A Crash Course In Particle Physics (1 of 2)

00:13:01
https://www.youtube.com/watch?v=HVxBdMxgVX0

Summary

TLDRThe video delves into the evolution of scientific understanding from the concept of indivisible atoms to the discovery of subatomic particles like electrons, protons, and neutrons. The journey begins with 19th-century scientists believing in over 80 elements and atoms as indivisible spheres. J.J. Thomson's experimentation led to the discovery of the electron, altering the notion of the atom. Rutherford's gold foil experiment revealed the electron's structure, showing atoms as mostly empty space with a dense nucleus. Further advancements in the 20th century extended to cosmic rays uncovering new particles. Eventually, Murray Gell-Mann's identification of quarks as fundamental building blocks simplified the complexity of the particle zoo. The role of forces, the agents of change in the universe, is also highlighted, emphasizing their necessity in particle interactions and universal dynamics, exemplified by the cutting-edge experiments conducted at CERN.

Takeaways

  • 🔬 Particle accelerators aid in understanding matter's building blocks.
  • ⚛ Atoms are not indivisible; electrons are one of many particles.
  • 💡 Rutherford unveiled the nucleus, altering atomic models.
  • 🌌 Cosmic rays discovered particles beyond protons, neutrons, and electrons.
  • 🔗 Quarks simplified the complexity of numerous particles.
  • ⚡ Forces drive changes and interactions throughout the universe.
  • 🏛 CERN is pivotal in researching the fundamental forces and particles.
  • 📜 History of science shows evolution from elements to subatomic particles.
  • 🌀 Quantum mechanics refines our understanding of atomic structure.
  • 🌠 Forces play a pivotal role in both cosmic and subatomic scales.

Timeline

  • 00:00:00 - 00:05:00

    In the early days of understanding the natural world, people believed there were over 80 elements that made up everything, organized in the periodic table. However, scientists like JJ Thomson discovered that atoms, thought to be indivisible, contained smaller particles. Utilizing a form of particle accelerator, Thomson identified electrons as subatomic particles, which reshaped the fundamental concept of the atom. His discovery led to the realization that atoms were not solid spheres but had internal structures, likened to a muffin with embedded electrons. This pivotal moment in science marked the beginning of atomic substructure exploration.

  • 00:05:00 - 00:13:01

    Ernest Rutherford advanced the study of atomic structure by using radioactive decay to investigate matter, leading to the understanding of the atomic nucleus. His experiments showed that most of the atom is empty space, with a dense nucleus composed of protons and neutrons. Rutherford's findings demonstrated that the atom was mostly space, upending prior models, and the discovery of neutrons by James Chadwick further refined the atomic model. However, cosmic rays and subsequent experiments revealed more particles than protons, neutrons, and electrons, leading to the development of particle physics laboratories and accelerators. This proliferation of particles was later categorized into a simple system by Murray Gell-Mann, who introduced the concept of quarks, redefining the understanding of particle physics. Through symmetries and the quark model, a more elegant understanding of the forces in nature was achieved.

Mind Map

Video Q&A

  • What did scientists believe about elements in the 19th century?

    Scientists thought that everything on Earth was made of just over 80 elements, arranged in a periodic table by Dmitri Mendeleev.

  • Who discovered the electron and how?

    J.J. Thomson discovered the electron using a particle accelerator, finding particles much lighter than hydrogen atoms.

  • How did Rutherford contribute to atomic theory?

    Ernest Rutherford discovered the atomic nucleus by firing alpha particles at gold foil, showing that most of the atom is empty space.

  • What are the fundamental particles discovered by 1932?

    By 1932, scientists identified the electron, proton, and neutron as fundamental particles.

  • What significant discovery was made using cosmic rays?

    Cosmic rays led to the discovery of new particles that couldn't be explained by known fundamental particles like protons and electrons.

  • What is the significance of quarks in particle physics?

    Quarks, identified by physicist Murray Gell-Mann, were found to be the basic building blocks of protons, neutrons, and other particles.

  • How do forces relate to particles and matter?

    Forces are crucial because they cause interactions and changes in the universe, affecting everything from atomic structures to cosmic events.

