-
7 votes
-
When leaders are bullies
5 votes -
CERN reveals plans for the Future Circular Collider (FCC) - almost four times longer than the current LHC
19 votes -
Fundamentals of Data Visualisation
3 votes -
Sleepers track informative speech in a multitalker environment
A report published in Nature Human Behaviour (hard paywall): Sleepers track informative speech in a multitalker environment An article published in the Sydney Morning Herald (soft paywall): Your...
A report published in Nature Human Behaviour (hard paywall): Sleepers track informative speech in a multitalker environment
An article published in the Sydney Morning Herald (soft paywall): Your brain is listening and processing while you sleep
A press release published in Mirage News (no paywall): Active sleep is more than just counting sheep
6 votes -
Fact: Calling out political furphies works, in Australia at least
An article from the Sydney Morning Herald: Fact: Calling out political furphies works, in Australia at least (with some local flavour) An article from New Scientist: Australians care if...
An article from the Sydney Morning Herald: Fact: Calling out political furphies works, in Australia at least (with some local flavour)
An article from New Scientist: Australians care if politicians tell lies, but people in the US don’t (from a non-Australian point of view)
The study itself in Royal Society Open Science: Does truth matter to voters? The effects of correcting political misinformation in an Australian sample.
4 votes -
The world's oldest person: Guinness, 122-year-old Jeanne Calment and a Russian conspiracy theory
9 votes -
All models are wrong
6 votes -
Some plants “hear” through flowers. A study found petals vibrated in response to recordings of a bee’s wingbeats, leading plants to sweeten their nectar.
10 votes -
It's the end of the gene as we know it
15 votes -
The world’s oldest woman was 122 when she died. A researcher believes that her daughter assumed her identity in the 1930s to avoid inheritance taxes.
28 votes -
Brain scans show social exclusion creates jihadists, say researchers
7 votes -
'Sonic attack' or just crickets? New analysis shows recording of 'attack' on US embassy was Caribbean wildlife
7 votes -
Computational chemists welcome ‘living’ journal
5 votes -
How one couple's adventure has uncovered secrets of humpback whales' survival
3 votes -
The science stories likely to make headlines in 2019
11 votes -
Thirty-five years ago, Isaac Asimov was asked by the Star to predict the world of 2019. Here is what he wrote.
29 votes -
Amoeba finds approximate solutions to NP-hard problem in linear time
11 votes -
The voice inside your head: The origin of “you”
8 votes -
Amoeba finds approximate solutions to NP-hard problem in linear time
7 votes -
AIDS – An approach for targeting HIV reservoirs
5 votes -
Researchers Show Parachutes Don't Work, But There's A Catch
14 votes -
The mad scramble to claim the world's most coveted meteorite
9 votes -
Randomness is random
8 votes -
After bloodbath, the National Zoo’s naked mole-rats finally choose their queen
10 votes -
Quantum physics in a mirror universe
4 votes -
How do you feel what you can't touch? Scientists crack the nerve code.
6 votes -
Scientists identify vast underground ecosystem containing billions of micro-organisms
9 votes -
Chinese scientist who used CRISPR on human babies gone missing
15 votes -
Scientists at the University of Oxford unifying dark matter and dark energy into a single phenomenon: a fluid which possesses 'negative mass"
27 votes -
Weewarrasauras: Lightning Ridge discovery the first dinosaur to be named in NSW in almost a century
2 votes -
Why smart people are vulnerable to putting tribe before truth
11 votes -
Successful second round of experiments with Wendelstein 7-X
22 votes -
First gene-edited babies claimed in China
12 votes -
A break in the quest for the quantum speed limit
4 votes -
How a change in climate wiped out the ‘Siberian unicorn’
3 votes -
A sci-fi writer and an anonymous 4chan poster advance a mathematical permutation problem
18 votes -
A layperson's introduction to Thermodynamics, part 3: Entropy and the heat death of the universe
Intro Hello everyone, Today we cover entropy and the heat death of the universe. The previous chapters can be found here and here. While I recommend you read both, you should at least read the...
Intro
Hello everyone,
Today we cover entropy and the heat death of the universe.
The previous chapters can be found here and here. While I recommend you read both, you should at least read the first part and skim the second.
A collection of all topics covered can be found here: https://tildes.net/~tildes/8al/.
Subject
Intro
Entropy describes how chaotic a system is. In thermodynamics, chaos is created from an irreversible process. We are all sort of familiar with this concept. A broken cup will not unshatter itself. As a consequence of how our universe works, (net) chaos can only increase. And this might have far reaching consequence, if we look at the effects of entropy on a cosmic scale.
Entropy
Entropy describes an amount of irreversible chaos.
