1

Just Chat! / Re: Is there a universal moral standard?

« on: 07/10/2024 16:05:22 »

Has it violated the Geneva Convention?

Only to the same extent that the Allies did in WWII, and probably to a lesser extent.

Problem is that the Convention followed WWII when civilian casualties ran into the tens of millions (far  more than combatant casualties), so protection of noncombatants plays a significant part in the post-1949 rules of war.

The bleeding hearts now complain about civilian casualties where the enemy's armed forces are embedded in or under civilian establishments, which makes it impossible to project a just retaliation or to eliminate a threat from ground-based missiles without incurring significant noncombatant casualties.

The IDF attempts to minimise civilian casualties by issuing warnings of forthcoming actions but the destruction of infrastructure, and consequent depletion of civilian resources, remains inevitable.

The Convention necessarily acknowledges the right of States to self defence and hot pursuit of those that attack it. So on the basis that some modern warfare does not take place in trenches on open farmland, much of the Convention is irrelevant  and it behoves civilians not to give succour to those who wish harm to another State. 

Sensible response from an ex-CinC of the Lebanese armed forces on TV last week, suggesting that the official army should not interfere in an Israeli ground operation against Hezbollah. If only the general population of countries infected by such filth could see beyond religion and think about civilisation instead. 

2

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

« on: 02/10/2024 16:50:54 »

Oh dear, here we go, again. Word salad.

Indeed.  The prior posts have been removed for several reasons.

1) Nonsense in the main sections of the forum
2) Contained personal information
3) Had nothing to do with the topic title, hence is a hijack of a topic
4) Contained a bibliography which was nowhere referenced
5) Contained no content from any of said bibliography
6) Word salad as Paul points out
7) Duplicate posts

At least the first three of those violate forum rules.

3

Plant Sciences, Zoology & Evolution / Re: Could we eat wood?

« on: 02/10/2024 13:20:02 »

Wood has a nitrogen content of about 0.1% or less.
Proteins are about 14% nitrogen.
So wood is about 1% protein.
But, if the fungus "eats" the wood, oxidises the cellulose and lignin for energy and keeps hold of the nitrogen then it can accumulate enough nitrogen to make its proteins from.
And, in principle, we can eat that protein.
Mushrooms are about 3% protein.
That's not bad.
But by the simple expedient of feeding the mushrooms to pigs, we can get bacon (36% protein)
The question is how much effort is that compared to growing beans?
OK, in a nuclear winter, that's not easy.
But, if we still have a society, we can still burn oil, run the generators and run the grow lights.

We know how to do that so it might be the easy option.

How about taking teh wood, treating it with dilute acid, neutralising it with chalk and then fermenting it to alcohol and distilling that off.
The nitrogen is left behind.
Add slaked lime  and redistill it and you will get ammonia.
You can react that with acid and feed that "fixed nitrogen" to ruminants like cattle and sheep (which can probably digest sawdust- though I doubt they would be happy or healthy).
The best thing to do is not vote for people like Putin, or those who praise/ admire him.

It's all fun and games until the energy runs out. Everything else can be recycled.

4

Just Chat! / Re: Why do women have so many clothes?

« on: 28/09/2024 22:25:29 »

"Goeswiths".

The problem often starts from the bottom. One wet day, you discover that your strappy summer sandals really aren't suitable for standing in the rain, so you buy some cheerful red lace-ups. But you can't wear them with  a skirt and stockings so you buy some socks and a pair of jeans, but now you need a belt to hold up the jeans but that ensemble doesn't go with a cream handbag  so you buy a brown one for shopping and it looks ridiculous with a yellow cardigan so you need a blue sweater but that has a plunge neckline so you need a new bra and black is so nice but you can't possibly wear a sheer white blouse over it as you aren't a student any longer so a sensible red linen blouse sets off the sweater and as it's cold perhaps a chiffon scarf. All a bit dowdy now, so some big earrings to reflect the shoes but it's still raining so perhaps a leather jacket? Very biker-chic but you won't have time to change before going out to dinner so just add some heeled shoes so you can leave an impression on your friend's wooden floors, but they look ridiculous with socks and jeans so we need a skirt and tights. Keep the red blouse and ditch the blue sweater. Perfect, but not with a leather jacket, surely? So add a cream woollen coat. And a black handbag to match the shoes. And less flamboyant earrings.  Not sure about the scarf.......

