1

General Science / Re: What would the kinetic energy of a bullet falling from 2Km be?

« on: Yesterday at 17:04:35 »

The terminal speed of a 9 mm bullet is around 250 ft/sec. This is considerably less than the muzzle velocity of an AK47 (1000 - 1500 ft/sec) but dangerous if not always lethal.

2

The Environment / Re: How are global warming and world population expansion linked?

« on: Yesterday at 09:38:56 »

The disgrace of Syria is nothing to do with housing shortage but decades of corrupt government and religion. Governments don't build houses (except in communist countries) but, for the most part, merely facilitate speculative building.

Every country needs fewer people.

But those countries where the population exceeds any possibility of a comfortable and sustainable life tend to be those with the least per capita carbon footprint. So if you are a Believer, you can't blame overpopulation for climate  change.

Believer or not, it is nevertheless apparent that where it results in famine, climate change defines overpopulation.

Climate change is inevitable and to some extent predictable, so the sensible thing to do is to adjust the human population to a sustainable  density everywhere.

3

Just Chat! / Re: Help!

« on: 10/12/2024 19:33:59 »

If you are replying to the last post in a topic, have you tried using "quick reply" at the bottom of the topic page?  No requirement for a title.

4

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.

5

Just Chat! / Re: Theories to start a new world.

« on: 08/12/2024 15:11:02 »

Hi.

   That's a nice reply and can have the best answer award.

And of course the learning of new facts and understandings.

    I'm sure you're smart enough to realise that not everything in the forum is the gospel truth.

Best Wishes.

6

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.

7

Question of the Week / Re: QotW - 24.12.12 - Is there any way to harness nuclear energy other than steam?

« on: 06/12/2024 20:12:35 »

There are already some promising semiconductor thermocouples with > 20% efficiency, apparently.

8

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

« on: 05/12/2024 22:17:16 »

Hi.

"c" has units of m/s and time has units of s, how can one have a speed(m/s) in a dimension of s?

    If you skip all the details, as is often done in PopSci,  it's summarised like this:

If you use a conversion factor c to convert the proper time elapsed to a space equivalent, then.....

   A more rigorous mathematical formulation would require us to be careful about defining 4-vectors and not simply treat them as if they are just ordinary Newtonian 3-velocties with a 4th time-like component strapped on.   For example, we would specify an objects position 4-vector as   (ct, x, y, z)   rather than (t, x, y, z).   That decision alone means that the time co-ordinate for an objects 4-position has units of  metres not seconds.  Next, we would also define the velocity 4-vectors  as a derivative w.r.t. proper time,  d/dτ  of the 4-position vector,   instead of using co-ordinate time t as in newtonian mechanics where the 3-velocity is just d/dt of the Newtonian position 3-vector.  [Reference:   https://en.wikipedia.org/wiki/Four-vector#Fundamental_four-vectors ]
    Note that the last decision makes very little difference at low speeds,   the proper time elapsed for an object is almost exactly the same as the co-ordinate time elpased.   So, it's not too criminal to allow a reader to imagine that a 4-velocity has 3 spatial components which are just the ordinary Newtonian 3-velocity with a 4th component, a velocity in the time direction, strapped on as an extra.   In truth the 3 spatial components of the 4-velocity are not quite the same as the Newtonian 3-velocity and that will become more apparent at higher speeds.
    Anyway, with a proper consideration of 4-vectors we can make all the ideas more rigorous and there is no conflict in the units of measurement for the time component or spatial components of the 4-velocity.
    It is really only the formal 4-velocity of an object that must always have a magnitude of c and it's convenient that the 3 spatial components are a bit like the ordinary Newtonian 3-velocity of the object.

- - - - - - - -

Have you seen Penrose's description of two observers walking past each other?

    I'm not sure that I have, sorry.   Is there any online reference?
I can hazard a guess as to what it was about.

Best Wishes.

9

Physics, Astronomy & Cosmology / Re: Could the universe be smaller than the visible universe?