But first, let's cover cycles super quickly. In thermodynamics, a very important concept is a "cycle". A cycle is a repeating process, that returns to its initial condition. For instance, when we ride a bike. We're turning our feet around the crank shaft. Repeatedly returning to the same position we started from. As we push on the pedal, some of our work is lost and turned into heat. Primarily due to friction from the wheels and from the different mechanical parts.
A cycle that wastes no energy is called a reversible cycle. That would mean 100% of the work in a cycle (even the work that is turned to heat) has to be returned in some way to its original state. The most famous example of this is the Carnot heat engine.[1] But in reality, the Carnot heat engine is nothing more than a theoretical engine. As we remember from before, we cannot turn 100% of heat back into work. So any heat engine, be it a car's motor, a refrigerator, a star, or the human body, will in some way contribute to this irreversible chaos.
Now what about entropy? If we look at entropy at the molecular level, it all becomes a bit abstract. But we can think of this concept with bigger building blocks than molecules, and still be close enough. Say you have a brick house with orderly layed bricks. This house would love to come crashing down. And lets imagine it does. When the house lays in ruins, it is not likely to suddenly "fall" into the shape of the house again. So if the house has collapsed, our system is in a higher state of chaos. Our entropy has increased. And unless we supply work to the system (and waste energy trough heat), we will not get the brick house back.
So now we understand, that on the grand scale of the universe, entropy will only increase.
The heat death of the universe
But what are the consequences of this? Imagine entropy going on for billions and billions of years. Everything in the universe slowly reaching a higher state of chaos. Everything that is orderly, turns into chaos. All high quality energy has turned into low quality energy. Everything has been wasted and turned into heat. Everything ripped apart until you are left with nothing to rip apart. At this point, there is no interactions between molecules any more. Everything has reached absolute zero temperature.
At this point, entropy is at its absolute maximum. And we have reached entropic equilibrium.
This is the heat death of the universe.
Afterword
Of course, the heat death of the universe is just one of the many theories about the end of the universe. It assumes that thermodynamics properly describes the universe, and that there are no hidden surprises.
Frankly told, it's the best bet we have with our current knowledge. But we still know so little. So I would not panic just yet. Alternatively, this is where we could continue with "an engineer's perspective on existensial nihilism". But I think that this is something better reserved for later, and better presented by someone else.
We have covered what I consider the absolute minimum of thermodynamics, that still gives us a basic understanding of thermodynamics. There are of course a lot of other topics we could cover, but thats it for now. I will potentially write an appendix later with some questions or things that have been asked.
But for now, that's it. Questions, feedback or otherwise?
Notes
[1] The Carnot heat cycle is a bit beyond the level of what we have discussed so far. It describes a system where heat is supplied and removed to have a piston expand and contract without any energy becoming waste heat.
14 votes -
A layperson's introduction to the nature of light and matter, part 1
Introduction I want to give an introduction on several physics topics at a level understandable to laypeople (high school level physics background). Making physics accessible to laypeople is a...
Introduction
I want to give an introduction on several physics topics at a level understandable to laypeople (high school level physics background). Making physics accessible to laypeople is a much discussed topic at universities. It can be very hard to translate the professional terms into a language understandable by people outside the field. So I will take this opportunity to challenge myself to (hopefully) create an understandable introduction to interesting topics in modern physics. To this end, I will take liberties in explaining things, and not always go for full scientific accuracy, while hopefully still getting the core concepts across. If a more in-depth explanation is wanted, please ask in the comments and I will do my best to answer.
Previous topics
Bookmarkable meta post with links to all previous topics
Today's topic
Today's topic is the dual nature of light and matter, the wave-particle duality. It is a central concept in quantum mechanics that - as is tradition - violates common sense. I will first discuss the duality for light and then, in the next post, for matter.
The dual nature of light
In what terms can we think of light so that its behaviour becomes understandable to us? As waves? Or as particles? There are arguments to be made for both. Let's look at what phenomena we can explain if we treat light as a wave.
The wave nature of light
Let's start with an analogy. Drop two stones in a pond, imagine what happens to the ripples in the pond when they meet each other. They will interact, when two troughs meet they amplify each other, forming a deeper trough. When two crests meet they do the same. When a crest and a trough meet they cancel out.
Now if we shine light through two small openings and observe the resulting pattern, we see it's just like ripples in a pond, forming an interference pattern. When looking at the pattern formed on a screen placed at some distance from the openings, we see a striped pattern Light can be described as an electromagnetic wave, with crests and troughs. It sure seems like light is wavey! The wave nature of light allows us to describe phenomena like refraction and diffraction.