And tomorrow is an office day. Grey suit, white blouse, no problem, but not with red shoes and a cream coat, surely?

Invited to a formal dinner with an erstwhile Boss, I watched her work through a dozen agonising permutations and then discovered that my dinner jacket had miraculously shrunk over the past several decades. Walked into the gents' outfitters and said "dinner jacket". Salesman looked at me and said "Rack on the right, try 46 regular. Blue or white shirt?"  Job done in 10 minutes, served as uniform in a dance band, will probably wear it in my coffin.

5

New Theories / Re: Gravity In Relative Motion - is there any solution?

« on: 28/09/2024 02:51:02 »

So does it mean that kinetic energy starts to be added to the inertial mass/energy of a body only when a certain velocity is reached?

No.  It would violate energy conservation if I did work on an object and no energy was transferred to it because it wasn't yet moving fast enough. This again is not unique to relativity theory.

If total relative velocity of our (me and the object in question) motion is equal to 0,99c - how can we know how our velocities are distributed in other frames?

The relative velocity addition formula can do the frame transforms for velocity.  Lorentz transforms are for coordinate transformations between frames.

Is there any difference between me incoming towards the object at 0,99c and object incoming towards me at 0,99c?

Yes.  The vector of one velocity is the opposite of the other.  Different objects are stationary in the two respective frames.

And what if in some other frame we (me and object) are incoming at each other with equal speed? Where the additional mass/energy will be added?

Each object contributes its own kinetic energy in that frame.

[/quote]And coming back to ISS and your answer - can you help me finding the fragment of text telling that relativistic mass becomes a 'thing' only at extremely high velocities and that it's effect is completely non existent below some specific velocity?[/quote]It doesn't have a minimum speed. It's a thing at any speed (even zero), but not very significant at low speeds where classical approximations are sufficient to express the KE of the object (E=mv?).

And if not that - should I understand that classical mechanics might lead to effects that are contradictory to effects of SR?

Classical mechanics is a good approximation at low speeds. Neither classical nor relativistic mechanics says that objects gain no kinetic energy until some minimum speed is reached.

So until some particular value adding velocity allows escaping gravity but then and then just like that - "Flop!" - and now adding velocity will start increasing gravitational pull?

Yet again, this is totally wrong. Stop asserting this.

Nope. [Einstein is] completely and utterly wrong about it. There's only 'as much' energy, that 'fits' into a given amount of mass (matter).

Only so much in stationary matter. There's no limit to KE, else again, energy conservation would be violated.

You simply can't get more energy from a given amount of matter than energy released due to annihilation - in which mass is literally turned into photons and stops existing as matter.

A fast moving small thing emits more energy (higher energy radiation) in such an annihilation. There's no limit to it. You seem to be in continuous denial of a simple theory, rather than taking the position of trying to learn about what you don't want to accept. You cannot falsify a theory that you refuse to attempt to understand.  I see little point in responding to somebody so closed to learning.

Your chosen quotes from wiki do not contradict this, except in their using the word mass to mean relativistic mass, which is an unconventional usage of the term.

6

New Theories / Re: Gravity In Relative Motion - is there any solution?

« on: 27/09/2024 23:38:45 »

I can defend relativty

1. there's a definitive & limited amount of energy in matter (according to Einstein it's unlimited) - equal to (half of) energy released to matter-antimatter annihilation.

Einstein is right. There is no limit to how much say kinetic energy one can give to a given object.  One can always apply a force on it to make it go faster, assuming one can find an energy source to do so.  So in the frame say some neutrino, the small bunny in my front yard perhaps has more energy than one stationary anti-bunny.

2. Body moving at 100% c

A 'body' has mass and cannot move at c, as Paul has pointed out. This is really basic stuff that shows you apparently know nothing about relativity theory.

gravitational attraction decreases gradually as source-object accelerates from 0 to 100%c

Gravitational attraction isn't a function of acceleration. Not one bit.

Because I really despise making theoretical calculations with real-life units like (kilo)grams, meters or seconds, I made myself a simplified system of units based on constant c (moving 1 space unit in 1 time unit).

They're called natural units, and in such a system, c=1 and can be treated as such in all equations.  But you assign c=10, which isn't a natural unit.

let me show you an example:
https://en.wikipedia.org/wiki/Mass_in_special_relativity#Relativistic_vs._rest_mass

Relativistic mass has been depricated since about 70 years ago.  By definition, mass is proper mass, and is frame invariant.  What varies from one frame to the next is momentum.  This is not a change in theory (The original SR paper did not treat mass as proper mass), but rather a standardization of convention.  Nevertheless, the idea of relativistic mass has an incredible presence on the internet, which is why chat bots use it so much.

