a blunt "NO", answers will often digress into unsubstantiated speculation with the seeming aim of perpetuating the discourse rather than delivering a straightforward answer.

This is very perceptive.  Yes, the answers always seem agreeable, and if you protest a correct answer by asserting your own sufficiently plausible rubbish, none of the LLMs seem capable of telling you that it's still rubbish. It might seem a bit skeptical, but it will encourage you to explore your line of thinking rather than point out where it contradicts evidence or contradicts itself.

I didn't want to tell copilot that its answers were rubbish. I had hoped that it would figure it out itself after I pointed out inconsistencies in its replies.

We may not need forum moderators in the future, an LLM can analyse and critque the work produced by the forum users LLM well enough.

Moderators are needed to moderate, to recognize and deal with posts not complying with the rules. Being correct is more of a job for site experts, be they moderators or not.
I'm no expert in pretty much any subject, but I know enough to take apart a lot of answers I see from AI.

(I copied and pasted the reply @Halc obtained from Gemini).....   

Actually, Hamdani provided replies from both chatGPT and gemini. I just copied his quotes so I could color them

My replies below are replies to chatGPT apparently agreeing with much of what gemini had to say..

You say that "spacetime is curved due to the acceleration" in an accelerated frame..... It would be better to mention that acceleration causes the perception of curvature, or locally mimics gravitational effects due to the equivalence principle.

But that isn't right. There is no curvature locally, so there cannot be any local perception of it. In the non-local case, most of the effects are due to the accelerated frame. it is quite hard to distinguish curved spacetime from flat since all the effects are present in both, but differently.
For instance, I am under proper acceleration of 1g and dangle a clock on a long rope. In both cases the clock on the rope will run objectively slower, so that effect is not due to curved spacetime. But the two cases differ a bit for how much slower since they differ. Nearby, it differs but a little, but for a gravitational field of a small mass, it can differ a lot over not that much distance.

The equivalence principle does not suggest any of this

In an accelerating reference frame, spacetime itself doesn?t curve in the same way...

It doesn't curve at all. Spacetime curvature is objective, not a coordinate effect, and an accelerated frame is just a coordinate choice. I would have immediately grilled gemini on this point, but I have no access to it.

students using LLM to write the essays and someone else using a LLM to mark and grade them.

They get what they deserve if they commit the same sins. Education should devolve into GIGO. Nobody should pay for any pseudo-education implemented in this manner.


I talked to my AI about black holes and got Newtonian answers in response. It had no clue.
Thought of another one: Sagnac effect is a favorite empirical disproof of anything Einstein.  Let me have a go:


Does light travel west faster than it does east?

Light travels at a constant speed in a vacuum, ... This speed remains the same regardless of the direction in which the light is traveling, be it west, east, or any other direction.

The notion that light could travel faster in one direction over another doesn't hold up according to our current understanding of physics. The speed of light is influenced by the medium through which it travels (such as air, water, or glass), but not by the direction.

So if I create a vacuum tunnel and some mirrors around the world and shine a pulse in both directions, both pulses will return to the origin spot at the same time?

Yes, exactly! In your vacuum tunnel setup, if you shine a pulse of light in both the west and east directions simultaneously, both pulses would return to the origin at the same time. The speed of light in a vacuum is constant and does not depend on the direction of travel.

This constancy of the speed of light is a cornerstone of Einstein's theory of relativity and is true regardless of the motion of the source or the observer. It?s one of the fascinating and sometimes counterintuitive aspects of the way our universe works.

So the Sagnac effect disproves relativity then? It predicts that west and east light go different speeds and measurement of this difference is used to detect absolute rotation. Sure, most Sagnac devices have a far smaller circumference than a planet, but the principle is the same

...The Sagnac effect occurs in rotating reference frames, such as a rotating disk or the surface of a spinning planet like Earth. In these scenarios, if you send two beams of light in opposite directions around a loop, they will take different amounts of time to complete the loop.

So the two pulses do take different times to come back to the emitter then?

Yes, in the context of the Sagnac effect within a rotating reference frame, the two pulses of light would indeed take different amounts of time to return to the emitter.

