Like I said in the last video we are about to enter the 1900s
But there's one more huge discovery that occurred at the very end of the 1800s that we really cannot ignore
When it comes to the three subatomic particles which make up an atom they were each discovered years apart our understanding of the atom
Definitely evolved over time and did not come all at once the first one that was proven to exist
Which is also the smallest of the three is the electron the concept the electron was first theorized in 1838 by philosopher Richard Lamy
He I pathi sized a quantity of electric charge which could not be subdivided and would explain certain properties of an atom
It was finally in 1897 that physicist JJ Thompson proved these were in fact particles
He was running experiments with cathode rays and actually ran quite a few
But the main one was testing to see whether these rays would deflect due to an electric field
Cathode rays or beams of electrons emitted from one side of a vacuum tube, of course
This was not known back then as physicists thought this beam may in fact be a wave since the exhibited properties unique to a wave
Whereas others thought the Rays were in fact particles
JJ Thompson's experiment involved
exposing the beam to an electric field and he found that the beam bent towards the positive side of the field which proved without a
doubt that these rays are made of negatively charged particles the
Same physicist who discovered the electron proposed one of several models of the atom known as the plum pudding model in 1904
Just a couple years after his discovery
where electrons made up a very small portion of the atom and were scattered throughout like plums and pudding it would not be long until
This was superseded though a few years later starting in 1908
The physicist Rutherford was interested in determining the true structure of an atom which he thought was more complex than the plum pudding model predicted
What he ended up doing was firing charged alpha particles through gold foil, which most of his learning chemistry as the Rutherford gold foil experiment
He said that these gold atoms were like the plum pudding model
The particles would go straight through and this is sort of what happened
But after more testing he found that certain particles were being reflected back, which should have been
Impossible this imply that there was a much stronger electrostatic force than previously predicted
Meaning the atoms positive charge was very concentrated in a small volume in
1913 he published a paper declaring the existence of what he called a nucleus which contained a positive charge
Then just a few years later also through experiments involving firing alpha particles this time at a nitrogen atom
Rutherford found that positive charges came in single units he named this unit the proton
Same charge as an electron but nearly two thousand times heavier
With that we had a much better understanding of the atom
However, the puzzle was not complete and it would be more than a decade until the neutron was discovered, which I'll come back to soon
now, like I said in the last video our understanding of various extremes would soon be greatly improved upon when it comes to extremes like
The very fast very cold, very small, etc
Strange things happen often completely counterintuitive to what we know of from the macroscopic world on a day-to-day basis
We experience a range of temperatures or a range of speeds. For example
But nothing remotely close to the physical limit of these parameters where these odd properties take place
The first that really popped up in this century dealt with the very fast, which brings us to iron Stein's theory of special relativity
Einstein theorized something that like I said is extremely counterintuitive to what we would think about ordinary everyday objects
He said that the speed of light in a vacuum is the same for all observers regardless of the motion of a light source
Imagine that you're observing someone standing on a moving train
Maybe that train that's moving 50 km/h and they throw a ball at 30 km/h if you both had radar guns
What would they read? Well, the person on the train would read the ball is moving at 30 km/h, that's how fast they threw it
But the person on the ground would see 80 km/h as the Train speed would be a factor in terms of relative motion
So you would not agree on the speed of the ball and this is perfectly normal. This should not be of any surprise
but when it comes to light
We always agree on the speed
That train could be going a billion kilometres per hour
If you both had a hypothetical radar gun to measure light they would both read the exact same speed the speed of light
One consequence of this is time dilation
which says that time takes slower for moving objects compared to those that are standing still as
In clocks tick slower and people age slower when they're moving
This is what makes it possible for a twin to go on a high-speed rocket and come back younger than the other
This has even been verified by putting very precise atomic clocks in orbit and having them come back slightly off from another here on earth
In fact the equation for this as a denominator that approaches zero as the moving person approaches the speed of light
So in theory if you got in a rocket that could go
Extremely close to the speed of light and set a timer to maybe one day when you return to Earth
millions billions or maybe
trillions of years would have gone by depending on how fast you went and you
Would have aged just one day and you would think one day I'd be gone by you