Gravity is not a function of mass in relativity theory. It is a function of stress energy, which is frame invariant.

Basically according to Einstein there's no limit to the energy for any amount of mass (matter) - you can pack infinite amount of Giga-Joules into a single proton (or electron).

Or negative even. Potential energy is negative and there's no limit to the depth of a hole you can drop a proton into.

Well, sorry but in  my uneducated opinion, matter/antimatter annihilation turns WHOLE mass into energy and there's ALWAYS a finite & measurable amount of it released

Because you started with finite energy. Einstein doesn't say you can get more energy from a stationary thing. It has to be moving fast to have more energy than the stationary one.  If it's fast enough, you can do more work with it than the anti-matter thing, and it doesn't even have to disappear to do it.

and it's theoretically IMPOSSIBLE to get any more energy from matter.

So this assertion is clearly wrong.

Thing is, that for some reason physicists keep thinking that mass has a definitive amount energy at rest (inertial frame) but then you can 'pack it' with potential and kinetic energy to infinity.

If it has KE, it isn't at rest is it?  If it has PE, that is negative.  There's a limit to how close to zero PE can get, but it isn't really defined where zero is. I.E. there's not a place you can be that is free from gravitational potential.

Let's take a theoretical comet/asteroid entering edge of Earth's atmosphere at a relatively small (flat) angle - question: Will making the asteroid/comet faster increase or decrease the chance of it hitting Earth?

Bunch of problems with the pic:  The comet cannot be a comet since it is moving too slow. It is clearly in eccentric orbit about Earth, while comets orbit the sun and move much faster relative to Earth when in its proximity.
The tail of the comet points the wrong way. It should extend to the right, not down where you drew it. A comet tail is not a wake, despite all the popular images depicting it that way.

That aside, if the comet takes the same initial trajectory but is moving only a tad faster, it will have less time to accelerate to the right as you depict. It will miss. This is basic Newtonian mechanics and all of this has squat to do with relativity theory.

In Einstein's model increasing speed = increasing energy = increasing mass what should lead to stronger gravitational attraction

This is completely wrong. Relativity theory says no such thing. Mass is not a function of speed. Gravity is not a function of mass, at least not directly.
Please do not say what Einstein's model predicts if you don't know how (and when) to apply the model. It is a straw man fallacy.

My model predicts something directly opposite - the faster the comet moves, the less it is attracted to Earth

This is also wrong. Yes, it will miss, but because of what Newton says, not because the attraction is less.

What Einstein's model is suggesting is that the faster the interplanetary bearing ball will be moving in relation to Earth (stripped out of the atmosphere), the stronger it will be attracted to the surface - and that a slower cosmic bearing ball has bigger chance of escaping Earth gravity.

Totally wrong. Relativity theory says no such thing.

Ok, here's question to those willing to stand in defense of Einstein's model - let's have 2 bodies of equal mass accelerated simultaneously at the same rate to relativistic velocities - so that both are moving at the same speed next to each other (appear stationary to each other)

Gravity isn't a function of acceleration.  So you're saying that you still have two objects that remain relatively stationary.  Gravity between them (in their own frame) will be unaffected per the first postulate of SR.

- will the increased velocity of those objects (observed in some other frame) have any effect on gravitational interactions between those accelerated bodies or they won't observe any difference?

In a frame in which the two objects are moving fast, the two objects will accelerate towards each other more slowly.  Less acceleration, not more like you describe.  It will take more time for them to collide than they would in a frame where their mutual center of mass was stationary.  In a frame where they're moving at 0.866c, they'll take twice as long to collide with each other.

I'm pretty sure (like 85-90%) that not even the most loyal supporters of Einstein's model  can tell with >50% certainty what the model actually predicts - and if some actually can make such prediction, it will most likely go against predictions of some other Einstein supporters...

The validity of a model has nothing to do with a vote of support. Plenty of people support relativity without understanding it. Some support alternative theories, and a small fraction of those understand both Einstein's theory and their own choice.  Supports relativity does not imply that one can make correct predictions.

