41

Physics, Astronomy & Cosmology / Re: ELI5: Diffraction grating

« on: 28/11/2022 20:16:14 »

You could start here: https://en.wikipedia.org/wiki/Diffraction_grating

42

Physics, Astronomy & Cosmology / Re: Orbiting or descending into the black hole at the centre of the Milky Way?

« on: 27/11/2022 20:49:35 »

Mainly the MW is in orbit around itself.

And the mass of the Milky way is dominated by the (so far) invisible Dark Matter halo.

it looks like the stars are swirling down into the black hole

Out in the fringes (where we live), the stars are well-separated, most of the stars are in a fairly thin disk, have fairly circular orbits, and and have roughly the same angular velocity. So they won't interact very strongly with each other.

However, in the central bulge, stars are closely spaced, they have wildly different orbital planes, and the ones we can see near the central black hole have rather elliptical orbits, so the stars will transfer angular momentum between each other.

Some of these gravitational interactions will "cancel" angular momentum (if the stars have different orbital axes).
I expect that this will result in the central bulge flattening out over time - but the average distance from the central black hole will then be less than it is now. When stars are moving in a disk, they will have fairly stable orbits.

...that is, until the central black hole merges with another black hole; the incoming black hole will add angular momentum into the system on an entirely different axis, and once again send the stars off in all directions.
https://en.wikipedia.org/wiki/Sagittarius_A*_cluster

it looks like the stars are swirling down into the black hole

You inferred this from looking at a still image, and imagining the galaxy as a drain emptying in a whirlpool. This is not what "Whirlpool Galaxy" means.
https://www.nasa.gov/feature/goddard/2017/messier-51-the-whirlpool-galaxy

The Gaia space probe has been able to measure the velocity of stars in the Large Magellanic Cloud, and it is showing the stretching associated with being spaghettified by its close approach to the Milky Way. But the orbits are still roughly elliptical, rather than converging on the central black hole (if it has one...)
https://www.esa.int/ESA_Multimedia/Images/2018/04/Rotation_of_the_Large_Magellanic_Cloud#.Y4PLHulNzqU.link

43

Physics, Astronomy & Cosmology / Re: LHC costs, is it worth it?

« on: 19/11/2022 20:08:57 »

Is mathematics truly capable of explaining the laws of the Universe?

Newton's equation F=ma explains a lot about the universe, when combined with his equation about universal gravitation.

Are we capable of explaining everything? No. Much of the universe is outside our light cone, so we would have no way of verifying such a theory, let alone generating it.
- Are we capable of explaining the physics principles underlying everything we see? Maybe - we see with light (electromagnetic radiation), and physics has explored many interactions involving electromagnetic radiation
- Are we capable of explaining the physics principles underlying everything we feel? Definitely not yet! In our galactic orbit, the Sun feels the tug of Dark Matter, and we don't know what that is. The LHC has not yet turned up any likely particles as candidates.

44

Just Chat! / Re: Anyone here have any good penis jokes?

« on: 19/11/2022 19:59:03 »

This is not the place for them. We aim to keep the forum "family friendly", so children can safely come here for answers to scientific questions.

45

General Science / Re: Why is gold gold?

« on: 19/11/2022 19:55:47 »

The thing that flags on gold is the photo electric effect with it able to absorb blue end light

The photoelectric Work Function of Gold (5.1eV) is not that much different from Aluminium (4.08eV)
- But they are in the "wrong" order for this hypothesis - if gold absorbed blue light by the photoelectric effect, then Aluminium should do it even more strongly.
See: http://hyperphysics.phy-astr.gsu.edu/hbase/Tables/photoelec.html

For visible light, the range of photon energies is 1.63eV (red) to 3.26 eV (violet), which is less than the work function of gold or aluminium, so no electrons will be ejected. That is why the photoelectric effect is measured with UV light.
- Interestingly, Calcium, with a work function of 2.9 eV would see a photoelectric effect with visible light at the violet end of the spectrum
- But we usually observe Calcium in oil (no photoelectric effect) or air (coated with an oxide).
- Measurements of the photoelectric effect have to be conducted on bare metal, in a vacuum.

46

Physics, Astronomy & Cosmology / Re: LHC costs, is it worth it?

« on: 16/11/2022 20:33:14 »

smashing protons it can only go so far

CERN is investigating a successor to the LHC; one proposal would have a tunnel 100km in diameter, with the current LHC boosting the particles ready to inject into the new machine.
- They still haven't decided whether it will smash protons, or electrons & positrons, or... (and it isn't funded yet!)
- The new machine would also have new technology in the magnets, a spinoff from another expensive high-technology project, ITER (a nuclear fusion research reactor).
- At least ITER is easier to explain - if we can ever get fusion to work, here is a source of low-carbon base-load electricity!
https://en.wikipedia.org/wiki/Future_Circular_Collider

47

Physics, Astronomy & Cosmology / Re: Complex or real wave function?