Not in the context of Sagnac. In the context of what actually happens

Let's break this down in the context of what actually happens with light pulses and rotation.

If you set up a vacuum tunnel with mirrors and shine a pulse of light in both the westward and eastward directions, the two pulses would indeed take different amounts of time to return to the origin if the system is rotating.

So I didn't color anything, but it didn't take much to get it to contradict itself. The LLM did not take into account the rotating frame of reference in the first reply because despite the real-Earth scenario, I didn't word the question in a way that drew attention to the fact that we're working with a rotating frame, despite the fact that west and east are not even defined on a planet that doesn't rotate.

I did word the one query as an attempt to discredit relativity like so much training material attempts to do, and it at least didn't take that bait. I partly wanted to see if I could lead it down a false path if it looked like it was my purpose to do so.

The copilot replies were edited heavily, cutting it down to actual replies, and cutting out all the educational stuff it tried to add on, and of course all the congratulatory stuff at the end about how perceptive my questions are. It tacks that on to ever single reply in some form or other.

10

Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 27/11/2024 19:09:27 »

Asking chatbots about relativity is almost always going to get wrong answers.
I can highlight the wrong and particularly correct and really wrong answers.

Is GR needed for accelerated frames of reference?

Yes, General Relativity (GR) is necessary when dealing with accelerated frames of reference, especially when the acceleration is significant or when gravitational effects are involved. While Special Relativity (SR) handles inertial frames (non-accelerating), GR extends the theory to include non-inertial frames, such as those that are accelerating or influenced by gravity.

In GR, gravity is not seen as a force but rather as the curvature of spacetime, and this curvature affects how objects move, including those in accelerated reference frames.  So, for understanding the full effects of acceleration, particularly in the presence of strong gravitational fields, GR is required.

ChatGPT tries to sneak in gravity since yes, GR is needed to deal with gravity. But acceleration does not produce gravity at it implies. It seems to just repeat this comment a number of times.


At least ChatGPT doesn't attempt to leverage the equivalence principle, which I cannot say for the other examples.  Gemini is definitely the worst of the bunch.

The same question for Gemini,

Yes, General Relativity (GR) is crucial for understanding accelerated frames of reference. Here's why:
 * Equivalence Principle: GR postulates that gravity and acceleration are equivalent. This means that an observer in a uniformly accelerating spaceship cannot distinguish between the force of acceleration and the force of gravity. This principle forms the foundation of GR.
 * Curvature of Spacetime: In GR, gravity is described as a curvature of spacetime. This curvature is caused by the presence of mass or energy. In an accelerated frame of reference the spacetime is curved due to the acceleration.
 * Time Dilation and Length Contraction: GR predicts that time runs slower in a gravitational field or an accelerated frame of reference. This is known as gravitational time dilation. Additionally, objects appear shorter in the direction of motion in an accelerated frame, a phenomenon called length contraction.
 * Global Positioning System (GPS): GR is essential for the accurate functioning of GPS satellites. The satellites are moving at high speeds and are at a different gravitational potential compared to Earth's surface. Without accounting for GR, the GPS system would be significantly inaccurate.
In summary, GR provides a comprehensive framework for understanding the physics of accelerated frames of reference. It is a fundamental theory that has been experimentally verified and is essential for many modern technologies.

That was horrible. I would love to have questioned Gemini after that comment and show how it directly contradicts itself.  I tried to do it with copilot, getting this conversation, not as bad as the two above. This is actually my first intentional interaction with any LLM ever.

Is GR needed for accelerated frames of reference?

In some ways, yes. Accelerated frames of reference are closely tied to the principles of General Relativity (GR). Unlike Special Relativity, which deals with constant velocities and inertial frames, General Relativity accounts for acceleration and gravity.

Einstein's theory of General Relativity generalizes the idea of relativity to include non-inertial (accelerated) frames of reference. It essentially states that the presence of mass and energy curves spacetime, which in turn affects the motion of objects. In this context, acceleration can be considered equivalent to gravitational effects?a principle known as the equivalence principle.