As for myself - I literally have no idea what Einstein's Relativity tells us about such/similar scenario

You're sure making an awful lot of incorrect assertions about it for somebody who admits a lack of understanding.

So ok, one more 'scenario' - what would happen with ISS if SuperMan or some other OmniMan would simply stop it's motion around Earth?

Hope they take their time about it.  The ISS is delicate and does not take kindly to large forces being applied to a small area.  Irrelevant, I know.  We assume it is sturdy for this exercise.  We assume Superman can exert reactionless force, but only because it doesn't change the answer.

Let's say it would stop moving right above my house and then would be left 'hanging there' not moving in relation to surface (at least horizontally) - what would happen then with it?

Nothing to do with Einstein.  It would fall somewhat to the east of your house after around 5 minutes.  East is due to Coriolis force.
If the object has sufficient altitude, it won't hit Earth at all. If it has even more altitude, it won't even lose altitude, which is how geosync satellites manage to stay put despite not moving in relation to surface.

Now, in this case I can at least try figuring out what Einstein's model predict in similar situation..I'd say that according to Einstein, ISS would simply keep 'hovering' there endlessly or maybe even it would slowly 'drift away' from Earth.

Seriously, you thing Einstein would suggest that??  This is pretty hard evidence of crackpottery.

Why I'd say so? Well, since it stopped moving in relation to Earth's surface, it's energy decreased and so did the gravitational pull towards Earth - that's how I'd see Einstein's model..

A stopped thing still has mass, which is non-zero energy. Surely you don't think otherwise. OK, it seems you do...
If you want us to take your posts seriously, take seriously the thing with which you disagree.

What my model predicts however, is that I'd have at best 10 minutes to move most important stuff from my house before couple hundreds (thousands?) tons of 'space junk' would turn it into a landing pod (although 'falling pod' seems to fit better) - it would simply start falling down from it's orbit like 2 seconds after it's motion would stop...

1) half that time  2) it will miss  3) it starts falling right away (just as it is doing now), not after 2 seconds.


I cannot quote the copilot answer since it isn't text, but almost everything in it is completely wrong, and is a fine example of why it is terrible to ask any chatbot questions on theories about which it has no actual understanding.

7

Technology / Re: Nuclear generation produces green energy?

« on: 27/09/2024 16:36:57 »

To collect it as carbonate would involve huge quantities of a basic substance

..... such as calcium oxide, made by heating calcium carbonate  to drive off the carbon dioxide.....or sodium hydroxide, made by electrolysis, using electricity made by, er, burning carbon......

Green plants are the only sensible sinks for CO2, which they turn into food and building materials.

8

Question of the Week / Re: QotW - 24.10.04 - Do snails get dizzy?

« on: 27/09/2024 12:56:21 »

do snails get dizzy?'

No. Getting dizzy is a byproduct of a vestibular system, a feature of vertebrates.  This system detects angular acceleration, and it is the detection of the angular acceleration of the cessation of spinning that makes one dizzy.

Snails instead have statocysts which detect linear acceleration, which gives them a sense of orientation, but not of spinning.  A snail in a car wheel would feel heavy linear acceleration, but essentially constant orientation (radially outward).

9

Physiology & Medicine / Re: Is There Any Safe Amount Of Smoking?

« on: 19/09/2024 23:40:06 »

Is There Any Safe Amount Of Smoking?
No. (Unless you are already on your death-bed).
In principle a single molecule of some carcinogen like benz alpha pyrene can create a change in  a DNA strand which leads to a mutation which causes cancer and kills you.

But the odds on that are pretty thin.

It's also reasonable to say that, if you are already 100 years old when you take up smoking, you won't live long enough for it to give you cancer.

So it's a statistical thing. The slightest exposure is an increased risk- but it's not a big risk.

Have a look at this

https://en.wikipedia.org/wiki/Micromort

10

Physics, Astronomy & Cosmology / Re: What would a Venusian webcam be made out of?

« on: 12/09/2024 12:55:50 »

No argument on pcb or pbb. Not all of these are equally bad, the determinant is whether there is an ortho halogen which prevents the biphenyl from being flat(can't remember if the flat or skewed version is the dangerous one). Unfortunately most of these were mixes of isomers so no way of there being a safe pcb(pbb). I came across a lot of these in old capacitors and transformers. 