May be wondering what would happen
If you could exceed the speed of light but special relativity says this is a universal speed limit and therefore nothing can exceed it
Now after special relativity Einstein attempted to extend this theory to a more general form
Which would be known as general relativity acknowledged by some of the most beautiful physical theory currently in existence
Well Einstein was working on this theory. He of course ran into constant problems one day. He accepted an invitation to speak at a university
Where he would explain what he was working on
he was explaining the problem at hand to the audience and one person sitting amongst the group of people was David Hilbert's one of the
greatest mathematicians of all time and while observing everything that I'm Stein is saying
Hilbert thinks that he can figure out this theory better than Einstein can and from there
It was a race between Hilbert and Einstein for who would be the one to complete one of the greatest theories of all time
Now by pretty much anyone standards Einstein was good at math, but he was no mathematician
in fact
He often needed help from mathematicians to complete his theories and at this point general activity was a problem of pure
Mathematics and he was up against a mathematician in the end Hilbert Einstein completed the theory at just about the same time
But since so many of the foundations were started by Einstein
Hilbert did not take any of the credit and this became Einstein's theory of general relativity general
relativity is something you would not learn about until likely your last year in undergrad as a physics major or maybe grad school has it's
Much more advanced than special relativity when we use Newton's laws to analyze the motion of very large objects such as planets and stars
Small errors actually occur which general relativity finally accounted for hundreds of years. Later
Basically generality explains gravity and how mass actually bends space and time
the orbit of mercury for example has an odd pattern compared to other planets that cannot be explained by any
Theories until general relativity came along and explain these slight alterations
The reason we need general relativity is that mercury is close enough to the Sun shows that the warping of space affected its orbit
Whereas other plants were far enough away for Newtonian physics to give accurate predictions
General activity helps us understand black holes and a predicted gravitational ways
which were finally observed just a couple of years ago and one three physicists the Nobel Prize in
2017
Now that we've covered the very fast and the very large what happens when you take a metal to a very cold temperature
Well when you do this
It becomes a superconductor and in 1911 one scientist managed to cool mercury to four point one nine Kelvin or about minus
269 degrees Celsius what he observed was that the electrical resistance of the object disappeared entirely
Where electrons in the metal were completely free to move and it was a superconductor
Superconductors exhibit interesting property says that they expel magnetic fields and make levitation possible
This is used in maglev trains that float above the ground for example
Now if we achieve these at normal temperatures we can use them for a wide range of applications one being an electric power transmission
A lot of electric power is lost due to friction as it's transmitted to our homes with superconductors having no resistance
We would minimize those losses and therefore reduce costs for everyone
Superconductors apply to particle detectors faster electronics and high frequency electrical systems as well at the moment
The applications are limited due to the needed temperature for superconducting properties to occur in
1986 the first ever high-temperature superconductor was discovered by two researchers who were awarded the Nobel Prize for their work
This quote high temperature was only around 130 Kelvin or minus 135 degrees Celsius, though
The highest temperature superconductor as of a few years ago is negative 70 degrees Celsius discovered in 2015
but we hope room-temperature superconductors will be here in the future and
Now that we've gone over metals what happens when a liquid gets very cool
You may think that's a trick question as a liquid will just become a solid but take helium
for example at
Normal pressures once a liquid this will remain a liquid all the way down to absolute zero the cold is something can possibly get in
1937 a temperature of near absolute zero was achieved for a sample of liquefied helium and the first superfluid was served
Superfluids happen when liquids get very cold
And these also exhibits strange properties for one superfluids have no viscosity and this is basically a measure of a liquid resistance to deformation
Which you can kind of think of as the thickness of the liquid since super fluids have none
When stirred it will form a vortex that would constantly rotate imagine stirring your drink then seeing the liquid never stop turning once you stopped
Also when put in a container, it will creep up the sides and along the outside forming a droplet at the bottom
Now going back real quick in nineteen eleven physicist charles wilson was hiking ben
Nevis the highest peak in scotland where he got to see a mountain Spectre
This is an optical event that happens when sun shines from behind an observer looking out onto some peak or ridge of fog
When this occurs the observers head is usually surrounded by coloured rings of light Wilson