« on: 15/11/2022 07:22:15 »

both (real & imaginary) components are important

As I understand it, the magnitude of a wave function indicates the probability of detecting the particle in a particular place.
- The magnitude includes both real and imaginary components

48

Physics, Astronomy & Cosmology / Re: LHC costs, is it worth it?

« on: 13/11/2022 07:14:06 »

The LHC cost about $US5Billion to build, and about $1Billion a year to run.
https://en.as.com/latest_news/how-much-money-did-cerns-large-hadron-collider-cost-to-build-and-who-paid-for-it-n/

The main member countries are Germany, the United Kingdom, Italy, France and Spain, with a combined population of 322 million people, or an operating cost of about $3 per person per year. Include contributions from USA, India, Russia, etc, and the operating cost is even lower.

With the large collider being built at CERN, the USA abandoned a project to build a competing device for a similar price. For big projects like this, a worldwide collaboration is a good idea.
https://en.wikipedia.org/wiki/Superconducting_Super_Collider

Scientific developments for the accelerator magnets and detectors of LHC has fed into better MRI machines and PET scanners. CERN researcher Tim Berners-Lee invented the World-Wide Web (which we use every day), and the CERN Grid Computer which stores and processes LHC results is the fore-runner of the internet's "Cloud" which we also use every day.

As always, how governments invest their money is a matter of hot political debate. But scientific and technological advances have changed our society radically in the past 50 years, and CERN/LHC has contributed some of that progress.
- The alternative to civilian R&D (like the LHC) is often military R&D, where the results are kept secret and don't benefit the public; the results of military R&D often go up in smoke, destroying social capital, rather than increasing it (as the war in Ukraine illustrates so graphically).

49

Physics, Astronomy & Cosmology / Re: Is there an experiment that shows the oscillation in the E field of light?

« on: 13/11/2022 06:53:22 »

If I ask the same questions in a different order, I get a different answer, which is a little disturbing to me

In my primitive understanding, passing light through a polarising filter is like a test or a measurement of the polarization.
- If a photon passes through the filter, it has "passed" the test, and you have measured its polarisation as being in-line with the filter.
- If you put another polarising filter at 90°, everything passing the first filter will fail the second filter.
- However, if you put a 45° filter in between two 90° polarising filters, you are conducting another test/measurement. The outcome of this measurement is that cos²(45°) = 50% cos(45°) = 71% of photons passed the second test, and 50% of that (ie one quarter) 71% of that (ie half) now get through the third filter (if they were perfect polarisers)

In a quantum world, taking a measurement changes the thing you are measuring. So it is no longer light polarised vertically, any photons passing the 45° filter are now polarised at 45°. And a fraction of these will pass the third filter.

Corrected, as advised below by Eternal Student...

50

Physics, Astronomy & Cosmology / Re: Is there an experiment that shows the oscillation in the E field of light?

« on: 12/11/2022 21:43:28 »

I understand that you can show polarisation of a microwave beam by building a wall with row of parallel wires.
- When the wall is oriented in one direction, it "short-circuits" the E-field and the microwaves are blocked
- Rotate the wall by 90°, and the microwaves get through, as the wires don't short-circuit the magnetic field.

A similar arrangement (on a smaller scale) is used to produce polarised lenses for visible light - there is a grid of long, parallel crystals in the lense.

51

Physics, Astronomy & Cosmology / Re: With unlimited budget, what would be your ideal space exploration project ?

« on: 11/11/2022 19:59:26 »

oxygen... I hear it's in short supply on mars

It's not so much a lack of oxygen...

It's more of a problem that what oxygen exists is bound up with pesky other elements like Carbon (CO₂), Silicon (Si_nO_2n) or Hydrogen (H₂O).
- Of these, water or water ice is the most valuable form of oxygen, as we need water for drinking, and Hydrogen makes a good rocket fuel.
- We have technologies that can split water into Oxygen & Hydrogen, given a suitable supply of electrical energy - and a source of ice...

52

Cells, Microbes & Viruses / Re: Flu crisis what crisis?

« on: 02/11/2022 08:25:57 »

Yes, antibodies do fade if they aren't regularly reactivated.

But there are suggestions that some people have retained an immune memory of similar influenza outbreaks from many years before, which is why children are often affected badly by influenza, and are major transmitters of influenza.
- This produces a "V" shaped age profile, affecting mostly children (never exposed) and old people (generally more frail)

Both Influenza virus and Coronavirus are RNA viruses, which means that they mutate quite rapidly
- They both have several animal reservoirs, which is an additional source of mutations.