The ones with an ortho halogen are non planar and thus unable to intercalate into DNA so they are less toxic. (But not "non toxic")
The word "intercalate" was used for such behaviour because, prior to being adopted by toxicologists, it didn't get out much. It was used for "putting February the 29th into the calendar". I think geologists might also use it.

11

New Theories / Re: what is temperature?

« on: 11/09/2024 18:43:01 »

Try

https://electronics.howstuffworks.com/led.htm

12

New Theories / Re: Can one switch magnetic flux with a ferromagnetic material?

« on: 11/09/2024 11:33:43 »

Just for the record, the impossibility of breaking the conservation of energy is one of the few laws of nature that's not just experimentally true; it was mathematically proven about a hundred years ago, by Emmy Noether (who should be more famous).
https://en.wikipedia.org/wiki/Noether%27s_theorem

So, in order to convince me of any "free energy" machine, you need to start by showing why the maths there is wrong.

13

New Theories / Re: Is Amino Acid a misnomer

« on: 11/09/2024 10:35:47 »

Here is a discussion I had with the Copilot AI regarding how "Amino Acid " is a misnomer. What do you think?

https://1drv.ms/w/s!AkkAzGDByUeBqJ8emzWrUNUoPOpQNA?e=HN2Kk2

I think you should stop wasting copilot's time with nonsense.
It has important things to do like helping students cheat on their homework and drawing bad pictures.

I also think you should learn some science.
Try the Khan academy.

14

New Theories / Re: what is temperature?

« on: 09/09/2024 11:34:13 »

They show that the concept of temperature is not as well defined as some of us might have thought.

That's a bit like saying that, because you can't divide by zero, we don't understand division.
We can't say what the temperature of a non thermal system is.
That doesn't mean we don't understand temperature.
It means that we understand that there are things to which it does not apply.

We can't tell you the thermodynamic temperature of the inside of a fluorescent light bulb when it's running.
We can't tell you the temperature of love or Thursday either.
That's not because we don't understand temperature.
It's because we understand it well enough to realise when it does not apply.

15

New Theories / Re: Could quantum mechanics be wrong?

« on: 08/09/2024 02:49:37 »

Hi.

Can quantum mechanics explain the generation, propagation, and reception of radio waves?

Short Answer:
   Probably not in an easy way for human beings to understand. 
   It probably is possible to use QM and apply a suitable interpretation of probabilities or the frequency of detection of photons to re-create the usual gross-scale classical radio wave propagation results - but this would be complicated.
   At the fundamental level, in most QM models there aren't any "radio waves".   So the problem starts with the way the question was phrased.

Medium detail / further discussion:
     The name "radio wave" that you are using in the question describes a phenomena that we (human beings) have come to ascribe some meaning to.   This thing,  "a radio wave", is an essentially classical physical phenomena.
    We imagine a radio wave as a ...  (you know) .....  spread out and continuous wave thing.  We expect to be able to measure an Electric and a Magnetic field and a radio wave will be a suitable oscillation in these fields.  There are many versions of Quantum Mechanics but most of them don't have that sort of thing as their subjects or objects of interest.   The simplest QM models consider all objects as if they are particles.   For example, we might consider a particle of light, a photon, as a suitable QM object but we do not consider an e-m wave as a suitable QM object.    QM objects just happen to have a wave function associated to them BUT they are essentially discrete particles and would always be detected as a discrete particle.
      More advanced QM theories, such as the mainstream versions of QFT, will consider the most fundamental objects to be fields.  For example, there will be a photon field that exists everywhere in space.   The thing we call a photon would not be treated as a fundamental QM object, it is just how we may interpret a certain oscillation in that underlying photon field at some place.    So, in QFT, there is a photon field but there is NOT any fundamental Electric field or Magnetic field.   These things, the electric and magnetic fields are just gross-scale fields that can emerge from the more fundamental fields of the particles in the standard model of particle physics.   QFT doesn't aim to deal with oscillations in the Electric and Magnetic fields, it only deals with the fundamental particle fields.   You need to add a layer of interpretation on to the top to translate what happens in these fundamental particle fields into something that can be observed in the gross-scale Electric and Magnetic fields.   That can be done in many versions of QFT but is rarely simple.
    When you are asking about "a radio wave", you have moved attention to something in terms of the ordinary (or gross-scale) Electric and Magnetic fields and not on any fundamental object (a photon in simple QM, or the photon field in QFT).   So the question cannot be answered without translating the results of QM back into something classical involving the Electric and Magnetic fields.   One of the simplest or most naive ways of making this translation is to just analyse the probablities or frequencies with which a QM object would be found at some place and time.   So, we might imagine that an e-m wave is a collection of many photons or that an experiment involving one photon has been done many times and the e-m wave we observe is the combined average of all of these.