View more video summaries

Get instant access to free YouTube video summaries powered by AI!
Subtitles
en
Auto Scroll:
  • 00:00:00
    [Music]
  • 00:00:24
    the world seems almost infinitely
  • 00:00:26
    complicated made up of thousands if not
  • 00:00:29
    Millions of different
  • 00:00:34
    materials throughout history people have
  • 00:00:36
    tried to collect categorize and analyze
  • 00:00:38
    them to find some underlying pattern
  • 00:00:41
    that would help simplify this seemingly
  • 00:00:44
    incredibly complicated world now at the
  • 00:00:47
    dawn of the 21st century we've made some
  • 00:00:50
    progress to achieving that long yearned
  • 00:00:52
    for
  • 00:00:53
    simplification with the use of particle
  • 00:00:55
    accelerators we are starting to
  • 00:00:58
    understand the nature of the world
  • 00:00:59
    around us
  • 00:01:03
    these machines have revealed a whole
  • 00:01:04
    array of particles which we believe may
  • 00:01:08
    be the fundamental building blocks of
  • 00:01:11
    matter but back in the 19th century
  • 00:01:14
    scientists thought that everything on
  • 00:01:16
    Earth was made of just over 80 elements
  • 00:01:20
    these elements were famously arranged in
  • 00:01:21
    a periodic table by Demitri
  • 00:01:25
    Mev at the time it was thought the
  • 00:01:27
    elements were made of indivisible
  • 00:01:29
    spheres called
  • 00:01:32
    [Music]
  • 00:01:35
    atoms but each of the elements behaved
  • 00:01:37
    in a different way did that mean that
  • 00:01:40
    there were 80 different kinds of atom
  • 00:01:42
    and if so what made them
  • 00:01:45
    different were they different shapes or
  • 00:01:48
    sizes or maybe the atoms were divisible
  • 00:01:52
    maybe they were built of even smaller
  • 00:01:54
    objects
  • 00:01:55
    [Music]
  • 00:02:00
    it was here in Cambridge that the first
  • 00:02:02
    clear evidence for smaller objects
  • 00:02:04
    inside the atom was found many of the
  • 00:02:07
    Great scientists of History walked these
  • 00:02:09
    streets and one of the greatest was JJ
  • 00:02:12
    Thompson who became the director of this
  • 00:02:15
    the old Cavendish
  • 00:02:20
    laboratory in 1896 Thompson had just got
  • 00:02:23
    his hands on this new piece of Kit now
  • 00:02:26
    it's essentially a particle accelerator
  • 00:02:28
    when this plate is heated particles are
  • 00:02:30
    emitted they're accelerated by these
  • 00:02:33
    electrodes they pass through these two
  • 00:02:35
    plates across which you can apply a
  • 00:02:37
    voltage and they hit the end of the bulb
  • 00:02:40
    here on a screen which glows so you can
  • 00:02:42
    see the beam now this is a modern
  • 00:02:45
    version of Thompson's apparatus again
  • 00:02:47
    we've got the particle accelerator and
  • 00:02:49
    there's a screen in there so you can see
  • 00:02:50
    the beam glow what Thompson did was he
  • 00:02:53
    varied the voltage across the plates and
  • 00:02:56
    he measured the amount of bending as the
  • 00:02:58
    voltage changed that allows you to
  • 00:03:00
    deduce the mass of the particles in the
  • 00:03:03
    beams now the lightest known particle in
  • 00:03:05
    Thompson's day was the hydrogen atom but
  • 00:03:08
    Thompson found from these measurements
  • 00:03:10
    that the particles in this beam are
  • 00:03:13
    almost 2,000 times lighter than hydrogen
  • 00:03:16
    atoms Thompson had discovered the first
  • 00:03:18
    subatomic particle the
  • 00:03:24
    electron the uh electron owes its
  • 00:03:27
    practicality utility to its
  • 00:03:31
    smallness it might apparently
  • 00:03:34
    Shakespeare say my use is great because
  • 00:03:37
    I am so
  • 00:03:39
    small the electron was the first
  • 00:03:43
    discovery of a fundamental particle and
  • 00:03:45
    it is interesting to realize that more
  • 00:03:47
    than a hundred years later the electron
  • 00:03:49
    is still to the best measurements we can
  • 00:03:51
    do today a fundamental letter of
  • 00:03:53
    Nature's alphabet we can use electrons
  • 00:03:56
    as ways to probe materials and look at
  • 00:03:58
    the structure in elect on microscopes or
  • 00:04:00
    in big machines like this accelerator
  • 00:04:02
    behind me pretty much all of of
  • 00:04:04
    everything we do in the in the 21st
  • 00:04:06
    century depends on understanding the
  • 00:04:08
    properties of
  • 00:04:14
    electrons Thomson had discovered that
  • 00:04:16
    the atom is not the fundamental building