« on: 03/12/2024 01:06:13 »

Einstein's equations gave two solutions

A brief history of modern cosmology: Around 1915, Einstein produced a field equation describing the cosmos. The calculation generated an (unknown) constant of integration (as integration always does).
- Einstein's original paper omitted mention of this constant. It was mentioned in a later version.
- As usual in mathematics, you try to find some known condition that allows you to identify the value of this integration constant
- Einstein followed the cosmological assumption of his day that the universe was eternal and unchanging, and this "known condition" allowed him to define a value for this constant.
- Around 1925, Belgian priest Georges Lemaitre (perhaps with a Bible-inspired cosmology) saw in these equations the possibility of what we now call a "Big Bang"  creation of the universe. Same equation, different range of values for the cosmological constant, and different initial conditions.
- In 1929, astronomer Edwin Hubble saw that the universe was expanding. This confirmed Lemaitre's suggestion. At this point, the cosmological constant was assumed to be zero. Same equation, different value for the cosmological constant.
- In the 1970s, Vera Rubin saw that galaxies rotated in a strange way, and this led to the idea of Dark Matter. Same equation, same value for the cosmological constant, but introducing the concept that the mass of the universe is a combination of "normal" matter, and the dominant "Dark" matter.
- In the 1990s, the accelerating expansion of the universe was discovered, attributed to Dark Energy. Same equation, different value for the cosmological constant.

Einstein's field equation has proved remarkably resilient for over a century.
- New theoretical, computational and experimental techniques for investigating it have repeatedly confirmed it to an incredible accuracy
- With applications including black holes, GPS, gravitational waves, gravitational lensing and frame dragging
- Discoveries in this time have changed the interpretation of various parameters in the equation, but the equation itself has stood the test of time.
- Some very recent satellite measurements of the expansion of the universe have called into question just how constant this "cosmological constant" truly is. We will need more data to confirm if it has changed, and if so, in what manner
- An engineering "law": "All constants are variable" (under different conditions)

https://en.wikipedia.org/wiki/Einstein_field_equations#The_cosmological_constant

10

Just Chat! / Re: Theories to start a new world.

« on: 02/12/2024 22:58:48 »

Hi.

Religion is all about selling undisprovable hypotheses in order to control people's actions.

   No, that just sounds like human selfishness, corruption and some desire for power by a few people who have come to be in charge of the religion or else in charge of something else and just citing religion as supporting them.    Religion is about not wanting to be alone, left feeling pointless, worried about not existing any longer, seeking the answers to fundamental questions  etc. etc.   Things that you aren't going to make disappear just by not bringing any religion to the new world.
   c.f.   @paul cotter  's reply.
- - - - - - - - - -

I think you meant "non physics" science rather than "non physical" science.

    Physical sciences involve studying the inanimate stuff while Biological science is the study of the animate (living) stuff.   There's definitions on the web and it's reasonable to split science into these two broad categories.   I think I can say non-physical sciences and just hope people understood I meant Biological sciences rather than the study of nonsense with no physical basis.

- - - - - - - - -

It must be useful there and then

    Thanks for your time and response.   It's good and perfectly understandable.   It does have some comedy but is otherwise similar to the response first given by @paul cotter so probably won't get the best answer award.....  Which really doesn't matter anyway and would not change your life.

Best Wishes.

11

Just Chat! / Re: Should smartphones be banned from the dinner table?

« on: 02/12/2024 12:34:35 »

Further thought. I have attended a few committee dinners in pub restaurants. Time was that these were places for quiet conversation in an acoustically "soft" environment, separated from any live gigs in the "spit and sawdust" bar.

Nowadays the acoustic environment is  "hard" (no sticky carpets, big glass windows....) and filled throughout with umpteen decibels of piped noise, over which you have to shout to be heard by your nearest neighbor.

So it is quite likely that those under the age of 40 have never experienced conversation over a meal, and don't know how to behave at a family dinner.

12

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.

13

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

14

General Science / Re: Can an electron travel a bit in a copper wire for inertia?