Example:    If you could fire just one photon through the usual double-slit experiment apparatus,   then you probably won't get an interference pattern on the screen at the end.   Instead we think you'll get just one spot to glow on the screen.   However, if we repeat the experiment many, many times then we expect to see that the places where the screen glows and how often that bit of the screen glows will correspond to the usual interference pattern for a classical wave being put through that apparatus.    So, one individual photon does NOT behave like an e-m wave - but a thousand or a million of them would seem to reproduce classical radio wave-like patterns and behaviour.

NOTE:   I'm really not convinced anyone has actually done a genuine version of Young's double slit experiment where only a single photon is fired with a clear interval of time before the next is fired.   However, this demonstration gets close and claims to be using such a thin and dim stream of light that only "a few" photons per second will be produced.
https://sciencedemonstrations.fas.harvard.edu/presentations/single-photon-interference


   So, the important point is simply that "a radio wave" isn't the normal subject for any QM model.  It demands some form of interpretation to put the results predicted by any QM model back into terms which would make sense when you consider "a radio wave".   
   If we wished to be controversial we would say "there are NO radio waves... just QM objects that get detected at certain times and places.  On a gross scale, that looks like a radio wave is there".    ... However... I'm not that controversial or convinced that a simple QM model is some ultimate truth....  there are many versions of QM, all have some use and classical e-m theory is also extremely useful.   

Another minor note:    Your (Hamdani) extracts produced by Gemini seem to be blending many different versions of Quantum Mechanics.    For example,  QFT is a specialised theory and there are still about 3 versions or flavours of QFT that are in current use.   I don't think Geminii is reliably identifying where things can and cannot be combined.   For example, the simplest QM models are not like QFT.   They will involve the original Schrodinger equation, which is shown here:



That has a mass term, m, in the Hamiltonian for the QM object under consideration    (it's in the square bracket, h squared over 2 m).   This means it's actually useless for photons which should have 0 rest mass.   None the less, we (physicists) do generalise a lot of results from such a QM theory for massive particles to massless particles like photons.  For example, the Youngs double slit experiment can be modelled for electrons or even bigger particles like carbon bucky-balls.  We can (and have) then done experiments with these things and obtained a good match with the predictions from the simple QM model.   It is natural to assume a similar thing for photons, even though the zero mass term would technically make the simple QM model invalid.   If you read what I've said (above) about firing single photons then you'll hopefully notice that I've got phrases like "we think".   
     I believe that how you reconcile a classical radio wave with a suitable QM object ("a photon") is subject to a lot of interpretation. 

[Disclaimer:     I'M NOT AN EXPERT.  ]

Best Wishes.

16

Physiology & Medicine / Re: What liquid solution is best for a portable commode?

« on: 07/09/2024 20:16:13 »

Splash.
You should use water.

17

Question of the Week / Re: QotW - 24.09.06 - What is the shutter speed of the eye?

« on: 02/09/2024 10:25:19 »

Focal Length
The human eye has a fixed focal length of around 22mm, which gives a similar field of view to a traditional film camera with a 50mm focal length.

But camera lenses come in a wide variety of focal lengths - and a camera with a zoom lens might have a range of 60:1 in focal length (and corresponding wide range in field of view). 

Saccades
The human eye does not focus on just one image, but darts around parts of the image, allowing the high-resolution macula to dwell on different parts of the image for short periods of time. Saccades are the quick movements from one part of the image to another, occurring around 3-5 times per second, and lasting about 50ms each time. The brain suppresses the blurry image during the saccades, making them effectively unconscious and invisible to the viewer.
- The image collection time on one part of the retina is limited to 200-300ms, which could be considered the maximum "exposure time"
- But the brain is able to build up a detailed image across a number of saccades, forming a composite image like the popular "panorama" photo, or "stacking" in astrophotography.

An interesting comparison here... They suggest that the human eye can't see any more detail after looking at a scene for more than 10 to 15 seconds:
https://www.cambridgeincolour.com/tutorials/cameras-vs-human-eye.htm

18

Question of the Week / Re: QotW - 24.09.06 - What is the shutter speed of the eye?

