101

That CAN'T be true! / Re: New model of the Universe.

« on: 04/01/2021 08:14:10 »

How could MRO have lost 11.2-2.9 = 8.3 km/s of velocity during flight through space with zero resistance?

Mars is farther from the Sun than the Earth.
- So a rocket launched from Earth will lose speed as it climbs out of Earth's gravitational field
- It will lose more speed as it climbs out of the Sun's gravitational field.
- It will gain a bit of speed as it falls into the gravitational field of Mars - but not as much as it lost climbing out of Earth's gravitational field (since Earth is much more massive than Mars).

In a classic Hohmann Transfer maneuver, a rocket will start from an inner circular orbit (say, at the radius of Earth's orbit), and accelerate to become an elliptical orbit
- This elliptical orbit will have a perihelion at the radius of Earth's orbit, and an aphelion at the radius of Mars's orbit.
- If the rocket did nothing when it reached the radius of Mars, it would fall back towards the Sun, as it's radial velocity away from the Sun has reached zero, and it's angular velocity around the sun is too slow to maintain a circular orbit.
- So when you reach the target orbit, you need to fire the rocket to increase the rocket's speed to keep it in a circular orbit at the radius of Mars's orbit.

This simple Hohmann transfer assumes no mass at the destination.
- In fact, the gravitational attraction of Mars means that the rocket gains some velocity as it approaches Mars.
- By positioning the satellite's arrival relative to the position of Mars, you can cause the satellite to get a gravitational assist, either to increase or to reduce its velocity. This slightly reduces the amount of rocket fuel you need to carry.
- However, if you want the satellite to be an a low orbit around Mars for ground observation, you need to reduce the relative velocity to Mars by a considerable amount, or it will go shooting past (a flyby), or end up in a high orbit.
- So MRO needs to increase it's radial velocity around the Sun to stay in orbit near Mars, and shed most of the velocity built up as it approached Mars, for a Mars Reconnaissance mission.

See: https://en.wikipedia.org/wiki/Hohmann_transfer_orbit
https://en.wikipedia.org/wiki/Gravity_assist

102

That CAN'T be true! / Re: New model of the Universe.

« on: 04/01/2021 07:46:38 »

how big should a comet be to provoke a huge explosion on the far side of the Sun?

It can be 0 m in diameter.

The Sun has a lot of pent-up energy in its magnetic fields. These can reconnect at any time, causing a huge explosion, with no comets involved at all.
- Reconnection tends to happen more frequently when there are multiple sunspots on the surface of the Sun
- Which tends to be more common at a solar maximum

The above images are timestamped 1st October 2011
- And in fact the sun was very active in late 2011
- This suggests that the comet was a coincidence, rather than a cause
See: https://en.wikipedia.org/wiki/File:Solar_cycle_24_sunspot_number_progression_and_prediction.gif

103

Plant Sciences, Zoology & Evolution / Re: Why is compost black?

« on: 04/01/2021 07:38:41 »

Is there a relationship between humus and humins?

104

Physiology & Medicine / Re: Even though it's not licenced for under 18, should they get corona virus vaccine

« on: 03/01/2021 23:35:34 »

If we could send people to educational centres to teach them to control their immune system we could defeat Cancer

By "educational centres":
- An intellectual understanding of cancer won't help you defeat cancer (although an intellectual understanding of the dangers of smoking or sunburn might help you avoid cancer in the first place).
- However, if we could educate the immune system to recognize a cancer that you have, that may be effective in killing that cancer.

Monoclonal Antibodies are very targeted, and probably won't work on another cancer type in another person (or even all cells in a particular cancer in 1 person).
      - Because cancer cell genetics differ radically from each other, even in the same cancer mass
      - High development cost/small number of eligible patients = ridiculously high prices (eg $100,000.00 for 3 months of treatment).
      - Your body eliminates antibodies, with about half disappearing every 2 weeks.
      - These therapies indeed mean that your body does not develop it's own immunity to the cancer, so the treatment must continue as long as you live (or as long as the cancer lives, which is usually the same thing)

In contrast, with a Vaccine for a pathogen like SARS-COV2, one vaccine can work in almost anyone.
      - Because all viruses are clones of each other with the same genes (and some copying errors).
      - High development cost/large number of eligible patients = much more reasonable prices (eg $3-$60 for >6 months of protection).
      - A vaccine means that your body does develop it's own immunity to the pathogen which continues beyond the actual treatment itself, so it exercises your immune system more than a Monoclonal Antibody
 See: https://en.wikipedia.org/wiki/Monoclonal_antibody_therapy#Cancer

Rather than targeting the cancer itself (which has almost unlimited variability), Checkpoint Inhibitors target the mechanisms by which cancers evade the immune system (of which there are several fairly common ones which occur in many types of cancer)
- Many pathogens also use tricks to evade the immune system once they have established an infection; you could target these, but it's better to attack the virus before it causes an infection (with a vaccine).
See: https://en.wikipedia.org/wiki/Checkpoint_inhibitor

Conclusion: Effectively, a vaccine is an "educational centre" for the immune system - and a lot more effective than our attempts at producing "educational centres" for cancers.

