Is light a particle or a wave? – Colm Kelleher

Is light a particle or a wave? – Colm Kelleher


Translator: Andrea McDonough
Reviewer: Bedirhan Cinar You look down and see a yellow pencil lying on your desk. Your eyes, and then your brain, are collecting all sorts of information about the pencil: its size, color, shape, distance, and more. But, how exactly does this happen? The ancient Greeks were the first to think more or less scientifically about what light is and how vision works. Some Greek philosophers, including Plato and Pythagoras, thought that light originated in our eyes and that vision happened when little, invisible probes were sent to gather information about far-away objects. It took over a thousand years before the Arab scientist, Alhazen, figured out that the old, Greek theory of light couldn’t be right. In Alhazen’s picture, your eyes don’t send out invisible, intelligence-gathering probes, they simply collect the light that falls into them. Alhazen’s theory accounts for a fact that the Greek’s couldn’t easily explain: why it gets dark sometimes. The idea is that very few objects actually emit their own light. The special, light-emitting objects, like the sun or a lightbulb, are known as sources of light. Most of the things we see, like that pencil on your desk, are simply reflecting light from a source rather than producing their own. So, when you look at your pencil, the light that hits your eye actually originated at the sun and has traveled millions of miles across empty space before bouncing off the pencil and into your eye, which is pretty cool when you think about it. But, what exactly is the stuff that is emitted from the sun and how do we see it? Is it a particle, like atoms, or is it a wave, like ripples on the surface of a pond? Scientists in the modern era would spend a couple of hundred years figuring out the answer to this question. Isaac Newton was one of the earliest. Newton believed that light is made up of tiny, atom-like particles, which he called corpuscles. Using this assumption, he was able to explain some properties of light. For example, refraction, which is how a beam of light appears to bend as it passes from air into water. But, in science, even geniuses sometimes get things wrong. In the 19th century, long after Newton died, scientists did a series of experiments that clearly showed that light can’t be made up of tiny, atom-like particles. For one thing, two beams of light that cross paths don’t interact with each other at all. If light were made of tiny, solid balls, then you would expect that some of the particles from Beam A would crash into some of the particles from Beam B. If that happened, the two particles involved in the collision would bounce off in random directions. But, that doesn’t happen. The beams of light pass right through each other as you can check for yourself with two laser pointers and some chalk dust. For another thing, light makes interference patterns. Interference patterns are the complicated undulations that happen when two wave patterns occupy the same space. They can be seen when two objects disturb the surface of a still pond, and also when two point-like sources of light are placed near each other. Only waves make interference patterns, particles don’t. And, as a bonus, understanding that light acts like a wave leads naturally to an explanation of what color is and why that pencil looks yellow. So, it’s settled then, light is a wave, right? Not so fast! In the 20th century, scientists did experiments that appear to show light acting like a particle. For instance, when you shine light on a metal, the light transfers its energy to the atoms in the metal in discrete packets called quanta. But, we can’t just forget about properties like interference, either. So these quanta of light aren’t at all like the tiny, hard spheres Newton imagined. This result, that light sometimes behaves like a particle and sometimes behaves like a wave, led to a revolutionary new physics theory called quantum mechanics. So, after all that, let’s go back to the question, “What is light?” Well, light isn’t really like anything we’re used to dealing with in our everyday lives. Sometimes it behaves like a particle and other times it behaves like a wave, but it isn’t exactly like either.

33 thoughts on “Is light a particle or a wave? – Colm Kelleher

  1. If wave form is a sleeping form of energy.
    And whenever we looked at the photon represented awareness and hence acts as particle. Our thoughts and perception gives it shape. Just like what we think we become. What we feel we attract.

    And in the case, every time there was awareness/consciousness present.
    Light became particle. The medium of energy transfer.

    Just a thought

  2. You haven't answered your question.
    You said light behaves like a particle or a wave. Then what is it?.
    When you say a photon, a packets of what creature? Dark matter?.
    I believe light is a particle. For there to a wave there needs to be something. Like a photon. That's slips in the blackhole so that light will never collide.

  3. why isnt it just the particle being the one making the wave, as in the particle moving in a wave, or a wave with mass???

  4. Wave's and photon's do not exist it's impossible. Wave's of what? Look up Theoria Apophasis on YouTube, he also cover's extensively on Magnetism. The explanation's coming out of that guy's mouth with make your head fall off your shoulder's and flop on the floor

  5. If light was a particle, there would be no transparent objects like glass known to man because no one would think glass is transparent because particle of light wouldn't pass through any transparent object. Light is not a particle, its a wave in aether caused by excitation of aether. There is no photon particle either, what everyone think of as photon particle is simple a compression wave. Light bulbs do not emit anything, all it does is excites the aether with electricity and you have light. Entire physical universe is submerged in aether.

  6. What is weird enough (and I am not sure about the other countries), but in Russia this dualistic light behaviour is called "the corpuscular-wave theory of light" suggesting that Newton WAS kinda right.

  7. ppap + science

    i have a eletron
    i have a proton

    ohh particle(atom)

    i have energy
    i have light

    ohh waves

    particle
    waves

    ohh this is a my photon wave

  8. Sometimes it behaves like a particle and other times it behaves like a wave .
    But it isn't exactly like either !
    Video starts and ends on the same entangled question πŸ‘

  9. It's just like water. Sometimes you get drops of water ( particles) and when you put them together , you get waves . Just my way of making sense of it.

  10. Judt browsed by to do some fact checking. Great work, it looks like McCanney model of the solar system. How the sun acts as a capacitor sending out proton winds, attracting electrons and such. Jmccsci.com #mcanneysystems

  11. (Answer needed from TED ED itself)
    How light can act as a wave? (Because wave always requires a medium to move, just like a sound wave. And light also travels through vacuum). Does light contain any amount of physical matter? If light can sometimes be a wave, then can we believe in dark matter, present in vacuum to support the wave of light? How is light seen on microscopic level in a vacuum in contrast to a microscopic image of vacuum with no light? Or do I need to study something to get my answers?

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