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  • [♪ INTRO]

  • The whole point of physics has always been to understand what

  • the universe is made of and how the stuff in it interacts.

  • You know, like how Isaac Newton wanted to figure out why

  • an apple always falls straight toward the ground.

  • And we've come a really long way over the years.

  • These days, after about a century of incredible research in

  • fundamental physics, we have a pretty good idea of

  • the building blocks that make up everythingand the rules

  • that describe how they interact.

  • In fact, our fundamental picture of the universe seems

  • so nearly complete that it's led some people to suggest

  • that we're arriving at some version ofthe end of physics.”

  • And for sure, physics is at a turning point,

  • but before researchers pack it up and head home,

  • it's worth understanding what the so-calledend of physics

  • is really all about.

  • As far as anyone can tell, every single thing in our entire world

  • is made up of a small handful of elementary particles,

  • like electrons and quarks.

  • And they obey very strict rules when they interact with each other.

  • Starting with those basic particles and the rules they follow,

  • you can build up to all sorts of thingslike the physics of baseball,

  • the chemistry of pie-baking, or the biology of cell division.

  • Of course, it doesn't make much sense to explain

  • how something like the brain works using elementary particles like quarks.

  • It usually makes more sense to describe reality

  • with bigger things, like molecules or cells.

  • But the point is, no matter what unit makes the most sense to use,

  • that unit still obeys the same basic principles.

  • Like, you're not going to need a brand-new

  • elementary particle to make sense of some everyday thing,

  • like how a bird flies.

  • Most of the basic rules that describe the stuff

  • in our everyday world are part of a framework called

  • the Standard Model.

  • This framework is essentially a set of math and physics principles

  • that describe the fundamental structure of the world as we know it.

  • It includes three of the world's four fundamental forces

  • and the couple dozen particles related to them.

  • Those three forces are the electromagnetic force, the strong force,

  • and the weak force, and they fit neatly into the Standard Model.

  • But there is one more fundamental force: gravity.

  • And it's a little bit of an oddball because it's not neatly described

  • by the physics of elementary particles, like the other forces are.

  • So it doesn't fit into the Standard Model.

  • And that's part of the reason there's no theory of everything

  • that neatly ties up all the forces and particles in the universe.

  • But, even without a theory of everything, the Standard Model

  • and general relativity do a solid job of describing almost

  • everything in our world.

  • Which is a pretty tall order, all things considered.

  • These theories are the culmination of a century's worth

  • of research into fundamental physics.

  • And it can be tempting to see fundamental physics

  • as a puzzle with almost all the pieces in place.

  • Which kind of sounds like the end of the road for physicists.

  • But before anyone calls it a day or, like,

  • converts to a biologist, there are a few things to consider.

  • First of all, there were plenty of times throughout history

  • when scientists thought physics was basically complete

  • and each time, they were extremely wrong.

  • For instance, in the 1920s, even after we discovered the mysteries

  • of quantum mechanics and relativity, the physicist

  • Max Born still had the nerve to say that

  • physics, as we know it, will be over in six months.”

  • Spolier! It wasn't.

  • Then, there was that time at the end of the 19th century

  • when the physicist Albert Michelson said,

  • It seems probable that most of the grand underlying principles

  • have been firmly established.”

  • This guy was ready to call it quits before we even knew about

  • quantum stuff and relativity!

  • Physicists at the time had been so used to the laws of motion

  • discovered by Isaac Newton that they expected them to work forever,

  • for everything.

  • The thing was, by the time he'd said that, Michelson himself

  • had already conducted an experiment that would go on to prove him

  • and the whole Newtonian worldviewwrong.

  • The Michelson-Morley experiment, as it's called,

  • provided strong evidence that there isn't any universal,

  • absolute reference frame that everything can be measured relative to,

  • as Newton's way of thinking suggested.

  • That experiment was crucial in paving the way for relativity.

  • And the move from an absolute to a relativistic way of thinking

  • about motion totally upended what we'd thought for centuries

  • about how the universe works.

  • As a result, Einstein had to come in and invent

  • a whole new way to describe space and time.

  • So, back in Michelson's day, thegrand underlying principles

  • of physics still had a long way to go.

  • Basically, every time someone like Born or Michelson thought

  • they had all the answers, they realized that their framework

  • was just a really good approximation of reality.

  • Once you got out to certain extremes, that approximation

  • started to break down.

  • In other words, their frameworks did a good job of describing

  • the world under certain conditions, but they weren't

  • perfect explanations.

  • And the same thing is likely true of the Standard Model

  • and general relativity.

  • They seem fundamental because they describe the universe really well,

  • but in extreme environments like black holes or the Big Bang,

  • those frameworks still seem to break down.

  • And there are still some problems with the laws we call fundamental.

  • I mean, just the fact that gravity doesn't mirror the other three

  • fundamental forces suggests that some piece of the story

  • is still missing.

  • And there are other imperfections that constantly remind us

  • that our fundamental theories are just a really good

  • approximations of reality.

  • Meaning it's almost certainly not the end of the road.

  • Instead, we're in a kind of weird, unprecedented era

  • where physicists know our theories aren't complete, but they also

  • have very little evidence for anything beyond it.

