"No science, no Twitter": Scientific research led to the computer technology that makes President Donald Trump's favorite social network possible.

A quote from astrophysicist and Cosmos TV show host Neil DeGrasse Tyson was popular on signs and T-shirts: "The good thing about science is that it is true whether or not you believe in it."

"This sign is flat -- the Earth is not!" said one marcher, urging people not to regress to an obsolete world view science helped overturn.

Darcy's law governs the rate liquids flow through a medium, like water through soil or oil through rock.

A marcher pays tribute to the contribution her father, Vernon Rossow, made to aerodynamics and aircraft safety.

"Tribology not tribalism," one marcher's sign read. Tribology is "the study of friction, wear, lubrication, and the design of bearings," according to Wikipedia.

A Star Wars reference to basing conclusions on data: "The empiricist strikes back."

One recurring theme: Truth, as discerned by science, ultimately can't be denied: "Climate change exists whether you believe it or not."

"Data over dogma."

Computer science humor deals with the tricky problem of concurrency, in which a computer manages several related tasks simultaneously: "Who are we? Computer scientists! What do we want? Now! When do we want it? Concurrency!"

A mathematical joke: the square root of negative one is denoted as i -- the basis for imaginary numbers. In other words, "Alternative facts are imaginary."

A remark about political priorities: "Less invasions, more equations."

A jab at Donald Trump's assertion that global warming is a Chinese hoax.

"Without data, you're just another person with an opinion."

A polar bear, a victim of global warming, offers a rude gesture.

"More science, less fiction."

"God wants scientists. If we entertain the 'God hypotheses' we must examine all His evidence." The back of this sign said, "He left all those clues to find."

"Do not turn my students' favorite dystopian ficiton into coming-of-age novels."

An objection to EPA Administrator Scott Pruitt, who doubts the scientific consensus about climate change: "Liar liar, planet on fire!"

"Didn't die from the plague? Thank a scientist."

A patriotic message: "Keep America great -- invest in science."

Pussy hats from the women's march earlier this year have morphed into pussy brain hats for the March for Science.

A dog's shirt reads, "Let's paws for a moment of science."

San Jose police were on hand to manage traffic and crowds, but people in the march shuffled along smoothly.

"I need science because I need health care, hope, a cure," said a sign calling for research on an affliction called Ehlers-Danlos syndrome.

"Raise a glass to freedom," one sign said, showing a classic Erlenmeyer flask used in chemistry and other research.

"I'm with her. Thinkers not deniers."

A quote from famous scientist and science communicator Carl Sagan: "It pays to keep an open mind, but not so open that your brains fall out."

The Monterey Bay Aquarium supported the March for Science.

"Public policy based on rigorously established objective evidence now!"

"Science saves lives."

A man in a lab coat and safety goggles holds a sign: "Science separates fact from fiction."

A common sign: "Science is not a liberal conspiracy."

Most marchers spoke in favor of science, but some were out to protest President Donald Trump and his administration.

The March for Science took place during Silicon Valley Comic Con, so there was some mixing of cultures at the end. Here's a male version of comic book character Harley Quinn.

"Climate change is real, alternative facts don't exist in science, keep your tiny hands off our data, America became great with the help of science."

"Teach your kids about science before a politician does."

"Evidence trumps ignorance."

Heisenberg uncertainty principle humor: "It's impossible to locate a good quantum mechanic."

The March for Science took place on Earth Day, so many signs had an environmental theme like "May the forest be with you."

A crowd of people in the San Jose, California, March for Science.

"Read a science book, you moron."

Hear what Bill Nye has to say about climate-change deniers in his interview with CNET. He stopped by to promote the launch of his new Netflix show, "Bill Nye Saves the World." (See video below.)

"EPA is not a 4-letter word."