105

Physics, Astronomy & Cosmology / Re: Why do Microwave Oven Plates Spin ?.

« on: 03/01/2021 22:45:59 »

I've not tried it myself, but I understand that you can demostrate this experimentally:
- Remove the foil wrapping from a large chocolate block
-  place the chocolate block in the microwave, supported so it doesn't rotate.
- Give it a burst of (say) 40 seconds on full power
- you will find some parts of the chocolate block melt, while other parts remain quite solid

As a bonus, you can also measure the speed of light!
See: https://www.thenakedscientists.com/forum/index.php?topic=11200.0

Hot and cold spots is not a good arrangement if you are trying to kill all the bacteria in a chicken!
- The rotating plate makes the heating more uniform

106

Geology, Palaeontology & Archaeology / Re: Could the rings of Saturn be a good place to find fossils?

« on: 03/01/2021 22:36:28 »

Wouldn't this extreme multiplicity of possible targets, make it very difficult to get a probe to zero-in on any one of them?

If you place an orbiter at the right radius and speed, it will be stationary relative to the ice blocks.
- It can then duck in and collect a sample of ice from the nearest block for imaging and chemical analysis
- and a larger ice sample to be dissociated and stored as fuel to move it on to the next block to be sampled

Sampling a variety of the rings would be a good idea, as well as imaging some of the "shepherd moons".

107

Technology / Re: The most advanced space technology you ever heard about

« on: 03/01/2021 22:29:12 »

Except if fluorine was used, but that element is so reactive it eats away its own metal fuel-pipes -unless the pipes were made of fluorite

You can also make them out of Nickel. Fluorine reacts with Nickel to produce a protective layer.
For the pipes, start at 4:30.
Watch the lot for video of Fluorine reacting with various chemicals...

108

General Science / Re: The journey to the red planet: does humanity need Mars colonisation?

« on: 03/01/2021 22:14:54 »

We could fight our wars on Mars.

I would prefer it to be treated more like Antarctica - each country develops their own base, and they are willing to help each other out if they get into trouble.
- The whole thing is done in the context of a treaty which bans military activity, specifically including nuclear weapons
- And an associated treaty protecting Fauna & Flora

The hardest part may be the ban on disposing of nuclear waste.
- In the case of Antarctica, it is possible to keep supplying diesel fuel. Not possible for Mars (plus there is no natural oxygen to burn it).
- In the case of Antarctica, it was possible to remove the US nuclear reactor, and clean up the mess it made. Not possible for Mars.
- So the whole settlement will probably need to run on solar power (wind power being very diffuse there)

See: https://en.wikipedia.org/wiki/Antarctic_Treaty_System
https://en.wikipedia.org/wiki/Agreed_Measures_for_the_Conservation_of_Antarctic_Fauna_and_Flora

109

COVID-19 / Re: Another conspiracy theory? Flu Vaccine raises Risk of COVID death

« on: 03/01/2021 08:28:39 »

his claim that the Flu vaccine raises the risk of COVID death

When it looked like COVID-19 was going to be a Big Thing this year, the Australian government started a big advertising campaign to get people to take up the seasonal flu vaccine (which is free for over-65s, people with chronic conditions, and subsidized for everyone else).
- Since they were starting a campaign of free COVID testing, they didn't want flu patients swamping the COVID testing,
- And they didn't want (preventable) flu cases from clogging ICU beds that could be used for (non-preventable) COVID cases.
- They didn't want COVID patients catching flu in hospital (and vice-versa), which would have made the outcome worse for both groups!
- Through the winter months, it was also mandatory to show evidence of flu vaccination before visiting aged care homes (this requirement has been relaxed during the summer months - I was able to visit my mother-in-law last week without showing my flu certificate)
- Flu vaccination, in conjunction with social distancing has really reduced flu rates this year. See Figure 1, in the following link:
https://www1.health.gov.au/internet/main/publishing.nsf/Content/cda-surveil-ozflu-flucurr.htm/$File/National-Influenza-Season-Summary2020.pdf

As statistics show, Australia has a pretty low rate of COVID infection & death
- So I would argue that the seasonal flu vaccine reduces COVID deaths - at least in the sense that it allows better detection and control of COVID cases.