  • 00:04:18
    block of matter there are smaller
  • 00:04:20
    objects inside so atoms could no longer
  • 00:04:22
    be thought of as hard indivisible
  • 00:04:25
    spheres but how do the electrons fit
  • 00:04:27
    inside the atom Thompson suggested that
  • 00:04:30
    the atom was something like this muffin
  • 00:04:32
    with the negatively charged electrons
  • 00:04:34
    embedded in a positive
  • 00:04:37
    body it would be student of Thompson
  • 00:04:40
    that proved him
  • 00:04:41
    [Music]
  • 00:04:47
    wrong the mystery of how the electrons
  • 00:04:49
    fitted inside the atom was eventually
  • 00:04:52
    solved here in Manchester in this
  • 00:04:54
    building in 1911 by Ernest
  • 00:04:58
    Rutherford Rutherford was in my opinion
  • 00:05:01
    one of the first proper particle
  • 00:05:03
    physicists because he used beams of
  • 00:05:06
    particles as projectiles to explore the
  • 00:05:09
    structure of matter now of course In
  • 00:05:11
    Rutherford's day there was no such thing
  • 00:05:13
    as a particle accelerator so he used the
  • 00:05:15
    decay of radioactive elements to produce
  • 00:05:19
    his beams of particles this is
  • 00:05:22
    Rutherford's original desk and in fact
  • 00:05:25
    if you hunt around a little bit you can
  • 00:05:28
    detect
  • 00:05:30
    traces of
  • 00:05:32
    radioactivity 100 years
  • 00:05:37
    later Rutherford asked two of his
  • 00:05:39
    students Hans Gyer and Ernest Mazen to
  • 00:05:43
    fire some alpha particles at a piece of
  • 00:05:45
    thin gold foil and see what
  • 00:05:48
    happened so imagine these tennis balls
  • 00:05:51
    are the alpha particles now if the atom
  • 00:05:53
    were as Thompson had suggested a kind of
  • 00:05:55
    amorphous blob then you'd expect the
  • 00:05:58
    alpha particles to pass right
  • 00:06:00
    [Music]
  • 00:06:05
    through and that's indeed what happened
  • 00:06:08
    to most of them but to their surprise
  • 00:06:10
    they found that around one in
  • 00:06:15
    8,000 bounce right
  • 00:06:19
    back after two years of puzzling over
  • 00:06:22
    the meaning of these results Rutherford
  • 00:06:24
    realized that in order for the alpha
  • 00:06:26
    particles to bounce back they must hit
  • 00:06:28
    something small
  • 00:06:30
    and dense so his new model of the atom
  • 00:06:32
    was a bit like the solar system with all
  • 00:06:35
    the mass concentrated at the center and
  • 00:06:37
    the electrons orbiting like planets
  • 00:06:40
    around the Sun today we know that this
  • 00:06:43
    picture isn't quite correct quantum
  • 00:06:46
    mechanics tells us that we can't know
  • 00:06:48
    precisely where the electrons are but we
  • 00:06:51
    can predict that they reside in distinct
  • 00:06:53
    shells around the nucleus Rutherford's
  • 00:06:56
    alpha particle scattering experiment was
  • 00:06:59
    remarkably direct and simple and it
  • 00:07:01
    showed the nature of what the atomic
  • 00:07:03
    structure is by the way the alpha
  • 00:07:06
    particles bounc off the atom he worked
  • 00:07:08
    out where the positive charge of the
  • 00:07:09
    atom lives Rutherford had come to the
  • 00:07:11
    astonishing conclusion that most of the
  • 00:07:14
    atom and therefore most of what we think
  • 00:07:16
    of as ordinary matter is in fact empty
  • 00:07:19
    space so if this apple with the atomic
  • 00:07:22
    nucleus the electrons would be a
  • 00:07:25
    kilometer away after discovering the
  • 00:07:28
    nucleus brother had continued doing
  • 00:07:30
    experiments firing particles at
  • 00:07:32
    different targets to delve into the
  • 00:07:35
    structure of the nucleus Itself by 1932
  • 00:07:39
    Rutherford and his colleague James
  • 00:07:40
    Chadwick had found that the nucleus is
  • 00:07:42
    made of two kinds of particles
  • 00:07:45
    positively charged protons and
  • 00:07:47
    electrically neutral
  • 00:07:49
    neutrons the discovery in these
  • 00:07:52
    experiments of neutrons uncharged atoms
  • 00:07:55
    of mass one has proved of great
  • 00:07:58
    significance
  • 00:08:00
    and importance and has given us a much
  • 00:08:03
    clearer understanding of the actual
  • 00:08:05
    structure of
  • 00:08:08
    nuclei less than a century after Mela
  • 00:08:10
    published his periodic table scientists
  • 00:08:13
    had arrived at a seemingly beautiful
  • 00:08:16
    simplification all this is made of just
  • 00:08:19
    three fundamental particles the proton
  • 00:08:22