So, while you might not need all the complexities of GR for simple cases of acceleration, understanding the full implications of accelerated frames and gravityindeed requires the framework provided by General Relativity. If you're diving deeper into areas like gravitational waves, black holes, or cosmology, GR becomes essential.

Try as I might, I cannot get copilot to mention accelerated frames without dragging gravity into it as well, making the comments ambiguous.

But there is no curve spacetime under special relativity. Are you saying that acceleration creates spacetime curvature?

You're correct that Special Relativity (SR) doesn't involve curved spacetime. SR deals with inertial frames of reference?those moving at constant speeds relative to each other?and doesn?t account for acceleration or gravitational effects.

Note the evasion of actually answering the question.

In General Relativity (GR), however, acceleration and gravity are indeed linked to the curvature of spacetime. The equivalence principle in GR states that locally (in a small region of spacetime), the effects of acceleration are indistinguishable from the effects of gravity. This means that in an accelerated frame of reference, the spacetime can be thought of as curved. So, yes, acceleration is related to spacetime curvature in the context of GR.

Think of it this way: in an accelerating elevator, you feel a force pushing you down, similar to gravity. GR explains this by suggesting that the acceleration causes a curvature in spacetime, akin to how a massive object like Earth curves spacetime, creating what we perceive as gravity.

What do you mean by acceleration being linked to curved spacetime? Does it curve spacetime or not? The equivalence principle indeed says that locally, the effects of acceleration are indistinguishable from gravity, but locally, spacetime is not curved, gravity or otherwise. You seem to imply otherwise when saying "This means that in an accelerated frame of reference, the spacetime can be thought of as curved" when the opposite is true, that locally, even under gravity, spacetime can be thought of (and is) flat.

You bring up an excellent point. You're right?locally, spacetime is considered flat, even in the presence of gravity. Let's clear up the confusion.

The equivalence principle states that within a sufficiently small region of spacetime, the effects of acceleration are indistinguishable from the effects of gravity. In this local sense, spacetime can be approximated as flat, which aligns with your statement that locally spacetime is not curved.

To clarify: acceleration itself does not directly cause spacetime curvature. Instead, in GR, acceleration and gravity are related through the equivalence principle. When we consider larger scales or longer durations, gravity (or the presence of mass and energy) causes spacetime to curve. This curvature affects how objects move, leading to what we perceive as gravitational effects.

So, while an accelerated frame of reference might feel similar to experiencing gravity, this does not imply that acceleration curves spacetime in the same way mass and energy do. Locally, spacetime remains flat, and the equivalence principle helps us understand why the effects of acceleration can mimic gravitational effects in small regions.

There was more, but you get the idea

11

Physics, Astronomy & Cosmology / Re: Has anyone heard of tresino theory?

« on: 14/11/2024 21:57:16 »

A tresino is apparently quite stable, and its discovery (a 5th phase of matter, one beyond the 4th:plasma) seems to have implications on all sorts of things unexplained until now, including why the corona of a star gets so much (100's of times) hotter that the surface of the star, and why planets take so long to cool down.

I don't see how a particle can be a phase of matter at all, but apparently this 5th phase involves some proportion of tresinos, like plasma involves nuclei stripped of their electrons, thus destroying their identity as 'atoms'.

It is theorized that tresinos were a common state of matter early in the universe, but no 'very' early since it took many epochs for things like protons to form in the first place.

Apparently cold fusion, not understood well at first, may finally be explained by properties of the tresino. It isn't fusion, but it may still well be a viable energy source. Much to learn first.

12

Physics, Astronomy & Cosmology / Re: Is it Just Hadrons that The Large Hadron Collider...collides ?

« on: 29/10/2024 19:27:09 »

What is so special about Hadrons ?

They're made of smaller things.

Are there other particles on the menu to be collided too ?

For the most part, no. Electrons for instance are not thus accelerated, although it seems capable of it.

How do they store the particles ?....are they kept in a test tube or something ?

Everything is made of them, so it is simply a matter of isolating them (from Hydrogen say) and then sending em down the pipe.

How many particles are fired at one time ?

Hundreds of billions (of protons, which are hadrons) per beam, and multiple beams.  I've heard a thousand times that figure, so not sure if there are thousands of beams or they can make some beams more dense.

