# What's the Speed of Dark?

Welcome back to Giz Asks, a series where we ask experts hard questions about science, technology, and humanity’s future. Today, we’re wondering about the “speed of dark,” and for that matter, the scientific nature of “speed” and “darkness.”

# How Is It Possible That Galaxies Are Moving Away From Us Faster Than the Speed of Light?

According to Albert Einstein, the speed of light is an absolute constant beyond which nothing can move faster. So, how can galaxies be traveling faster than the speed of light if nothing is supposed to be able to break this cosmic speed limit?

# Researchers Slow The Speed Of Light As It Travels Through A Vacuum

Normally, light zips through a vacuum at a blazing 186,282 miles per second. But as a new experiment by Scottish physicists has shown, this isn't always necessarily the case.

# How much stuff is in a light-year?

Imagine taking the distance that light travels in an entire year. Now turn that distance into a cube, each side one light-year across. How much "stuff" would be in there? And how empty would it be? It all depends on where you put your massive cube.

# How Fast Things Travel Compared to the Speed of Light

Sometimes it's hard to put things like the speed of light into perspective: it's a number so large that it's tough to make sense of. Which is why this visualization, which compares the speed of things you can (kinda) more easily visualize, is massively helpful.

# How the Speed of Light was First Measured

The speed of light in a vacuum stands at “exactly 299,792,458 metres per second“. The reason today we can put an exact figure on it is because the speed of light in a vacuum is a universal constant that has been measured with lasers; and when an experiment involves lasers, it’s hard to argue with the results. As to…

# How Scientists Stopped Light Dead For a Whole Minute

Of all the things you might choose to halt in its tracks, the world's fastest—light—might not be at the top your list. Clearly, you don't have the ambition of the team of scientists who just managed to stop it dead—for a whole minute.

# How Someone Measured the Speed of Light by Accident

At a time when many thought the Speed of Light was infinite, a few brave souls tried to come up with a definite number for it. Most of them failed. There was one guy, however, who wasn't even trying, but came up with a great way to guess. Take a look at how he took his measurement, and what it has to do with the moons…

# How much does a shadow weigh?

Then again, a better question might be "how much less does an area covered in shadow weigh relative to surrounding areas covered in light?"

# Faster-Than-Light Travel May Be Possible

According to Einstein's special theory of relativity, light traveling in a vacuum is the universal speed limit. But scientists love to try and break rules—and now a tweaked version of Einstein's equations suggests that faster-than-light travel might just be possible.

# How to Break the Speed of Light in Your Backyard

Nothing can travel faster than the speed of light, right? Wrong! I think. Honestly, all I'm positively sure of after watching this mind-bending One Minute Physics lesson is that I need to go point a laser at the moon asap.

# What would the world look like if you approached the speed of light?

This truly awesome video has the answers to that question. It imagines a trip down a desert highway at speeds approaching light, and then shows all the weird and wonderful optical effects the theory of special relativity says we'd experience.

# The wheel that reveals the speed of light

Is there anything a wheel can't do? The Fizeau Wheel helped calculate the speed of light itself.

# What is the speed of smell?

The speed of light is 186,282 miles per second. The speed of sound is 761.2 miles per hour. That takes care of vision and hearing, but what about our other senses? Shouldn't there be a speed of smell?

# New experiment shows that time travel is even less likely than we thought

A recent experiment stomps on the dreams of many theoretical physicists, hopeful children, and Star Trek IV fans. After a series of tests that suggested we might discover a theoretical form of time travel, scientists hit a brick wall. Or they had hit a brick wall. Or perhaps they will. Tough to get time travel grammar…

# The speed of light could turn the middle of the ocean into a stock-trading center

When the world's financial giants begin creating vast artificial islands in the middle of the oceans to use as the hubs of stock-trading, it'll all be because of the speed of light.

# Spacetime invisibility cloaks can hide entire events inside temporal voids

Invisibility cloaks are taking baby steps from science fiction to science fact. But there's an even stranger and more incredible possibility - an invisibility cloak that works in both space and time, shielding whole events from history itself.

# Three "Simple" Ways to Become a Chrononaut

In his eponymous Discovery Channel series, Stephen Hawking says that time travel is totally theoretically possible. Here are the three most straightforward ways to achieve it.

# Why Are Scientists Trying To Create Slow Light?

Achieving faster than light speed is one of the dearest dreams of science (and science fiction). But what about slowing light down? In the last ten years, scientists have done some amazing things by slowing down the speed of light.