At present, influenza is seasonal, peaking in winter months (apart from the past 2 years with masks).
- But COVID variants are still sufficiently transmissible that it doesn't need to wait for another winter season; we seem to be getting new waves about every 6 months

53

Chemistry / Re: Silicon based Life?

« on: 01/11/2022 09:20:32 »

Hydrogen....   That's no use on it's own

Since we are engaging in wild speculation (as science fiction authors have done for many decades)...

In its most general sense, the function of life is to redirect energy resources so as to produce a local decrease in entropy.
- A star (mostly Hydrogen, at least initially) has ample energy resources
- The flow of this energy can be redirected by magnetic fields (for example, magnetic fields throttle the flow of energy beneath a sunspot)
- So, hypothetically, you might have a form of life which is constructed from magnetic fields in the plasma of a star?

54

Physiology & Medicine / Re: Cat with electronic plug installed in forehead?

« on: 27/10/2022 21:50:50 »

Cats need your help!

Brain research requires accessing the brain.
- Doing early research on humans would be considered unethical until it has been proven to provide real benefits in animal trials.
- A lot of brain research was conducted on the nervous system of the worm C.Elegans; researchers have documented every neuron in its brain. ...it made scientific headlines a few years ago when some researchers discovered a new neuron that hadn't previously been documented!
- Most laboratory testing of mammalian brain function is done on rodents. Their brains are so complex that researchers struggle to understand it. Recently, optogenetics has been used, so there is an optical fiber connection to the brain, rather than an electrical plug

I do not see so much public support for the following campaigns:

C.Elegans need your help!

Rats need your help!

https://en.wikipedia.org/wiki/Caenorhabditis_elegans
https://en.wikipedia.org/wiki/Optogenetics

55

Physics, Astronomy & Cosmology / Re: Negative Space?

« on: 20/10/2022 21:41:59 »

If so could (negative space) be where anti matter is?

Antimatter definitely exists in our (+)3D space, as seen in some nuclear decays (which spit out a positron), and high energy particle accelerators like the LHC (which emit sprays of many kinds of antimatter). But this antimatter is short-lived and makes up a small amount of our universe.
- There is a long-standing mystery in physics about why our universe should be almost entirely made of matter, since virtually all nuclear reactions seem to produce equal amounts of matter and antimatter.
- Maybe you are asking "Could the bulk of the antimatter be in negative space"?
See: https://en.wikipedia.org/wiki/Baryon_asymmetry

Is a collision between particles that produces anti matter just a relapse effect across the "bridge"?

I don't think so.

The reasons is that there are some particles which are their own anti-particle, like the photon (and maybe the neutrino - but they interact so rarely that no-one can tell, see https://en.wikipedia.org/wiki/Majorana_fermion ).
- So if there is (+)3D universe where the normal matter lives, while antimatter lives in an imperceptible (-)3D universe, where do the particles live that are neither matter nor antimatter?
- We certainly perceive photons in our universe
- When an electron and positron collide, they emit a pair of gamma rays, both of which are visible in our universe
      - they don't disappear into a (±)0D universe
      - Because a photon can only propagate as an electromagnetic wave in a 3D space (and 4D spacetime)
      - One photon doesn't stay in our universe, and the other one disappears into a (-)3D universe

So I think there are some holes in the theory (maybe as big as the holes in your shower floor...).

opposite direction of a ... frequency

Neither frequency nor charge are vectors.

True, but there is a sense in which frequency can be negative, and that comes out of the Fourier transform of a signal.
If an electrical signal takes on real, measurable values, then its Fourier transform has (equal and opposite) frequency components.

But mostly we just regard them as a mathematical artifact and ignore them.

56

New Theories / Re: The Truth about Science

« on: 20/10/2022 09:41:34 »

The mystery is why there was a gap between the star being spaghettified (causing a bright blip), and then the production of a jet of material (causing another bright blip), with a gap of about 3 years.

One possible reason for the gap is that the star's interior has been swirling around in the black hole's accretion disk, slowly working its way to the inner disk, where it contributed to a brightening of the black holes' jet.

https://www.cfa.harvard.edu/news/weve-never-seen-anything-black-hole-spews-out-material-years-after-shredding-star

57

Technology / Re: What if to inject into gasoline or diesel 2CO + 3H2

« on: 18/10/2022 09:34:06 »

2CO + 3H2. Will the combustion be greater?

If you want the combustion to be greater, just use the H₂ in an internal combustion engine.
- Mix it with air, and you get quite good combustion.
- If you want more efficiency, feed it into a fuel cell, and drive an electric vehicle.

Some people call this the "Hydrogen Economy".
- But for vehicle applications, Hydrogen has a fairly low energy density - you need an enormous fuel tank in your car, truck or aeroplane!

58

Physics, Astronomy & Cosmology / Re: How do photons relay information across distances?