110

COVID-19 / Re: When will we be able to stop wearing face coverings and stop social distancing?

« on: 03/01/2021 08:08:18 »

...why the virus... becomes virulent after 10 pm.

It's because as the evening goes on, the voices become louder, and any social distancing evaporates...

Even discounting this effect:
- If people stay for 6 hours instead of 1 hour, their exposure is 6 times higher (assuming the number of people is capped)
- If people stay for 6 hours instead of 1 hour, their exposure is 36 times higher (assuming the number of people is not capped)

I visited an art gallery today. After signing in, a sign at the door read "Please limit your visit to 30 minutes"  - admittedly, it was a pretty small art gallery, and numbers were capped, according to another sign at the door...

111

Just Chat! / Re: what do academics do after leaving academia?

« on: 03/01/2021 07:56:08 »

Old academics never die - they just lose all their faculties...

112

That CAN'T be true! / Re: New model of the Universe.

« on: 02/01/2021 22:09:17 »

Why in the SDO satellite photo, the Moon has a clear (not defocused) outline, given ...the “fact” that the Sun is officially 400 times farther than the Moon?

It has to do with the diameter of the telescope, the resolution of the imager, and the distance to the Moon & Sun.
- SDO is in geosynchronous orbit around the Earth, so the Moon is about 300,000km away±10%, and the Sun is about 150 million km away±1%
- From photos of the orbiter, it looks like the telescope has a diameter of about 300mm (I couldn't find a written figure)
- The shortest wavelength it can observe is 9.4nm
- So the diffraction-limited resolution is 0.01 arc-seconds for the shortest UV wavelength (and worse for longer wavelengths)
- The imager is 4k x 4k pixels, covering a width of about 40 arc-seconds, so the imager resolution is also around 0.01 arc-seconds
- The disk of the Sun is 32 arc-seconds across, from the Earth's distance
- The disk of the Moon is also 32 arc-seconds across, from the Earth's distance
- So a telescope focused on the Sun will have a fuzziness of 1 pixel when viewing the Sun
- So a telescope focused on the Sun will have a fuzziness of 1 pixel when viewing the Moon
- So the image of the Moon is as sharp as the image of the Sun, even though the telescope is focused on the Sun

In practice, astronomical telescopes are focused "at infinity", which works well for both planets and stars.
- Even though the planet:star ratio of distances is even more extreme than the Moon:Sun distance

See: https://en.wikipedia.org/wiki/Solar_Dynamics_Observatory
https://en.wikipedia.org/wiki/Diffraction-limited_system#/media/File:Diffraction_limit_diameter_vs_angular_resolution.svg

113

Technology / Re: The most advanced space technology you ever heard about

« on: 02/01/2021 21:17:42 »

(The far side of the Moon is) a black-out area for measurement

I'm afraid that as soon as we go someplace, we take sources of interference with us.

The Chinese have a rover on the far side of the Moon. So they have a relay satellite orbiting the Lunar L2 point (but with a radius big enough so that it can always be seen from Earth, around the sides of the Moon).

See: https://en.wikipedia.org/wiki/List_of_objects_at_Lagrange_points#Earth%E2%80%93Moon_Lagrange_points

114

Physiology & Medicine / Re: What causes young people to die in their sleep?

« on: 01/01/2021 21:46:54 »

Undiagnosed heart problems?

115

New Theories / Re: Alternate take on Fermats Last Theorem

« on: 01/01/2021 21:40:46 »

What made Fermat's last theorem so hard is that it demands "a solution in integers".
- This demanded breakthroughs in linking previous separate areas of mathematics

If they merely wanted solutions on a 10-digit calculator, all it needs is a 10-digit calculator (and a lot of patience).
- Modern computers usually use 64-bit floating-point numbers, which are accurate enough to prove that the 10-digit calculator is wrong

116

Cells, Microbes & Viruses / Re: What are the best answers for Corona statistics?

« on: 01/01/2021 21:33:33 »

I understand that the Chinese vaccine is also being trialed in Brazil.
Unlike China, the Brazilian President Bolsinaro followed Trump's pro-virus policy, so Brazil has plenty of victims to test the effectiveness of the vaccine.

Still waiting for detailed results, but early hints are that it appears less effective than some of the other vaccine candidates.
See, for example: https://www.voanews.com/covid-19-pandemic/brazilian-researchers-say-chinese-made-covid-19-vaccine-effective

117

Just Chat! / Re: Predictions?

