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Hi everybody.
First of all, I want to welcome all the new subscribers; we are almost a hundred thousand
now, which is super-exciting.
This week, I have something for your intellectual entertainment; I want to tell you about some
really big experiments that physicists dream of.
Before I get to the futuristic ideas that physicists have, let me for reference first
tell you about the currently biggest experiment in operation, that is the Large Hadron Collider,
or LHC for short.
Well, actually the LHC is currently on pause for an upgrade, but it is scheduled to be
running again in May 2021.
The LHC accelerates protons in a circular tunnel that is 27 kilometer long.
Accelerating the protons requires powerful magnets that, to function properly, have to
be cooled to only a few degrees above absolute zero.
With this, the LHC reaches collision energies of about 14 Tera Electron Volt, or TeV.
Unless you are a particle physicist, this unit of energy probably does not tell you
much.
It helps to know that the collision energy is roughly speaking inversely proportional
to the distances you can test.
So, with higher collision energies, you can test smaller structures.
That’s why particle physicists build bigger colliders.
The fourteen TeV that the LHC produces correspond to about ten to the minus nineteen meters.
For comparison, the typical size of an atom is ten to the minus ten meters, and a proton
roughly has a size of ten to the minus fifteen meters.
So, the LHC tests structures a thousand times smaller than the diameter of a proton.
As you may have read in the news recently, CERN announced that particle physicists want
a bigger collider.
The new machine, called the “Future Circular Collider” is supposed to have a tunnel that’s
one-hundred kilometers long and it should ultimately reach one-hundred TeV collision
energy, so that’s about six times as much as what the LHC can do.
What do they want to do with the bigger collider?
That’s a very good question, thanks for asking.
They want to measure more precisely some properties of some particles.
What it the use given that these particles live some microseconds on the outside?
Nothing, really, but it keeps particle physicists employed.
The former Chief Scientific Advisor of the British government, Prof Sir David King, commented
on the new collider plans in a BBC interview: “We have to draw a line somewhere, otherwise
we end up with a collider that is so large that it goes around the equator.
And if it doesn't end there perhaps there will be a request for one that goes to the
Moon and back.”
Particle physicists don’t currently have plans for an accelerator around the equator,
but some of them proposed we could place a collider with one-thousand-nine-hundred kilometer
circumference in the gulf of Mexico.
What for?
Well, you could reach higher collision energies.
However, even particle physicists agree that a collider the size of the Milky Ways is not
realistic.
That’s because, as the particle physicist James Beachman explained in an Interview with
Gizmodo, unfortunately even interstellar space, with a temperature of about 3 degrees above
absolute zero, is still too warm for the magnets.
This means you’d need a huge amount of Helium to cool the magnets.
And where would you get this?
But even a collider around the equator would be a technological challenge.
Not only because of the differences in altitude, also because the diameter of Earth pulses
with a period of about 21 minutes.
That’s one of the fundamental vibrational modes of the Earth and, by the way, more evidence
that the earth is not flat.
The fundamental vibrational modes get constantly excited through earthquakes.
But, as a lot of physicists have noticed, this is a problem which you would not have
--- on the moon.
The moon has very little seismic activity, and there’s also no life crawling around
on it, so, except for the occasional asteroid impact, it’s very quiet there.
Better still, the moon has no atmosphere which can cloud up the view of the night sky.
Which is why physicists have long dreamed of putting a radio telescope on the far side
of the moon.
Such a telescope would be exciting because it could measure signals from the “dark
ages” of the early universe.
This period has so-far been studied very little due to lack of data.
The dark ages begin after the emission of the cosmic microwave background but before
the formation of the first stars, and they could tell us much about both about the behavior
of normal matter and that of dark matter.
The dark ages, luckily, were not entirely dark, just very, very dim.
That’s because back then the universe was filled mostly by lots of hydrogen atoms.
If these bump into each other, they can emit light at a very specific wavelength, 21 cm.
This wavelength then stretches with the expansion of the universe and should be measureable
to day with radio telescopes.
Physicists call this “21 centimeter astronomy” and a few telescopes are already looking out
for this signal from the dark ages.
But the signal is very weak and hard to measure.
Putting a telescope on the moon would certainly help.
This is not the only experiment that physicist would like to put on the moon, if we’d just
let them.
Just in February this year, for example, a proposal appeared to put a neutrino source
on the moon and send a beam of neutrinos from there to earth.
This would allow physicists to better study what happens to neutrinos as they travel.
This information could be interesting because we know that neutrinos can “oscillate”
between different types as they travel – for example an electron-neutrino can oscillate
into a muon-neutrino – but there are some oddities in the existing measurements that
could mean we are missing something.
And only a few weeks ago, some physicists proposed to put a gravitational wave interferometer
on the moon, though this idea was originally proposed already in the 1990s.
Again the reason is that the moon is far less noisy than our densely populated and seismically
active planet.
The downside is, well, there are no people on the moon to actually build the machine.
That’s why I am more excited about another proposal that was put forward some years ago
by two physicists from Harvard University.
By the way, as always you find references in the information below the video.
These guys suggested that to better measure gravitational waves, we could leave a trail
of atomic clocks behind us on our annual path around the sun.
When a gravitational wave passes through the solar system, the time that it takes signals
to travel between the atomic clocks and earth slightly changes.
The cool thing about it is that this would allow physicists to detect gravitational waves
with much longer wavelengths than what is possible with interferometers on earth or
on the moon.
Gravitational waves with such long wavelengths should be created in the collisions of supermassive
black holes and therefore could tell us something about what goes on in galactic cores.
These experiments have in common that they would be great to have, if you are a physicist.
They also have in common that they are big.
And since they are big, they are expensive, which means chances are slim any of those
will ever become reality.
Unfortunately, ignoring economic reality is common for physicists.
Instead of thinking about ways to make experiments smaller, easier to handle, and cheaper to
produce, their vision is to do the same thing again, just bigger.
But, well, bigger isn’t always better.
Thanks for watching, see you next week.