Physics
What Is Light Made of? A Brief History of the Wave-Particle Duality Idea
For thousands of years, the nature of light has remained a mystery for philosophers and scientists. Sure, you can tell that there’s something there, because when there’s no light source, like during the night, or in a dark room, you can’t see. But what is it exactly, what is made of, and does it work?
The first person to try to explain the nature of light in scientific terms was Isaac Newton, in his 1704 treatise called Opticks. For him, light was made out of particles he called corpuscles which behaved just tiny balls, obeying the famous laws of motion he himself put forth earlier. This theory, for example, could explain reflection (in terms of ball-like particles bouncing off a surface) and refraction (when passing from one medium to another, the particles are briefly attracted by the second medium, which gives them a slight kick in speed). Newton’s theory was accepted at the time because it made sense (and also because he was Newton), but the idea that light was actually a wave didn’t completely fade into obscurity.
This idea made a great comeback about a century after Newton’s treatise with the experiment of an English scientist named Thomas Young. Known as the double-slit experiment, it involved shining a light two narrow openings in a wall and observing the pattern it displays when hitting a screen. If light is made out of particles, we’d expect to see a couple of bright lines directly behind the two slits and nothing else. If light is a wave, however, like the ripples you see on the surface of a pond when you drop something in it, you’d expect the two like beams to interfere with each other. When Young did this experiment, he found the latter was true.
Illustration of the pattern observed when shining a laser through a single-slit and a double-slit. You can clearly see the interference pattern in the second example. Image: Wikimedia Commons
The image above illustrates what this looks like with a laser (Young himself, working 200 years ago, used sunlight). So why do we see a series of bright bands with dark bands between them? Well, these are caused by the beam of light splitting into two waves which then spread out and interfere with each other. We know that a wave has a peak and a trough. Where two peaks or two troughs meet, the amplitude of the wave is increased – we call that constructive interference. Where a peak and a trough meet, they cancel each other out (destructive interference). This is why we see a series of bright and dark spots on the screen behind the two slits. We can also see that, if there’s a single opening for the light to go through, there’s no longer any interference pattern.
So the debate seemed to have been settled: light was not made of particles, but was actually a wave. But a century after Young’s experiment, another great scientist would come along and, at least partially, vindicate Newton’s views on the nature of light – a scientist called Albert Einstein. One of the hugely influential papers he published in 1905 tackled precisely this subject. Attempting to explain a series of recent observations and experiments, Einstein postulated that light was actually made up of discrete units, or quanta. Particularly important is the fact that this idea explained the photoelectric effect, an observation that metals emits electrons when shining a light onto them. This explanation was so elegant and effective that, out of all his great achievements in physics, it was this one that was specifically mentioned when Einstein was awarded the Nobel Prize in 1921.
By this time, physicists were beginning to realize nature was a lot more complicated than previously thought. One of the consequences was that they no longer attempted to describe light simply as a particle or as a wave – but rather as both. This is what’s called the wave-particle duality of light. Other experiments would subsequently find that not only light behaves like this, but also electrons, individual atoms, and even huge molecules like carbon-60 buckyballs. So the age-old search for the nature of light has ultimately revealed something profound and astonishing about everything in nature: we are all made up of both particles and waves!
Physics
An interest They stepped on a rock and found something on Mars that had never been seen before
NASA’s curiosity has been looking into an interesting part of Mount Sharp for the past 10 months. It shows signs of a violent watery past, and chemical tests have shown that it contains many minerals, such as sulfates. The rover also broke open a rock by accident as it moved around. And inside it were crystals of pure sulfur.
On Mars, people had never seen pure sulfur before. Even though sulfates contain sulfur, there isn’t a clear link between how those molecules form and how the pure crystals form. Crystals of elemental sulfur can only form in a few different situations. And none of those were thought to happen in this area.
To find a field of stones made of pure sulfur is like finding an oasis in the middle of the desert, said Ashwin Vasavada, the project scientist for Curiosity at NASA’s Jet Propulsion Laboratory. “That thing shouldn’t be there, so we need to explain it.” It’s so exciting to find strange and unexpected things when exploring other planets.
The Gediz Vallis channel is the name of the area that Curiosity is exploring. A groove across Mount Sharp has been interesting for a long time, even before the rover started climbing it in 2014. From space, scientists could see that there were big piles of debris. But it wasn’t clear what caused them. Was it landslides or floodwaters from a long time ago that moved the stuff along the channel?