I've been studying meteorology and cloud formations for some time now
But became motivated to then take a crack at creating clouds with a machine this then led to the invention of the cloud chamber
But well, this one accomplished probably is not what you'd expect and is definitely not what Wilson had anticipated at first
These cloud chambers that were filled with water vapor to form clouds of droplets actually made it very easy to see trails of ionized gas
Particles these trails occur when charged particles such as alpha or beta particles like we saw earlier within radioactive decay
Interact with the gas in the chamber these events are typically not detectable by the human eye
But the cloud chamber would change that what was meant to be a chamber to create clouds really became a particle detector
This invention went on to accelerate the study of particle physics around 30 years until it was superseded by the bubble chamber
So take the study of cosmic rays as an example over 100 years ago physicists assumed radioactive rocks in the Earth's crust
Released high-energy particles iwould ionized gases in the air and give it a charge which in fact we were able to measure
We were not sure about the source if this source of radioactive rocks was accurate, then the ionization should be reduced with altitude
In 1910 physicist Theodore wolf took an electroscope to the top of the Eiffel Tower
He found that levels of radiation were higher at the top than the base the exact opposite of what should have happened
and in 1912 Victor has carried an electroscope to an altitude of
5000 300 meters in a balloon flight and again found a huge increase in the rate of ionization
From this finding he concluded that this radiation was not coming from earth
But instead from space
The Sun being a source was ruled out when he made another balloon trip during a solar eclipse and still measured a rise in radiation
therefore must be coming from somewhere else in space and this radiation came known as cosmic rays a
Source of cosmic rays would be like a supernova or the explosion of a star ejecting
Most of its mass these travel through space at very high speeds hit Earth's atmosphere every single minute of every single day
These are made up of mostly protons and alpha particles or the nucleus of helium
But when they hit Earth's atmosphere, they can produce a cascade of lighter particles raining down things like x-rays protons electrons and muons
The muon is similar to an electron with the same negative charge but is about 200 times heavier
These were discovered in 1936 during the study of cosmic radiation and were officially confirmed by using a cloud chamber experiment
Muons also have an average lifetime of 2.2 microseconds
Which means that there should only be so many of these that even reach the surface of the earth
However, in the early 40s scientists measured over ten times more muons reaching a certain location on earth than expected
This was essentially the first time that time dilation due to Einstein's special theory of relativity was proven to be correct
Time does in fact tick slower for objects moving at very fast speeds
cloud chambers
bubble chambers which came about in the 50s and are very similar to cloud chambers the discovery of cosmic rays and the positron which I
Didn't talk about but was discovered through the use of a cloud chamber all ended up winning these various physicists a Nobel Prize
Moving on in 1927 a man named George Thompson the son of the person who discovered the electron about three decades earlier
Perform an experiment that would change how we think about the electron what he did was perform the double slit experiment
But instead of light he used electrons now
You would think that if you shot electrons through two slits, you would see two groups of dots one behind each slit
This is what would happen. If you perform this on a macro scale with like marbles, let's say but this amazingly was not observed
What he found is that same interference pattern appeared on the screen like it did with light
He conclude that the particle his father discovered was not just a particle
But also a wave it had properties of each and this is now known as wave particle duality
Similarly we've also discovered that light exhibits the same dual nature
And first we typically learned that light is a wave but it can also exhibit particle-like properties such as when light ejects electrons from metal
This is known as the photoelectric effect, which was eventually used to create solar cells
What may surprise you is the fact that Einstein is known for some very famous theories
However, the one Nobel Prize he won was worth discovery of the law of the photoelectric effect
He wasn't the first to observe the photoelectric effect
But did publish papers that gave a more detailed explanation of the nature of light and the photoelectric effect itself
next up in 1931 experiments were done in which samples of boron or beryllium
Were hit by alpha particles and what was discovered was an unusual type of radiation that was not influenced by an electric field
It was assumed to be gamma radiation
But both rutherford and a physicist named James Chadwick did not believe this
The following year Chadwick ran some experiments to show that this radiation consisted of uncharged particles
With about the same mass as a proton
We now call these particles neutrons and finally the three subatomic particles of the atom had all been discovered
Chadwick was awarded the Nobel Prize in 1935 for this discovery, but what's more interesting is what happened next in?