13

Physics, Astronomy & Cosmology / Re: Are Atoms Perpetual Motion Machines ?

« on: 29/10/2024 18:12:28 »

Where does the energy come from ?

It was always there since the atom was made.

2: Does this make atoms (et al) Perpetual Motion Machines ?

No. A PMM is something from which indefinite work can be extracted, at however small a rate. One cannot extract indefinite energy from the motion of an atom.

14

Physiology & Medicine / Re: What Happens To White Cells After They Have Dealt With An Infection ?

« on: 29/10/2024 17:15:32 »

Blood cells (of any type) are fairly short lived, so the white cell counts go down by attrition and lack of many more being produced after their need is gone.  The counts return to normal levels around 5-25 days after infection is cleared, depending on the sort of infection involved.

Red cells might live 4 months. White cells have a life expectancy of only a few days, so if you stop making them in abnormal quantities, their numbers quickly decrease to normal levels.

I have given a unit of red blood cells, and that has the longest wait time before I'm allowed to donate again. Giving whole blood, plasma, platelets, all have shorter wait times.
I've not heard of giving white cells, but I know that early in the covid days before the vaccines came out, whole blood from a person who had recently gotten over a covid infection was in serious demand to serve as a treatment for the more dire cases.

15

Just Chat! / Re: What is the purpose of the conductor in an orchestra?

« on: 28/10/2024 13:31:59 »

but the principal job of a non-playing conductor is to moderate the balance between sections more subtly than the dim and cresc markings on the score, and to add interest by varying the tempo and accent.

Not during performance I hope. This moderation (interpretation of the composer's dream) is done at rehearsal and hopefully not significantly changed in performance. There is also something to be said about changing it up when something is performed night after night, as opposed to school performances that tend to occur 1-3 times at best.


And Alan, love the anecdotes.

16

Just Chat! / Re: What is the purpose of the conductor in an orchestra?

« on: 28/10/2024 13:29:24 »

To be honest, if our conductor made an impromptu change in something just on the night when a piece was being performed, then a lot of us would have missed it and played the thing as we did in rehearsals anyway.

It would seem terrible if any alteration was made without rehearsal. Yes, it's during rehearsal that he's most needed, but also most ignored because until the music is more familiar, concentration is mostly on the paper and less on the peripherally visible conductor..

We had a school band piece where you play the first half, then the 2nd which starts with one of those attacks after a long pause between the halves, then the first again exactly the same. In concert (a competition), our conductor was quite nervous and got to the end of the first half and mistaken thought he had finished, putting the baton down. We're all waiting for the attack signal. Of maybe 80 of us, I think I heard two small toots. The rest of us were watching and very confused. The band leader picked up on our distress immediately and resumed, but it wasn't supposed to go that way.

17

Just Chat! / Re: What is the purpose of the conductor in an orchestra?

« on: 28/10/2024 13:21:50 »

Halc, I am going to dispute, most likely out of ignorance!, something you said. You suggested that after a long pause or a sustained note it is entirely not clear when the attack of the next note is supposed to be. Surely if one has a good sense of time(something I lack) coupled with the sheet music, one has a pretty good idea?

They've practiced, so yes, but a pretty good idea doesn't get everyone on the attack simultaneously, and there's no beat to follow through say a fermata.

In a choir, our was small enough to lack a conductor, so heads turned to the organist and head nods. You get this piece with a loud long final note that needs an abrupt cutoff. All of us are looking at the organist (well to the side, hard to see from the rear, or down in a pit, invisible to the audience) for the head nod. It sounds terrible if the voices don't cut off as one.

18

Just Chat! / Re: What is the purpose of the conductor in an orchestra?

« on: 27/10/2024 17:53:22 »

It's to keep everybody in sync. If you're in one corner of the band/orchestra, you might not be able to hear all the others, and one group can get devastatingly out of sync with others. We ran into this marching in Mexico city, 6 wide down a 2 lane road. A car was parked, blocking one lane, forcing 3 columns to go and the other three to follow. This spit the drums and made it so those in the rear could not see the conductor (the drum major up front with the super tall stick).  We got measures out of sync and it was a disaster. Those who heard both sides just stopped playing.