« on: 01/09/2024 22:57:24 »

This means they can collect a lot more photons, under the same conditions.

Er, sort of. What matters is the brightness of the image, and for a given object this is principally determined by the ratio of aperture to focal length of the lens. This is conventionally specified as an inverse ratio f/n and for most cameras the largest aperture is around f/2, fairly close to the fully dilated human eye at f/3. Telephoto lenses bigger than f/4 are a bit unwieldy.

I heard that the human eye requires two photons to strike the same cone cell within a short period to register a flash of light.

Interesting. The same applies to photographic film. You need two visible photons to strike a single grain in a short time for a latent image to form. Under very low intensities, this causes "reciprocity failure" where the apparent sensitivity of the emulsion decreases with decreasing image brightness.  Astronomers used to "pre-fog" their plates to increase sensitivity - something of a black art probably lost nowadays thanks to  CCD imagers.  It also explains why fine grain photographic emulsions are less sensitive (typically ASA 50 - 64) than coarse-grain (ASA 1000) materials.

19

New Theories / Re: what is temperature?

« on: 01/09/2024 15:29:24 »

Hi BC, I have repeatedly told him to forget these bots and pop-sci videos and obtain some good textbooks. Alas, this has been in vain and I predict confusion ad infinitum.

Bots are cheap, easy and "convincing".
The fact that they don't believe there are three Rs in strawberry is, apparently, less important.

https://www.inc.com/kit-eaton/how-many-rs-in-strawberry-this-ai-cant-tell-you.html

That's not a problem because anyone can just count them and laugh at the stupid bot.
But it's a massive problem if you are trying to find the answer to something where you don't already know.
It's not really a new problem. Google, Lycos, AskJeves etc all screwed up royally in their early days. They got better but they are still not perfect.

20

Question of the Week / Re: QotW - 24.09.06 - What is the shutter speed of the eye?

« on: 01/09/2024 11:42:03 »

Some thoughts...

Aperture
The human pupil size varies from 2 mm diameter in bright light to 8 mm under dark conditions. Smartphone camera lenses are in a similar range.
However, consumer hand-held cameras have a light-collecting diameter of around 20mm, and perhaps 100mm with professional telephoto lenses. This means they can collect a lot more photons, under the same conditions.

Fastest Detectable Event
For both cameras and the human eye, extremely short events can be detected if they generate enough photons during the period when the camera aperture (or eyelid) is open. So this is not a characteristic of a camera or the eye.

Minimum Exposure Time
As Alan mentioned, the flicker fusion frequency of the human eye is around 20 frames per second for most people, so you could say that the minimum exposure time for the human eye is around 50ms.
- Some consumer cameras have a minimum exposure time of 1/1000 second, and are able to freeze very fast events which are a blur to the human eye.

Maximum Exposure Time
When making star trails, or using a tracking mount, astrophotography can use exposure times of hours.

The flicker fusion frequency suggests that the maximum exposure time of the human eye is somewhere around 5-10ms in bright conditions.
- Under low-light conditions, the human eye is able to integrate light over a longer period - but I suspect not more than a second. So you could call this the maximum exposure time.

Photon Sensitivity
In modern astronomical CCDs, about 80% of incoming photons striking the sensor will generate a detectable charge in a pixel (the rest are reflected, or strike wiring, etc).

I heard that the human eye requires two photons to strike the same cone cell within a short period to register a flash of light. This will reduce thermal noise, but also reduces sensitivity compared to a CCD camera.

Thermal Noise
Thermal noise generates lots of charges all the time in a CCD camera, so to improve the signal-to-noise ratio, visible-light astronomical telescopes are cooled to liquid nitrogen temperatures.
- Infra-red telescopes like James Webb must be cooled to <7K.
- With a non-cooled sensor, consumer-grade cameras need to collect a lot of photons to ensure that the image stands out above the thermal noise.
- To reduce thermal noise, consumer cameras typically use tricks like taking a reference exposure with the shutter closed, to measure the average thermal noise, and subtract that from the image with the shutter open. This works better with relatively bright objects which generate more than half of the charge of the thermal noise.

Colour Sensitivity
Consumer cameras are able to take colour photos under very low-light conditions, if the exposure time is long enough.

However, the human cone cells which detect colour are only effective under brightly lit conditions; in the dark, human eyesight falls back to the black-and white rod cells, with lower resolution than the cone cells of the central vision.