The Boltzmann brain is a thought experiment that questions whether our universe is real

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The Boltzmann brain is a thought experiment that questions whether our universe is real

the gist

The Boltzmann brain is a thought experiment in which a brain forms by random chance out of the disorder of the universe, complete with false memories of a past it never had. Ludwig Boltzmann proposed in 1896 that the universe could fluctuate into ordered states, and physicists realised that such random fluctuations would be far more likely to produce a single brain than an entire universe like ours. Because a lone brain is the simplest possible outcome, theories that predict mostly Boltzmann brains are considered to be wrong. Physicists use the idea to test their assumptions about thermodynamics and cosmology.

how it works

Random thermal fluctuations can in principle assemble any arrangement of particles, given enough time. A small arrangement like a brain is far more likely to appear by chance than a huge, orderly universe, so a theory that predicts mostly such brains would predict that we are probably illusions.

so what

The idea shows how cosmology can use a strange thought experiment to reject theories rather than just test them. It remains an unsolved problem tied to the measure problem in multiverse theories.

the bigger pattern

Boltzmann's own work on entropy was controversial in his lifetime, and his later ideas about fluctuations keep returning in modern cosmology, especially in debates about eternal inflation.

Hampi was once one of the world's largest cities, until its Vijayanagara capital was destroyed in 1565

the gist

Hampi is a UNESCO World Heritage Site in Karnataka, India, with more than 1,600 surviving remains spread over 4,100 hectares. It was the capital of the Vijayanagara Empire from 1336 to 1565. Travellers from Persia and Portugal described it as a prosperous, wealthy and grand city with temples, markets and farms along the Tungabhadra River. By 1500 it was estimated to be the world's second-largest city after Beijing, and probably India's richest at the time. In 1565 a coalition of Muslim sultanates defeated the Vijayanagara Empire, its capital was conquered and destroyed, and the city was left in ruins. Hampi remains a religious centre, with the active Virupaksha Temple at its heart.

how it works

The city was built around a fortified core with temples, markets and water structures along the river, supplied by an extensive network of roads and waterworks. When the empire fell, the city was not rebuilt, so its stone monuments were left standing.

so what

Hampi shows how quickly a great city can vanish after a military defeat, and how a ruined capital can remain sacred. Its ruins give historians a view of medieval South Asia that few other sites can match.

fun fact

The name Hampi comes from Pampa, an old name for the Tungabhadra River.

From Wikipedia, the free encyclopedia · text CC BY-SA 4.0

Image: Wikimedia Commons

source: Wikipedia ↗

2 min

politicsshortCNA2:01

False allegations about Singapore’s hand in Indonesia’s markets and a made-up meeting

from CNA

CNA Verify has found close to 400 posts pushing falsehoods tying Singapore to Indonesia’s stock market rout and to a secret meeting that never took place. Together, they drew nearly 12 million views, and some were circulated by accounts that appeared to be working in concert, across multiple social media platforms.

Here’s how the disinformation campaign targeting Singapore was uncovered.

on YouTube: CNA ↗