« on: 01/01/2021 21:14:24 »

Famine within plague

In the days when many cities were captured by siege, these two things often went together.
- Cut off from food supplies, there was a famine in the city
- With no fresh food, vitamin intake was too low, and diseases like scurvy took over
- So it may not have been an infectious plague (eg virus or bacterium), but it may have been a dietary problem

Of course, it could also go the other way - even without a siege, a plague could decimate the rural workforce, producing a famine.

118

New Theories / Re: How much information can we get from a single photon?

« on: 01/01/2021 21:05:05 »

Is it possible to distinguish if a photon with a particular frequency is produced by a stand still source with that frequency or a moving source with higher/lower frequency?

It is possible to correct for Doppler shift if you know the relative velocity of the emitter and receiver. If you are talking about a spaceship and the control center, that relative velocity will be known fairly accurately.

You would not try and send a message on a single photon - it could hit a speck of dust and be lost.
- If the laser beam from the transmitter is 100km in diameter when it reaches the receiver, and the receiver is using a telescope 1m across to receive the signal, you will miss almost all the photons.
- The good thing about photons is that they are relatively easy to produce in large quantities.

From a communications viewpoint, typically, you would send a message with:
- A certain bandwidth. The center of this bandwidth tells you the Doppler shift offset
- A certain timing. There is a clock signal embedded in the signal that allows you to extract a synchronization signal from what is received. Synchronous reception allows you to carry more data
- A certain number of bits per symbol. This is selected based on the noise in the signal (if the Signal-to-Noise ratio is worse, you send fewer bits per symbol).
- A certain duration: The more information you need to transmit, the longer the duration
- A certain schedule: One receiver has to monitor many transmitters. You want to transmit at the time you know the receiving telescope will be pointed at you (and not on the other side of the planet, or obscured by the Moon, for example)
- Enough photons so that you will on averagereceive more than one photon for each symbol you are transmitting
- For those cases where you receive 0 photons for some symbols, you add an error-correcting code, which allows you to reconstruct the missing symbols (providing there aren't too many of them). Normally the most advanced error correcting codes are tried first in space systems, as they have more challenging error conditions than most terrestrial applications (except maybe for spies communicating covertly).
- These days, when computer memory is relatively cheap, you store the data until you have confirmation that the signal has been received before deleting it. You retransmit the segments that could not be reconstructed (because too many symbols were lost for them to be recovered by the error-correcting code)

119

That CAN'T be true! / Re: I don’t understand physics: does anyone understand physics these days?

« on: 01/01/2021 00:39:24 »

...Gravity Waves, had been wrongly wired up

It is true that LIGO (USA), VIRGO(Italy) and KAGRA (built by a team in Japan) are continually straining to extract a Gravitational Wave signal from the noise.

But the Nobel Committee awarded a prize in 1993 for astronomical evidence of Gravitational Waves from a binary pulsar.
- This was well before the first gravitational wave detection by LIGO, in 2015
- This pulsar method doesn't require detection of subtle vibrations smaller than the diameter of a proton.
See: https://en.wikipedia.org/wiki/Hulse%E2%80%93Taylor_binary

In reality, the generation of Gravitational Waves in Spacetime from accelerating masses is no more surprising than:
- generation of Electromagnetic Waves from accelerating charges in a wire (eg radio, TV and cell phones)
- generation of Water Waves from a stone dropped in a pond (accelerating water molecules)

120

That CAN'T be true! / Re: I don’t understand physics: does anyone understand physics these days?

« on: 01/01/2021 00:27:30 »

Wouldn't that be a huge embarrassment to Science?  Could it ever be admitted?

https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment#Most_famous_%22failed%22_experiment
- This "failed" experiment was one of the inputs to Einstein's theory of relativity
- What you have missed is that scientists actually like finding errors in previous theories, as it gets them research grants and highly-cited papers (eg anomalous rotation of galaxies)
- and the bigger the error they discover, the more likely they are to receive a Nobel prize (eg the accelerating expansion of the universe)
- The Nobel committee tends to be very conservative, so if an area receives a Nobel Prize, it has been fairly convincingly demonstrated (eg gravitational waves)

For failures of a different kind, see: https://en.wikipedia.org/wiki/Strategic_Defense_Initiative#Controversy_and_criticism

In fact, there are Wikipedia pages listing things that just seem wrong (or at least incomplete).
- One of them is physics beyond the Standard Model (which many physicists today link to identifying the nature of Dark Matter)
- In contrast to this, the Higgs Boson was predicted as part of the current standard model, and some of it's characteristics fairly well predicted (but it's mass was highly uncertain)
- If the Higgs were not real, you would find several new entries on the following page:
See: https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics

It's not the only field with unsolved problems:
https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_mathematics
https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_chemistry
https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_biology
https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_neuroscience