The particle nature of light
When we shine light on some metals, they will start tossing out electrons. This is called the photoelectric effect. How can we understand this process? Well we know light is a wave, so we imagine that the wave crashes into the electron that is chilling out near the surface of the metal. Once the electron has absorbed enough of the light's energy it will be able to overcome the attractive forces between itself and the positively charged atom core (remember, an electron has negative charge and so is attracted to the atom cores). So a higher intensity of light should make the electron absorb the required amount of energy more quickly. Easy, done!
However, there's something very peculiar going on with the photoelectric effect. If we shine low frequency light on said metal, no matter how intense the light, not a single electron will emerge. Meanwhile if we shine very little high frequency light on the metal, no matter how low the intensity, the electron will emerge. But how can this be? A higher intensity of light should mean the electron is receiving more energy. Why does frequency enter into this?
It seems that the electron needs a single solid punch in order to escape the metal. In other words, it seems it needs to be hit by something like a microscopic billiard ball that will punch it out of the metal in one go. The way physicists understand this is by saying light is made up out of particles called photons, and that the energy a photon carries is linked to its frequency. So, now we can understand the photoelectric effect! When the frequency is high enough, the photons in the light beam all individually carry enough energy to convince an electron to leave the metal. When the frequency is too low, none of the photons individually can knock an electron out of the metal. So even if we fire a single photon, with high enough frequency, at the metal we will see one electron emerging. If we shine low frequency light with a super high intensity at the metal, not a single photon will emerge.
So there you have it! Light is made out of particles. Wait, what? You just told us it's made out of electromagnetic waves!
The wave-particle duality of light
So, maybe light is just particles and the wave are some sort of emerging behaviour? This was a popular idea, one that Einstein held for some time. Remember the experiment where we shone light through two small openings and saw interference (commonly known as the double slit experiment)? Let's just take a single photon and shoot it at the openings! Because light is particles we'll see the photon just goes through either opening - like a particle would. Then all the non-believers will have to admit light is made out of particles! However, when we do the experiment we see the photon interfere with itself, like it was a wave. Remember this picture which we said was due to wave interference of light? When a single photon goes through the openings, it will land somewhere on the screen, but it can only ever land in an area where the light waves wouldn't cancel out. If we shoot a bunch of photons through the openings one at a time, we will see that the photons create the same pattern as the one we said is due to wave interference!
Implications
So it would seem light acts like a particle in some cases, but it acts like a wave in some others. Let's take a step back and question these results. Why are we trying to fit light into either description? Just because it's convenient for us to think about things like waves and particles - we understand them intuitively. But really, there is no reason nature needs to behave in ways we find easy to understand. Why can't a photon be a bit wavey and a bit particley at the same time? Is it really that weird, or is it just our intuition being confused by this world we have no intuitive experience with? I would love to hear your opinions in the comments!
Observing photons
To add one final helping of crazy to this story; if we measure the photon's location right after it emerges from the slit we find that it doesn't interfere with itself and that it just went through a single slit. This links back to my previous post where I described superpositions in quantum mechanics. By observing the photon at the slits, we collapsed its superposition and it will behave as if it's really located at one spot, instead of being somehow spread out like a wave and interacting with itself. The self interaction is a result of its wavefunction interacting with itself, a concept that I will explain in the next post.
Conclusion
We learned that light cannot be described fully by treating it simply as a wave or simply as a bunch of particles. It seems to be a bit of both - but neither - at the same time. This forces us to abandon our intuition and accept that the quantum world is just fundamentally different from our every day life.
Next time
Next time we will talk about the dual nature of matter and try to unify the wave and particle descriptions through a concept known as the wavefunction.
Feedback
As usual, please let me know where I missed the mark. Also let me know if things are not clear to you, I will try to explain further in the comments!
Addendum
The photoelectric effect is actually what gave Einstein his Nobel prize! Although he is famous for his work on relativity theory he was very influential in the development of quantum mechanics too.
21 votes -
A break in the quest for the quantum speed limit
7 votes -
The “geno-economists” say DNA can predict our chances of success. Critics counter that their methods are naïve, offensive or both.
5 votes -
In solidarity with Library Genesis and Sci-Hub
28 votes -
At Yale, we conducted an experiment to turn conservatives into liberals. The results say a lot about our political divisions.
34 votes -
Astronomers have found a star that may produce the next gamma-ray burst in the Milky Way
10 votes -
The million-dollar drug: How a Canadian medical breakthrough that was thirty years in the making became the world’s most expensive drug — and then quickly disappeared
19 votes -
Cat tongue spines help smear saliva and inspire new 3D-printed brush
4 votes -
Kilogram gets a new definition
39 votes -
Is science stagnant? Despite vast increases in the time and money spent on research, scientific progress is barely keeping pace with the past
12 votes -
Why 536 was ‘the worst year to be alive’
14 votes -
When tulips kill: Antifungal resistance is here, and it could be just as dangerous to humans as antibiotic resistance
10 votes