1938 just a couple years after the discovery of the neutron something else was discovered that would revolutionize nuclear physics
Chemists at Ojai began bombarding uranium atoms with neutrons as a result
One thing he found in the sample was barium if we look at a periodic table barium and uranium are quite far apart
So no one knew why this was happening a normal radioactive decay
You may have a uranium nucleus in which an alpha particle is released
Thus creating a thorium nucleus in the process do the loss of two protons and two neutrons
You can see here how thorium is atomic number is just to less than uranium's
The small change is what we're familiar with so you can see why it was odd to see barium in a sample
Well, two physicists determine that in this case the nucleus the uranium atom just split in two which is why an element with a much
Different atomic number was a served. This became known as nuclear fission
Now when nuclear fission takes place and the nucleus splits
Yes, it leaves behind two other nuclei
But it can also release neutrons in the process which can then go on to split more atoms which release more neutrons and a chain
reaction occurs
Which releases a ton of energy this finding is what started a race to create an atomic bomb where this chain reaction would occur in
1942 the United States put full focus into creating these atomic weapons and control the nuclear fission process
This became known as the Manhattan Project and in 1945 the strikes on Hiroshima and Nagasaki
Showed just how powerful nuclear fission could be
Nuclear physics is not all about weapons though as nuclear fission is what takes place with the nuclear reactors
they talked about earlier that are what power a good percentage of the world in a way that is relatively cheap and yields very little
pollution
Now for a while
We were not sure whether electrons protons and neutrons were elementary particles or particles that are not made up of anything else in
1964 physicists proposed that protons and neutrons were in fact made up of something else even smaller
These extremely small particles became known as quarks. It was until four years later
1968 that experiments were done at the Stanford Linear Accelerator in which electrons were fired at protons electrons
are much smaller in size and they observe that they bounced off the proton in such a way that could not be explained if the
protons for just one ball of charge
They conclude they must be made of something else
And now these quarks help us understand much more about the atoms within our universe
It was also assumed that the smallest charge possible was that of an electron
But we now know that quarks have an even smaller charge
Those quarks then add up to the charge of the respective particle. They make up
Now we've talked about general relativity which encompasses gravity and the very large that we've also talked about atoms and the very small
But at the moment, there's no theory that relates the very small to the very large or a theory of everything
Currently we cannot use quantum mechanics a branch of physics that deals with subatomic particles to explain gravity
One of the most promising areas of research that may accomplish. This is string theory
String theory hypothesizes that these tiny little strings within electrons protons quarks, etc
Make up our universe and propagate through space and interact to one another
string theory predicts that there are at least 10 dimensions to our universe with some theories such as bosonic string theory saying space-time is
26 dimensional and although Heim Stein's theory of general relativity explains gravity
It cannot explain what happens at the center of a black hole currently
string theory may help accomplish this by explaining gravity from a quantum perspective and
On the topic of black holes, it had been assumed for a while
That black holes should always be increasing in size since material could only be consumed nothing in theory can escape a black hole?
however
In 1974 Stephen Hawking published a paper called black hole explosions in which he discussed a new union of quantum mechanics and general relativity
in
This he said black holes should actually release a certain type of radiation causing them to lose mass. This radiation became known as Hawking radiation
The common explanation for this is that pairs of particles including both matter and antimatter
Exist throughout our universe appearing and then destroying each other constantly
But around a black hole occasionally one particle will be lost to the event horizon while the other escapes
The particle that escapes takes some extra energy with it
which is given up by the black hole and turned causing the black hole to slowly lose its mass and
Lastly in the second half of the 1960's
Scientists began working on developing the standard model which would explain all the forces and matter that exists in the universe
The standard model currently contains various elementary particles broken up into various classes
the standard model also explains three of the four forces of nature as
You can probably guess the one that it cannot currently explain is gravity
But in 2012 a new particle was discovered that would be added to this model this particle explained the origin of mass of subatomic
particles and was confirmed by experiments at CERN's Large Hadron Collider
This particle was coined. The Higgs boson named after Peter Higgs who predicted such a particle several decades earlier and
With that we have officially gone through the entire history of physics besides maybe a few extra things here and there
Yes, there's of course plenty more that I wanted to go over but due to time
I'm gonna end that video here if you enjoyed be sure to LIKE and subscribe
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