« on: 26/11/2024 15:15:29 »

Save your typing fingers! "Free electricity" is not possible. The work done separating the ends of the wire will exceed any energy available to make electrons leave it.

The answer to a sustainable future for homo sapiens is to reduce our standard of living or reduce our population. The latter is obviously more desirable, saves a lot of effort, and costs nothing.

15

New Theories / Re: what is temperature?

« on: 25/11/2024 13:20:30 »

Hi.

    Thanks for your comments @alancalverd .    I think I can see what you're saying.
Although there isn't anything resembling an ensemble of particles inside your box, there is only one particle in the box, we can theoretically treat it as a confined ensemble of particles.    That theoretical ensemble of particles could have a temperature much as you described.
     
      I don't often sympathise with a lot of stuff that @hamdani yusuf  talks about.   However, temperature isn't the simple or completely objective thing that we may have thought it was after sutdying some school level science and there's not much wrong with discussing this in a science forum like this.   It can be fun to re-examine some of the stuff that you (we) thought we knew and understood.    All the words you may have heard at school like "we are only presenting some models and as you study more, you'll find that many of these models will be replaced with something else or possibly that the model is just wrong and fails to explain some things but there's no better model available at the moment" are actually true but the problem is that people do actually leave school and then there's no school reunion event to actually follow up with the discussion about this.   A forum like this one can usefully provide a place for such discussion.

      If you (we) end up teaching some young people then we'd better make sure we teach the syllabus but at least we can say those words in red   (.... we are only presenting some models..... ) with some genuine conviction.

      One of the things about "temperature" or "hotness" of an object that I don't think has been mentioned much so far is that it can depend on the place where the object is put.   I hope @hamdani yusuf  won't mind too much if I spend a moment discussing something about this here.

Let's start here:
        Temperature is a measure of a quality of a state of a material. The quality may be regarded as a more abstract entity than any particular temperature scale that measures it, and is called "hotness" by some writers.   The quality of hotness refers to the state of material only in a particular locality, and in general, apart from bodies held in a steady state of thermodynamic equilibrium, hotness varies from place to place....
     [Taken from Wikipedia under "Basic Theory" for temperature.   https://en.wikipedia.org/wiki/Temperature#Basic_theory  ]
     
What does it mean?    Well it could mean that some things, like a long rod, have a temperature of 100 deg C at one end and a temperature of 80 deg C at the other end -   temperature can be locally defined and vary from place to place.   However, that is almost certainly NOT what was meant.   They probably meant that even if the whole rod had a temperature of 100 deg C while it's measured in one place then if we pick the whole rod up and just put it in a different place, it's quality of hotness or temperature can change.

    An example:    The Zeeman effect describes how the energy levels occupied by electrons can split in the presecence of a magnetic field.
     We consider a theoretical object, a sink for all thermal energy, that we identify as being at 0 Kelvin (absolute zero).   If we put a test object into thermal contact with this sink then energy will flow from our test object to the sink   if and only if   the test object has a temperature above 0 kelvin.  So we have a way to know if our test object is at absolute zero.
    Now we have a test object that is a bit like a group I metal, with a single valence electron in its outer shell.  We'll have this test object in its lowest possible energy state.   In a place with no magnetic field, the electrons have no lower energy level they can fall to, we can make thermal contact with out idealised thermal sink and no energy will flow to that sink.   Our test object seems to have a temperature of 0 kelvin.
    If we move our test object to a region with a uniform but non-zero magnetic field, without deliberately adding or removing any energy to the test object, then the electrons wave functions become a superposition of the two energy levels available from the splitting by the Zeeman effect.   Alternatively, if you prefer to think of the electrons individually and more classically then you could say half of the electrons go into the lower energy level, half go into the higher energy level and overall the energy of the test object remains the same.    Either way you wish to consider it, there are some electrons capable of falling into a lower energy state.  So when we make thermal contact with the sink, some energy can flow into the sink and out of our test object.   It seems that the test object has a temperature above 0 kelvin now that it's in a place with a non-zero magnetic field.

