Minneapolis Protester Killed, Science of Light, and Famous Gold Hoards

What even is light?

Light is a type of energy that communicates information about the world. When this energy is emitted or reflected by objects, it can be collected—as occurs in the human retina—and processed to make observations, identify surroundings, and produce data. This has enabled humans to develop scientific models for a broad range of phenomena, which have been used to explain nature and create nearly every piece of technology in existence.

Historically, observations of light bouncing off mirror-like surfaces suggested it was composed of a stream of particles—later called photons—while its ability to bend and spread around obstacles indicated it was instead a wave. The development of theories in electromagnetism and quantum physics reframed light as exhibiting properties of both waves and particles, known as the wave-particle duality. The variety of optical characteristics in different types of light (e.g., color) results from variations in the properties of waves and photons, such as frequency and energy.

The continuum of all electromagnetic radiation is known as the electromagnetic spectrum, which consists of radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays. All electromagnetic radiation travels at 299,792,458 meters per second—one of the fundamental constants of the universe—in the absence of matter. However, differences in the properties of these bands make each useful for distinct applications, including telecommunications, food preparation, sterilization, medical imaging, and radiosurgery.

... Read what else we learned about light here.

Also, check out ... 

> Rayleigh scattering gives us blue skies and red sunsets. (Watch)

> Nearly all life on Earth depends on photosynthesis, a process powered by sunlight. (Explore)

> How solar panels transform light energy into electricity. (Watch)

> Photons do not experience distance or the passage of time. (Watch)

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What made the man so legendary?

Warren Buffett is the former CEO of the world’s largest holding company, Berkshire Hathaway, and is largely considered the most successful investor in history. His philosophy and decisions are widely followed by others in the industry, and Berkshire's shareholder letter is eagerly anticipated each year.

Born in 1930 in Omaha, Nebraska (where he still resides), Buffett bought his first stock at age 11 and made his first real estate investment at age 14.

In 1965, Buffett took over Berkshire Hathaway after purchasing enough of its dying stock. It was originally a textile company, but Buffett transformed it into the most successful holding company in the world, liquidating its textile assets and instead investing in insurance companies. From when he took over through the 1990s, Berkshire Hathaway's stock rose between 10% and 20% every year.

... Read our full explainer on Warren Buffett here.

Also, check out ... 

> Buffett plans to donate 99% of his wealth to philanthropy. (Read)

> Why Warren Buffett paid a lower effective tax rate than his secretary. (Watch)

> Though famously frugal, Buffett owns a private jet. (Read)

> Read Berkshire Hathaway's shareholder letters from 1977 on. (Explore)

How US federalism works

Federalism is a system of government in which power is divided between national and state governments, and it exists in roughly two dozen countries worldwide. It differs from unitary systems, in which provinces, states, or regions can have their powers changed, revoked, or overruled by a central authority.

Disagreements over federalism defined politics in the early American republic. Following the failure of the Articles of Confederation, which had created a national government too weak to function effectively, the Constitution established a federal system with a stronger central authority, while preserving the states as autonomous centers of power. It maintains this balance by specifying federal responsibilities, giving Congress the flexibility to act when necessary, and leaving most day-to-day governance to the states.

Throughout American history, federal power has expanded relative to the states, primarily through Supreme Court rulings and national responses to crises. Today, federalism debates play out in clashes among federal, state, and local governments over issues like abortion and immigration.

... Read our full write-up on US federalism here. (This page is part of our special Civics section, sent each Thursday in the Daily Digest to commemorate the 250th anniversary of the US. This week, we'll be exploring the executive branch—stay tuned!) 

Also, check out ... 

> How an adultery and poisoning case examined whether federal treaty power supersedes state law. (Listen)

> See which countries use a federal system—and how they work. (Explore)

> Alexander Hamilton and Thomas Jefferson's main disagreements were over federalism. (Watch)
> Federalism creates tension between national and state power by design. (Read)

In partnership with Fisher Investments

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Introducing: 1440 Health & Medicine

Best of the Week

We added 313 resources this week to our knowledge collective—here are the most informative and fascinating. 

Chinese EV-maker BYD overcame Tesla in total sales with help from China and by targeting cheaper cars. (Watch)

Peruse a trove of 22 gold coin hoards discovered over the millennia. (Read)

How two migrants built Kalshi, the first regulated prediction market in the US. (Read)

Why does the US have military bases in Greenland? A treaty signed in 1951. (Read)

Snowflakes are made when water vapor (rather than liquid water) freezes. (Watch) 
 

Davos, Switzerland—the site of the annual World Economic Forum—is also one of the highest cities in Europe. (Read)

A look at the roughly 1,400 oil tankers used in the global "dark fleet" to avoid sanctions. (Watch)

Georgia O'Keeffe's chow chows, Jackson Pollock's heelers: a gallery of famous artists with their dogs. (View)
 

The 9 billion voice notes sent every day are multiplying our monologues. (Read)

How the Indiana Hoosiers went from all-time losing record to a perfect championship season. (Read)

A look at common sources and main functions for each vitamin. (View)  

Netflix is looking to buy Warner Bros. as it increases its slate of low-cost reality TV programming. (Read)

The nations where major populations of certain religions are concentrated. (View)

Lessons learned from one New Yorker's experience during "No-Buy January." (Read)

Most Americans support age limits on Congress, Supreme Court. (Read)

Historybook: First Winter Olympics take place in Chamonix, France (1924); Battle of the Bulge comes to an end (1945); Al Capone dies (1947); Alicia Keys born (1981); Mary Tyler Moore dies (2017).