Image for post
Image for post
The LHCb collaboration is far less famous than CMS or ATLAS, but the particles and antiparticles they produce, containing charm and bottom quarks, holds new physics hints that the other detectors cannot probe. (CERN / LHCB COLLABORATION)

The Universe, according to our best understanding, just doesn’t add up.

The Universe, according to our best understanding, just doesn’t add up. Wherever we look — from tiny subatomic scales all the way up to planetary, galactic, or even cosmic ones — we find that everything is overwhelmingly made of matter, rather than antimatter. We have a remarkable story of how our Universe came to be the way it is today: the hot Big Bang, as well as an understanding of how the particles that exist in our Universe behave: according to the rules of the Standard Model. But they can’t explain the Universe we know we actually inhabit.

The laws of physics, as we know them, aren’t perfectly symmetric between matter and antimatter, instead displaying subtle but important differences. These differences…


Image for post
Image for post
This 2016 long-exposure photograph shows Orionid meteors streaking across the sky in the east of Russia. The bright cone of light is not the parent comet of the meteor shower, Halley’s comet, but rather from a flashlight operated by a human on the ground. (Yuri Smityuk\TASS via Getty Images)

Halley’s comet only visits every ~76 years, but its meteors arrive twice each year.

The most famous comet of all — Halley’s comet — returns to our inner Solar System every ~76 years.

Image for post
Image for post
Halley’s comet made its most recent approach into the inner Solar System in 1986. In this long-exposure telescopic photograph, both the comet’s white dust tail and its blue ion tail are visible. However, the particles that make up a meteor shower are not visible here, but rather originate from the broken-up fragments of the comet’s nucleus. (F. Carter Smith/Sygma via Getty Images)

Using Newton’s gravitational law, Edmond Halley calculated that this 1682 comet also appeared in 1607 and 1531.

Image for post
Image for post
The orbit of Halley’s comet is largely determined by the Sun and makes a nearly perfect ellipse, but the periodicity of Halley’s comet has varied from 74 to 79 years as various close encounters with the outer planets have perturbed its orbit over the centuries. Its 76 year period is only a long-term average. (NAGUALDESIGN / WIKIMEDIA COMMONS)

In 1705, he predicted the comet’s 1758 return and every subsequent ~76 years thereafter, periodically.

Image for post
Image for post
This view of Halley’s Comet was photographed from space by the Soviet Probe “Vega” in 1986. The color gradient showcases the progressively decreasing density as particles are expelled from the comet’s nucleus. (USSR/Liaison via Getty Images)

This prediction was confirmed by Johann Georg Pallich, who observed Halley’s comet on Christmas Day, 1758.

Image for post
Image for post
Every ~76 years, Halley’s comet returns to the skies of Earth. Halley successfully identified the comet’s 1682 appearance with two prior periodic appearances, enabling a prediction of its return in 1758. Although Halley died in 1742, his predictions were not only borne out in that year, but periodically thereafter, including in a spectacular display in 1910. (Rodolfo Paoletti, L’Illustrazione Italiana, Year XXXVII, No 21, May 22, 1910; DE AGOSTINI VIA GETTY IMAGES)

Every 74–79 years, the comet returns: most recently in 1986 and next in 2061.

Image for post
Image for post
This view of Comet Halley’s nucleus was obtained by the Halley Multicolour Camera (HMC) on board the Giotto spacecraft, as it passed within 600 km of the comet nucleus on 13 March 1986. The comet was clearly quite active at the time. (ESA/MPAE LINDAU)

Like all comets, fragments break off when it approaches the Sun.

Image for post
Image for post
The debris stream of a comet — shown as the thin line in between the fragments — traces its orbit and give rise to meteor showers. Although the entire stream may be millions of kilometers wide, the peak is much narrower. When the Earth crosses the center line, that’s a sign that we’re at risk of being hit by the parent comet itself, if both it and us occupy the same space at the same time. (NASA / JPL-CALTECH / W. REACH (SSC/CALTECH))

Cometary debris spreads out along its orbit, creating meteors upon encountering our atmosphere. …


Image for post
Image for post
Although our planet is thought to have had about a 2:1 ratio of oceans to continents throughout its history, there was a period from about 2.4 to 2.1 billion years ago where the surface was 100% covered in ice: a Snowball Earth scenario. Could our planet, despite global warming, actually become cooler over the next 20,000 years? (NASA)

Sure, we’re warming now. But will this continue, or will natural factors change things?

According to our best understanding of Earth’s climate, the global average temperature has increased significantly over the past ~140 years: the amount of time for which a reliable, direct temperature record exists. …

About

Ethan Siegel

The Universe is: Expanding, cooling, and dark. It starts with a bang! #Cosmology Science writer, astrophysicist, science communicator & NASA columnist.

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store