    the neutron and the electron this was a
  • 00:08:25
    giant step forward in our understanding
  • 00:08:27
    of matter but there were still phenomena
  • 00:08:29
    that couldn't be explained in terms of
  • 00:08:31
    just these three
  • 00:08:35
    particles in the early 20th century
  • 00:08:37
    scientists recorded mysterious new
  • 00:08:40
    particles bombarding the Earth from
  • 00:08:42
    outer space they had discovered cosmic
  • 00:08:44
    rays and they rushed to study them by
  • 00:08:48
    the late 1930s they came to the
  • 00:08:50
    conclusion that the experimental results
  • 00:08:53
    could not be explained using the then
  • 00:08:55
    known fundamental particles protons
  • 00:08:58
    neutrons and
  • 00:09:00
    electrons some other more mysterious
  • 00:09:03
    particles were
  • 00:09:05
    responsible using cosmic rays to detect
  • 00:09:07
    new particles isn't particularly
  • 00:09:09
    efficient however because you never know
  • 00:09:11
    when or where they're going to turn up
  • 00:09:13
    it'll make much more sense to make your
  • 00:09:15
    own thus entered into physics this the
  • 00:09:19
    particle accelerator a way of making
  • 00:09:22
    cosmic rays in the
  • 00:09:26
    laboratory particle accelerators built
  • 00:09:28
    in the 194 40s and 50s led to the
  • 00:09:31
    discovery of many new particles given
  • 00:09:33
    exotic names like P sigmas lambdas and
  • 00:09:39
    Deltas by the mid 1960s over 80
  • 00:09:43
    apparently fundamental particles have
  • 00:09:45
    been discovered so many in fact that
  • 00:09:47
    particle physicists began to refer to
  • 00:09:49
    them as a zoo this was no better than
  • 00:09:52
    melev's periodic table eventually order
  • 00:09:56
    and elegance were restored by American
  • 00:09:58
    physicists Mary galman there was a
  • 00:10:02
    comparatively simple underlying
  • 00:10:03
    structure to all this and the
  • 00:10:05
    classification say of the strongly
  • 00:10:07
    interacting particles depended a great
  • 00:10:10
    deal on symmetries and broken in
  • 00:10:13
    particular broken symmetries approximate
  • 00:10:16
    symmetries that were
  • 00:10:18
    violated galman had noticed patterns
  • 00:10:21
    which physicists can explain in terms of
  • 00:10:24
    symmetries and by identifying the
  • 00:10:26
    underlying symmetries he found he could
  • 00:10:29
    explain the properties of the
  • 00:10:32
    particles according to him protons
  • 00:10:35
    neutrons and the whole zoo of apparently
  • 00:10:38
    fundamental particles were made up of
  • 00:10:40
    just three types of basic building
  • 00:10:42
    blocks which he named quarks just a
  • 00:10:46
    simple inspection of the uh particle
  • 00:10:48
    chart would suggest immediately the cork
  • 00:10:51
    scheme so the difficult thing was not
  • 00:10:55
    noticing the cork scheme that was
  • 00:10:57
    essentially trivial what was difficult
  • 00:11:00
    was
  • 00:11:00
    believing that it had any
  • 00:11:07
    relevance for anything for anything for
  • 00:11:10
    anything at all to happen in the
  • 00:11:14
    universe for a force must
  • 00:11:27
    act there for anything at all to happen
  • 00:11:31
    in the
  • 00:11:31
    [Music]
  • 00:11:34
    universe a force must act
  • 00:11:41
    [Music]
  • 00:11:52
    [Music]
  • 00:12:00
    we usually think of forces as moving
  • 00:12:02
    things around pulling this apple towards
  • 00:12:05
    the ground or pushing a car up a hill
  • 00:12:08
    but forces also cause the sun to shine
  • 00:12:11
    they make the ice melt in your drink and
  • 00:12:14
    they cause a plant to emerge from a seed
  • 00:12:17
    forces are the Agents of change in the
  • 00:12:23
    universe to help us understand forces
  • 00:12:26
    thousands of scientists around the world
  • 00:12:28
    have spent billions of pounds to build
  • 00:12:31
    this machine I'm standing 100 met below
  • 00:12:34
    the ground at CERN in Geneva and this is
  • 00:12:38
    the CMS detector part of the largest and
  • 00:12:41
    most complicated scientific experiment
  • 00:12:44
    ever
  • 00:12:46
    attempted this experiment will give us
  • 00:12:48
    deeper insight into the forces of nature
  • 00:12:51
    than ever
  • 00:12:52
    before it's a long way from when Isaac
  • 00:12:54
    Newton pondered the laws of gravity but
  • 00:12:57
    all part of the same story okay
Tags
  • particles
  • atom
  • electron
  • Rutherford
  • quarks
  • forces
  • CERN
  • Thomson
  • Mendeleev
  • neutron