Anyway, imagine a classical piece with a dramatic pause or long held note. It is entirely not clear when the attack of the next note is supposed to be. The conductor makes this explicit, and everybody should be watching for it.

Small groups (jazz ensembles, barbershop quartet, etc) don't need one, but usually one of the players visible to all uses head/instrument motion to fill the role.

19

Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 17/10/2024 17:00:23 »

I had been told years ago by a theoretical physicist(who now holds a distinguished position at an American university but who will remain nameless) that GR was needed for accelerated frames of reference.

That's actually pretty sad for somebody claiming those credentials.  I googled "is GR needed for accelerated reference frames" and got correct replies from several sources with poorer credentials, but one from a university site.

AI overview: "No, general relativity (GR) is not required for accelerated reference frames:

    Special relativity (SR) is sufficient
    SR can handle accelerated frames and objects, and is sufficient to explain the Twin Paradox. SR is valid in the presence of accelerations because it describes flat Minkowski spacetime"

That is a very poor reference (as is any LLM), but it's correct.  The twin paradox bit is barely relevant since discussion of it is rarely described via changing accelerated reference frames.  That quote seems to answer more "Is GR needed to describe acceleration" rather than to describe accelerated frames, but accelerating objects are perfectly well described in inertial, accelerating, expanding, rotating, and other kinds of frames.

The next hit is better, from University of California, Riverside
"It's a common misconception that special relativity cannot handle accelerating objects or accelerating reference frames. Sometimes it's claimed that general relativity is required for these situations, the reason being given that special relativity only applies to inertial frames. This is not true."

I got no immediate hits that said that GR was required, but I'm sure they're out there. Bottom line is, GR is needed for curved spacetime, which only comes into play with gravity and dark energy, and none of the discussion here has been about those things.  I do not know my GR well enough to say do the tensor calculus required to generate numeric answers. Tensor mathematics is not required for anything in SR, including Rindler frames.

"What is the exact cause of the time dilation of the twin?"
The same thing that causes time.
And I'm not sure we actually know what that is.

I don't think time is something that is caused.  It is exactly like asking what causes distance, which seems to be an ill-posed question.  I do agree that most of the recent discussion has digressed from the immediate topic title, but since it is mostly framed as questions about relativity and not assertions of speculations, I've not moved any of it to the lighter side.

20

Physics, Astronomy & Cosmology / Re: What is the exact cause of the time dilation of the twin?

« on: 17/10/2024 14:10:29 »

Is the bold statement backed up by experimental evidence?

I don't think they've ever made a set of gears with a 1000-1 size ratio, let alone turn any reasonably rigid object at significant relativistic speeds.  The bolded statement  is backed by the very simple mathematics of γ=1/√(1-v²) which is identical on both sides since the sole variable v is identical on both sides.

If an identical measuring tape is glued to the ship, will the earth observer see two of those tick marks go by every second?

The situation is not symmetrical since the ship is accelerating and the Earth is not.  Earth can have a tape measure of indefinite length attached to it, one that the ship can read forever.  The ship (at proper acceleration of 1G) can trail not even a light year of tape behind it.  The tape cannot extend beyond the ship's event horizon without breaking.

How many ticks per second the Earth observer sees depends on when he looks.  At some point, the ticks go by infinitely fast just before the tape ends, and then they see no more.
There was that ship event where the ship guy sees 2 ticks/sec go by.  In Earth frame, the event there that is simultaneous with that ship event, the tape will already have been exhausted.

I made the mistake of trying to apply SR to a scenario where some of the frames of reference were not inertial and were thus in need of GR for solution.

GR is only needed for situations involving gravity (which I suppose my black hole mention does).  But the accelerating frame of the ship is a straight SR exercise.  You might want to look up Rindler frame or Rindler coordinates for info on how SR treats an accelerating frame like this.

SR handles accelerating frames just fine, as it does rotating frames. It handles normal expanding frames as well, but not accelerating expansion frames which involves dark energy and puts things into GR territory.