   There's quite a few things about temperature that are strange and not as clear cut as we may have thought.   In General Relativity we don't often consider temperature as an important thing, it may not be fundamental or objective enough.   For example, the temperature of an ideal fluid doesn't appear in the stress-energy tensor but the pressure of that fluid does.   Similarly, cosmological "equations of state" relate energy density to pressure and don't involve temperature unlike the typical "equatons of state" that you may encounter in thermodynamics.   Pressure may be a bit more fundamental, objective, or useful as a property that an object can have rather than temperature.    I don't know.... it's all just a model but maybe a model where we recognise temperature as just an approximate and emergent property is a small step closer to the underlying nature of things.

    In that respect, I would differ from @hamdani yusuf 's  line of attack:   I'm not sure there is a lot of point trying to make a better or more precise definition for temperature.   It's just an approximation that is useful sometimes.

Best Wishes.

16

Physics, Astronomy & Cosmology / Re: What Causes This Optical Effect?

« on: 22/11/2024 12:44:58 »

Not disputing one word of what you have said but I fear you have got the "wrong end of the stick". The OP was talking about an illuminated room versus a dark exterior and your example was a detailed analysis of an illuminated room with daylight outside.

Mea culpa, but geometric optics is commutative!

17

Physics, Astronomy & Cosmology / Re: What Causes This Optical Effect?

« on: 22/11/2024 12:18:35 »

It's not about interior vs exterior, it's lighter side vs darker side.

When you look from the brightest lit side to the darker side, the light reflected off the window/net curtains/ half-silvered mirror is greater than the light transmitted through it from the darker side, so you only see the reflected light because your eye doesn't have sufficient dynamic range to see both.

Move to the darker side, and the light transmitted from the bright side is greater than the light reflected from the dark side, so you see through.

The way to see the "wrong" way through a "one way mirror" is to put your face right up against it, and shade around your eyes with your hands (the same way oscilloscope hoods work).

18

Just Chat! / Re: Where do I get my confidence to challenge established theories?

« on: 22/11/2024 10:19:05 »

High voltage, high current and high frequency (65000Hz) through the body of Dr Irwin Moon!!!

High current through the body? I think not. Skin effect is significant at 65 kHz and any current greater than 10 mA through the heart can be fatal.

19

New Theories / Re: what is temperature?

« on: 21/11/2024 11:06:40 »

ChatGPT's answer to my question

Why are you still asking ChatGPT and wasting bandwidth with it?

20

Physiology & Medicine / Re: What Are Chemical Burns?

« on: 19/11/2024 03:54:14 »

As mentioned earlier in the thread, spicy peppers are not actually corrosive, and won't actually cause true chemical burns.

The capsaicin interacts with receptors that typically sense heat and pain, and that interaction causes an artificial activation. If enough of the nerves in an area activate and send the pain/heat signals, the body will react as if it has been burned, so this is why chili peppers can trigger an inflammatory response (for example, if one handled extra hot peppers without gloves, the oils could trigger inflammation in the fingertips, bringing extra blood to the area, and causing swelling and redness).

However this is not actually a burn, not even a chemical one.

Chemical burns result when the body comes into contact with a substance and reacts with it. Common substances that cause chemical burns are strong acids or strong bases, which are able to react directly with the molecules that make up the flesh, and break them down into smaller molecules.

There are other substances that are not acids (strictly speaking, they aren't Br?nsted acids) but can react with water and/or biological tissues to produce acid. Examples of this would be things like allyl bromide (which slowly reacts to produce hydrobromic acid), or phosgene (which slowly reacts to produce hydrochloric acid).

Yet more substances can react with biological materials in a dazzling array of different types of damaging reactions. But across the board, they all end up causing chemical reactions that destroy the flesh. That is the simplest explanation.

There are also substances that release a huge amount of heat on contact with water (like dehydrated gypsum), which can give the appearance of producing chemical burns, but technically produce thermal burns by releasing significant amounts of heat on contact with flesh (which is wet, and releases more moisture as it is damaged).