Why Is It So Dark in Outer Space?

iStock/blackdovfx
iStock/blackdovfx

by Kenny Hemphill

Interstellar. Gravity. 2001: A Space Odyssey. Even Star Wars. They all have one thing in common: Beyond the lights of their spacecrafts, and aside from the faint needlepoint glow of distant stars, space is oil-slick dark.

Why that should be so is a question scientists have been asking for more than 400 years. Everyone from Johannes Kepler to Edmond Halley has had a go at trying to figure it out. But it was German astronomer Heinrich Wilhelm Olbers who gave his name to the paradox of the dark sky. Olbers wondered: If the universe is infinite, and there are an infinite number of infinitely old stars, why isn't the light from those stars visible from Earth? If it were, the night sky would be bright, not dark.

By the end of the 19th century, the idea of an infinite universe had been largely abandoned—something which was anticipated by Edgar Allan Poe in his 1848 essay, Eureka, where he wrote:

"Were the succession of stars endless, then the background of the sky would present us a uniform luminosity, like that displayed by the Galaxy—since there could be absolutely no point, in all that background, at which would not exist a star. The only mode, therefore, in which, under such a state of affairs, we could comprehend the voids which our telescopes find in innumerable directions, would be by supposing the distance of the invisible background so immense that no ray from it has yet been able to reach us at all."

In other words, Olbers' Paradox is resolved with the assumption that the universe has a finite age (something which is supported by the Big Bang Theory), that the speed of light is finite, and thus the observable universe has a horizon beyond which we can't see the stars. Fifty years later, Lord Kelvin used math to prove that in a finite universe, or one in which stars were born and died, the night sky should be dark.

There are other contributing factors to the darkness out there. Cosmic expansion over billions of years means that the energy from the radiation which was emitted following the Big Bang has been red-shifted, or reduced to the low temperature of microwaves. That puts it beyond the visible spectrum. And other radiation in space—infrared and ultra-violet light, radio waves, and X-rays—are all invisible to the human eye. If we could see them, space would seem a little less dark.

Universe Today has another explanation: "Space is black to our perception because there are few molecules of matter that can reflect or scatter light like our atmosphere on Earth. Since light goes in a straight line it seems to be absorbed by the void and vacuum of space. Otherwise space would look similar to the sky on Earth."

Think of a flashlight in a dark room. Look directly at the bulb and you see its light. Point it at furniture or a wall, and you see the light reflected. If there was nothing to reflect it, you wouldn't see any light at all. Which is exactly what happens in space.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

What's the Difference Between Stuffing and Dressing?

iStock
iStock

For carbohydrate lovers, nothing completes a Thanksgiving meal quite like stuffing—shovelfuls of bread, celery, mushrooms, and other ingredients that complement all of that turkey protein.

Some people don’t say stuffing, though. They say dressing. In these calamitous times, knowing how to properly refer to the giant glob of insulin-spiking bread seems necessary. So what's the difference?

Let’s dismiss one theory off the bat: Dressing and stuffing do not correlate with how the side dish is prepared. A turkey can be stuffed with dressing, and stuffing can be served in a casserole dish. Whether it’s ever seen the inside of a bird is irrelevant, and anyone who tells you otherwise is wrong and should be met with suspicion, if not outright derision.

The terms are actually separated due to regional dialects. Dressing seems to be the favored descriptor for southern states like Mississippi, Tennessee, South Carolina, and Georgia, while stuffing is preferred by Maine, New York, and other northern areas. (Some parts of Pennsylvania call it filling, which is a bit too on the nose, but to each their own.)

If stuffing stemmed from the common practice of filling a turkey with carbs, why the division? According to HuffPost, it may have been because Southerners considered the word stuffing impolite, and therefore never embraced it.

While you should experience no material difference in asking for stuffing or dressing, when visiting relatives it might be helpful to keep to their regionally-preferred word to avoid confusion. Enjoy stuffing yourselves.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

Why Do Tires Have to Be Filled With Air?

BookyBuggy/iStock via Getty Images
BookyBuggy/iStock via Getty Images

Paul Misencik:

This is an issue that has perplexed me for most of my life, because pneumatic tires filled with air seem like the last anachronistic, 19th-century component of a modern automobile, and an idea which should have disappeared many decades ago. In an era where even the internal combustion engine itself is giving way to electric motors, and where a new economy hatchback has exponentially more computing power than the Space Shuttle, pneumatic tires don’t seem to make sense any longer.

(And before I get flamed, I know modern tires are vastly more advanced and reliable and capable than their 1930s counterparts. Blowouts, which were a common occurrence when I was a kid, are pretty much unheard of today. Modern tires are great, but they are still vulnerable and maintenance-intensive in a way that doesn’t make any sense to me.)

Companies have experimented with non-pneumatic passenger vehicle tires in the modern age—one of the primary drivers was Michelin. But the tires weren’t filled with solid rubber. In fact, they didn’t even have sidewalls. They were open on the sides, and they had a support lattice of structural polyester ribs, with a ton of air space between the contact patch and the (now deformable) wheel.

One of the big problems with switching from pneumatic tires to non-pneumatic tires is the fact that the current air-filled tire is an important component of the suspension of a vehicle. The flex in the sidewall is a critical part of the compliance of the suspension and substantially affects a vehicle's ride and handling. (Which is why race car drivers sweat tire pressures at each corner of the vehicle so much, as even a small change in tire pressure can have a big effect on the handling and grip of a vehicle.)

If a company like Michelin wants to make a non-pneumatic tire, they'll improve their chances of finding success with it if the new design mimics the compliance and flex characteristics of the outgoing, air-filled models as closely as possible. That way, Michelin would be able to sell the new, non-pneumatic design as a retrofit to older vehicles whose suspensions were originally designed with pneumatic tires in mind. And that is hugely important because if they can’t, it becomes much more difficult to convince manufacturers to change over to the new design—particularly after the mild debacle of Michelin’s failed “TRX” metric tire idea of the 1980s, which required the use of a special wheel and which, despite being by most accounts a superior design in almost every way, never really took off. (Owners of 1980s Ferrari 512 Berlinetta Boxers and some Saab 900 turbos will know what I’m talking about here.)

Non-pneumatic Michelin tires are also rather weird looking, and it’s not clear which manufacturers, if any, would take the risk of being the first to offer them on a new car.

So that is the real issue: Any non-pneumatic tire design must be not only clearly superior to the pneumatic designs of the past, but it must be functionally identical to the outgoing models they would replace, and they must be visually acceptable to consumers.

I hope it happens, though. I hope someone cracks the nut. Pneumatic tires are a 19th-century application still being used on 21st-century vehicles, and at some point that needs to change.

This post originally appeared on Quora. Click here to view.

SECTIONS

arrow
LIVE SMARTER