The answer has been found through curiosity. Some column A and some column B. Water-moved rocks are smoother and rounder. Sharp and angular are those that dry avalanches moved. There are both kinds of rocks in the mounds.
“This was not a quiet time on Mars,” said Becky Williams, a scientist from Tucson, Arizona, who works for the Planetary Science Institute and is the deputy principal investigator of Mastcam on Curiosity. “There was a lot of exciting stuff going on here.” We expect a number of different flows to happen down the channel, such as strong floods and flows with lots of rocks.
Curiosity is still looking into the Gediz Valley. When the ball rolls around and shows off its unique features, we can get very excited about the science being done here.
To figure out if there is life in other parts of the universe, we start with Earth, where there is life now. Finding another Earth is a good way to find aliens. We have found more than 5,000 exoplanets, but we haven’t found Earth’s twin yet. This could change soon, though. Here comes the PLATO mission from the European Space Agency (ESA).
What does PLATO stand for? It stands for PLAnetary Transits and Oscillations of stars. Its goal is very clear. It will look for nearby stars like the Sun that might have habitable worlds like Earth.
“One of the main goals is to find a way to compare Earth and the Sun.” The size of Earth is in the habitable zone of a star like the Sun. “We want to find it around a star that’s bright enough that we can really figure out how heavy it is and how big it is,” Dr. David Brown from the University of Warwick told IFLScience. “If you like, that’s our main goal.”
The telescope is not only an observatory for looking for planets, but it is also an observatory for collecting data on a huge number of stars. The mission team thinks that the fact that it can do both is a key part of why this telescope will be so important.
“You have two parts of the mission.” One is exoplanets, and the other is the stars. “From a scientific point of view, I think it’s pretty cool that these two parts are working together to make the best science we can,” Dr. Brown said.
One of the secondary goals is to make a list of all the planets that are Earth-like and all the star systems that are out there. One more goal is to find other solar systems that are like ours. Even though we don’t know for sure if our little part of the universe is truly unique, it does seem to be different from everything else.
Dr. Brown told IFLScience, “We have a bunch of other scientific goals.” “Really, how well do we know how planetary systems change and grow over time?” Planetary systems are something we’re trying to understand as a whole, not just one planet at a time.
PLATO is different in more ways than just the goals. It is not just one telescope. In fact, it’s made up of 26 different ones. Two of the cameras are fast, and the other 24 are normal cameras set up in groups of six with a small gap between them. This makes the telescope work better, has a wider field of view, and lets you quickly rule out false positives.
It can be hard to tell which of the things you find when you transit exoplanets are real and which ones are not. With the help of several telescopes, we were able to block out some of the mimics that we would have seen otherwise. “Plus, it looks pretty cool,” Dr. Brown said with excitement. “This big square with all of these telescopes pointing at you looks really cool!”
This week, Dr. Brown gave an update on PLATO at the National Astronomy Meeting at the University of Hull. The telescope is being put together and has recently passed important tests. There are no changes to the planned launch date for December 2026. An Ariane 6 rocket, the same kind that made its first launch last week, will take off from French Guiana.
Einstein’s theory of special relativity says that it is impossible to move faster than light in a vacuum.
Things that don’t have mass have to move at the speed of light. But things that do have mass can’t get close to 299,792,458 meters per second (983,571,056 feet per second) without using up all of their energy. Physicists and sci-fi authors have tried to get around this by using concepts like the warp drive. But it’s likely that these will be illegal because of those pesky physics laws. Traveling faster than light can cause paradoxes that break the rules of the universe.
You are not in a dark room, though, because there is something in this room right now that can slow down or stop light. It is possible for shadows to go faster than light, and they can even smash through it.
You might ask things like, “What the hell are you talking about?” Imagine that you have a flashlight that is strong enough to light up some of the moon. If you quickly move your finger across the front of the flashlight, the shadow it casts can move across the moon’s surface at speeds much faster than light.
If you wave a laser across the night sky, you can get the same kind of effect. Think of a huge dome that is, say, 100 light-years across and surrounds you. When this laser hits that dome 100 years from now, the points will fly across it at speeds much faster than light.
But these two examples are just tricks.
Astrophysicist Michio Kaku told Big Think, “There is no message, no net information, and no physical object that actually moves along this image. There is only the image of the beam as it races across the night sky.”
No, the laser point isn’t really moving. What you’re seeing are photons hitting the dome and then different photons hitting a different part of the dome 100 years later after you moved your laser.
The universe and physics stayed the same because nothing really moved faster than light, and no information was sent.
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