« on: 17/10/2022 22:23:52 »

how a photon relays information across various distances

To send information via photons (or any form of communication) requires:
- A sender
- A receiver
- A communications channel between them
- A common understanding between the sender and receiver of how to encode and decode the signals over the channel
- A common understanding between the sender and receiver of how to interpret the signals
- And because communication channels are not perfect, there is usually some mechanism to detect and correct lost or corrupted communications (eg "say that again?")

how a photon relays information across various distances

There are many ways to encode information on photons, and many things that you can do with it. The common methods we use with photons are:
- Writing
- Television & screens on computers and phones
- Mobile Phones, WiFi and radio
- Optical fibers
- In medical applications we use X-Rays, Gamma rays, infra red and radio waves, which are photons of different wavelengths, to communicate information about disease states outside of the body to a radiographer

The main advantages are that:
- It travels very quickly: 300,000km/second in a vacuum, pretty much the same speed in air, and around 200,000 km/second in water
- It travels very far in a vacuum (we can see the Sun, and distant stars), pretty far through air (on a clear day), and even penetrates a few hundred meters into the sea.
- It carries energy - almost all of our biosphere is powered by photons from the Sun.
- Plants use this energy to turn CO₂ into food (for themselves, and us)
- Many organisms are sensitive to light, because it helps synchronise their day/night circadian rhythm.

stop sign

Light from the Sun contains photons of many wavelengths (or frequencies, if you prefer).
- The white reflective pigment in the "STOP" letters reflects all these wavelengths
- The red pigment in the stop sign absorbs the green and blue wavelengths, reflecting the red wavelengths.
- Your eye focuses these wavelengths into a pattern onto the retina, where it is carried to your brain
- The translation of this pattern into the word "STOP" requires years of schooling.
- The translation of this word into you pressing the brake pedal in your car requires even more training

See: https://en.wikipedia.org/wiki/Communication_theory

59

Geology, Palaeontology & Archaeology / Re: How does fracking make sure no methane gas escapes?

« on: 17/10/2022 22:00:07 »

Some legislation attempts to ensure little methane escapes - but that is difficult as it is invisible, odorless and lighter than air.

You really need an infra-red camera to see leaks - like this video from a big methane leak from a storage facility in Aliso Canyon, California, back in 2015.

Methane heats the atmosphere more than carbon dioxide, but it is removed from the atmosphere quicker
- Overall, it is better to burn the methane (and do something useful with the energy) than release methane into the atmosphere
- Sabotaging undersea gas pipelines is not a way to do something useful with the methane...
https://blogs.edf.org/climate411/2008/02/26/ghg_lifetimes/

60

Technology / Re: Does wi-fi harm the environment?

« on: 17/10/2022 21:49:23 »

How bad is wi-fi to the environment?

Compared to what?

Rather than flying 1,000km (each way) to visit a customer in the next city, it is far better for the environment (and my time, and the cost to my employer and ultimately the public) for me to do a videoconference over WiFi.

Of course, only the first and last couple of meters of that videoconference are carried over WiFi.
-  I assume that you mean telecommunications in general
- The mobile phone in your pocket only uses WiFi while it is in the house. Once you get outside it switches to a cellular mobile network - similar technology, but on different frequencies (and financed differently).
- There is increasing interest in using satellites in Low Earth Orbit (LEO) to provide data and other communication services to people living in remote areas, plus planes and ships

In general, to send a signal farther, you need more power.
- Sending data 2 - 10 meters to a WiFi hotspot in your house uses very little energy
- Sending the same data 100-1000 meters to a cell tower takes more power
- Sending the same data 400km to an orbiting satellite takes even more power, and a much larger antenna at both ends
- That's why most data today is transmitted most of the way via optical fibers - the refractive index of the fiber redirects the laser beam into the core of the fiber, so that the signal is confined, and it travels farther with less loss and interference than wireless systems.
- Optical fibers are better for many purposes than wireless - except for the last couple of meters to where you are now. You don't want to be tethered to an optical fiber all day!

Electronics requires mining various minerals - but so does making a car or a home. The electronics in your pocket has advanced by a factor of a million in the past 40 years, and is far more environmentally friendly than the same functionality back then (as well as being thousands of times cheaper).

In contrast, cars and houses have improved their environmental credentials a bit - but at best by a factor of 2.

should we not be putting mobile phones in our pockets?

The signal levels put our by mobile phones are milliWatts for WiFi, and closer to a Watt for cellular mobile when you are far from the base station. Satellite communication takes even more.
- But all of this is negligible compared to the intense radiation from the Sun every time you walk outside.

Overall, I suggest that (where possible), rather than commuting an hour each way to work, you work from home (over WiFi), and at lunchtime you take your mobile phone with you, and go outside for a walk in the Sun - that is good for you and the environment.