  • That makes it much harder to make progress now than it was

  • a hundred years ago.

  • Because the thing is, Michelson and Morley were able to disprove

  • the fundamental laws of their time using a lab experiment

  • that can now be done in a college classroom.

  • But the times have changed.

  • People have plucked all the low-hanging fruit.

  • If you want to make discoveries about fundamental physics these days,

  • you need really big experiments.

  • In 2012, the Large Hadron Collider at CERN in Switzerland

  • discovered the last particle missing from the Standard Model,

  • the Higgs boson.

  • That was a gargantuan international collaboration involving

  • billions of dollars, thousands of scientists and engineers,

  • and an army of support staff.

  • You're simply not going to find an undiscovered particle

  • without that kind of tech, because you need something

  • that can create conditions way more extreme than you get

  • in everyday life.

  • And as much as theoretical physicists hoped that

  • the Large Hadron Collider would find evidence of physics beyond

  • the Standard Model, it simply hasn't.

  • But the fact that it's difficult doesn't mean

  • that there is nothing left to find.

  • And the good news is, modern physicists understand this better

  • than people like Michelson did back in the day.

  • So they're not claiming that the job is done.

  • They know that there are stillgrand underlying principles

  • that haven't been discovered, and tons of ways

  • that our current theories are incomplete.

  • Just like what happened with relativity back in the day,

  • the solution to the problem will likely be a whole new theory

  • that only looks like the Standard Model or general relativity

  • under the right conditions.

  • Fundamental physics has reached a very high plateau

  • with our current theories.

  • But without enough experimental evidence to guide it higher,

  • it's also kinda stuck in a rut.

  • The good news is, there are still lots of ways

  • theoretical physicists are pushing forward.

  • For one, finding ways to unify the fundamental laws of physics

  • is still a huge area of research.

  • In some cases, physicists know where the fundamental laws

  • break downlike in black holes.

  • There, both relativistic effects and quantum mechanical effects

  • are relevant, but they don't agree on what should happen.

  • General relativity says black holes should evaporate into nothing,

  • but quantum mechanics says that's not possible.

  • So we simply don't know what's right.

  • But scientists have begun figuring out ways to research

  • those kinds of environments.

  • Like, to get around the fact that they can't exactly study things

  • like black holes in labs, they sometimes use what are called

  • analogous physical systems.

  • So rather than study, say, a black hole directly,

  • physicists study a system that has similar properties.

  • For instance, one of the most important properties of black holes

  • is that they don't let light escape.

  • So physicists found a way to make a similar system in a lab

  • except instead of trapping light, their system traps sound.

  • This is called an acoustic black hole.

  • And these things actually reproduce properties we'd expect to see

  • in real black holes.

  • Scientists are hoping that they can help figure out the real fate

  • of black holes, since relativity and quantum mechanics disagree.

  • Another team of researchers found a way to put ultracold helium atoms

  • in a state where they behave like Higgs boson particles,

  • and they were able to use that to study properties of the Higgs

  • even before they had discovered the Higgs boson itself.

  • In general, you can use the concept of analogous systems

  • to invent all sorts of unusual environments that'll

  • make particles behave in ways they normally wouldn't,

  • and that's been one way for physicists to push the limits

  • of fundamental physics.

  • But these days, it's not the only way to study

  • the fundamentals of reality.

  • As computers get more and more powerful, simulations of

  • physical systems have become much more common

  • in fundamental physics research.

  • And simulations have been a total game-changer, because in the past,

  • just knowing the basic rules that govern a system

  • wasn't enough to tell how the system would behave in practice.

  • For instance, it would take way too much number-crunching

  • for a human to figure out how the laws of physics would play out

  • over billions of years of galactic evolution.

  • But with simulations, computers do the work of figuring out

  • how the laws of physics play out under certain conditions

  • in a fraction of the time.

  • Based on the results, scientists make predictions about

  • how those systems behave in the real world.

  • And that can get us a long way!

  • Like, predicting the chaotic movement of weather systems

  • would be close to impossible without advanced computer simulations,

  • no matter how well you understand how particles work.

  • And simulations are currently the only way to test theories

  • about things like the evolution of the early universe.

  • So even without new particles or forces, fundamental physics

  • is still pushing forward.

  • Clearly, theoretical physics isn't done.

  • But it has changed, for sure.

  • The next plateau in our search for the theory of everything

  • isn't going to be reached by a lone maverick working alone in a lab.

  • It's going to take contributions from thousands of researchers

  • across the globe, doing everything from writing equations

  • to examining astronomical data to programming computers.

  • The plateau we've reached with our latest theories is exciting,

  • but in some ways the things a theory can't explain

  • are more exciting than the things that it can.

  • Thanks for watching this episode of SciShow!

  • If you're interested in learning more about fundamental physics,

  • you can check out our four-part series that covers each one

  • of the fundamental forces.

  • It begins with the strong force, and you can get started

  • with that video right after this.

  • [♪ OUTRO]

[♪ INTRO]

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為什麼人們說我們已經到了物理學的盡頭? (Why Do People Say We've Reached the End of Physics?)

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    林宜悉 發佈於 2021 年 01 月 14 日
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