StarDate

Based on the number of novels, movies, and TV shows about it, you might assume that traveling through time is as easy as ambling through the park on a sunny day: Just build a TARDIS or soup up your Delorean and off you go on new adventures in time and space.

Time Lords may be to travel through time at will, but the rest of us are limited by the laws of physics [BBC]Alas, the arrow of time moves in only one direction. It allows you to travel into the future, but road blocks seem to prevent any method that scientists can envision for traveling in the other direction.

Wormholes, for example, are theoretical “tunnels” through space and time that seem to allow travel to other times — past or future. But there’s a problem: The wormhole may collapse as soon as anything enters, whether it’s a person, a spaceship, or even a radio transmission.

Another possibility for traveling into the past is moving really fast. Albert Einstein’s theories of relativity suggest that anything moving faster than light might move backward in time. In this case, though, any physical object moving at lightspeed would become infinitely massive. That means you’d need an infinite amount of energy to reach lightspeed — and even more to go faster.

A couple of decades ago, Stephen Hawking suggested that the universe doesn’t like time travel. He wrote that the laws of physics may stop anyone from ever building a time machine — keeping the past safe from its own future.

Even so, physics provides some tricks that allow travel to the future. We’ll have more about that tomorrow.

Script by Damond Benningfield, Copyright 2015

A popular phrase these days is “going forward” or “moving forward.” “Going forward, our team must play better,” or “Moving forward, I think I’ll have the pancakes.” It implies that the speaker somehow has a choice — that he or she could move backward instead of forward. But the universe doesn’t work that way. As far as we know, time moves in only one direction — it follows the “arrow of time.”

That’s something we see in both our everyday lives and in the universe as a whole. We can pour milk, flour, and eggs in a bowl, then mix them up to make pancake batter. But we can’t unmix the batter to make milk, flour, and eggs. In the universe, a massive star explodes as a supernova, but its remnants don’t spontaneously come back together to make a massive star.

That concept is known as entropy, which says that everything evolves from neat and orderly to messy and disorderly. So a set of billiard balls starts out in a neat arrangement, then scatters around the table as you play the game — never the other way around.

Scientists spend a lot of time trying to explain why time’s arrow moves in only one direction. Most of the laws of physics work fine whether time moves forward or backward. And in most cases, when the laws of physics allow something, it happens. There are several possible explanations, but, so far, nothing that’s stuck.

So going forward, there’s still a lot of work to do to explain the one-way arrow of time.

More about time tomorrow.

Script by Damond Benningfield, Copyright 2015

The Moon glides up on the bright eye of the bull tonight. Aldebaran is close to the left of the Moon as night falls. Later, the gap between them will close, as the Moon moves toward the bright star. And as seen from California and Hawaii, the Moon will catch Aldebaran and pass in front of it, blocking it from view in the wee hours of the morning.

It’s hard to notice through the glare of the Moon, but Aldebaran shines bright orange. The color is an indication of its surface temperature, which is much cooler than the Sun. Because of that, Aldebaran is designated as class K.

Astronomers use seven letters to classify true stars — O, B, A, F, G, K, and M.

O stars are the hottest. They blaze tens of thousands of degrees hotter than the Sun, so they shine blue-white. They’re also among the biggest, heaviest, and brightest of all stars.

At the other end are the M stars, which are the coolest. They look orange or red. Almost all M stars are so small and faint that they’re invisible to the unaided eye. But some are bloated and brilliant — stars that have swelled to giant proportions at the ends of their lives.

The Sun is class G. It’s bigger and heavier than most stars, but nowhere near the monsters at the top of the classification scheme.

As it nears the end of its life, though, the Sun will look much like Aldebaran does today — a bloated orange giant, designated as either K or M — at the red end of the stellar classification system.

Script by Damond Benningfield, Copyright 2015

Astronomers have seen planetary systems in just about every stage of formation. They’ve seen the raw ingredients: disks of gas and dust around a parent star. They’ve seen them in the oven: swarms of comets and asteroids built from the raw ingredients. And they’ve seen the fully baked products: planets.

And last year, they revealed the discovery of another stage in that baking process: M&M-sized nuggets that will smash together to make larger bodies.

The nuggets are in DG Tauri, a star system in the constellation Taurus. It’s about 450 light-years away. And it’s only a couple of million years old, so there probably hasn’t been enough time for planets to form.

Using a network of radio telescopes in England, though, a team of astronomers found a possible planet in the making. It consists of a ring of pebbles that are at least a centimeter wide. The pebbles probably assembled from dust grains around the newborn star. The pebbles may eventually merge to form bigger bodies — the size of comets and asteroids. Those bodies may then come together to form a planet.

The ring of pebbles is about as far from DG Tauri as the giant planet Jupiter is from the Sun. So it’s possible that in a few million years, a fully cooked giant planet may encircle the young star.

And Taurus spreads out above and to the left of the Moon this evening. The Moon will pass close to the bull’s brightest star, Aldebaran, tomorrow night. More about that tomorrow.

Script by Damond Benningfield, Copyright 2015

Orion is known for some of the brightest stars in the night sky. Betelgeuse, Rigel, the three stars of Orion’s Belt, and several others are all supergiants — massive stars that were born in the last few million years. And the process of starbirth continues across much of the constellation — some of it in one of the most famous dark regions in the night sky.

The Horsehead Nebula stands close to the star at the left end of Orion’s Belt. The nebula forms the silhouette of a horse’s head against a faintly glowing background — a spray of hydrogen gas energized by radiation from another bright star.

The Horsehead itself is a cloud of much colder, denser gas and dust in front of the glowing background. Because it produces almost no visible light, it forms a dark silhouette.

But within its billowy curtains of gas and dust, the Horsehead is giving birth to new stars on its own. The brightest is at the top of the horse’s head. It’s emerging from a cocoon of gas and dust, and its energy and winds are eroding the material around it.

Many other newly forming stars inside the Horsehead are visible at infrared wavelengths, which penetrate the dust. They, too, are eroding their birthplace. As a result, the Horsehead is falling apart. Over time, it’ll fragment into smaller pockets of darkness, destroying the silhouette of the horsehead. And within about five million years, it’ll completely disintegrate — replaced by the glow of many newborn stars.

Script by Damond Benningfield, Copyright 2015

CREECH-EAKMAN: We should be able to look around black holes in other nearby galaxies and start to understand what’s happening in the very near region close to the black hole.

Michelle Creech-Eakman is one of several people leading the development of an unusual new telescope. Known as the Magdalena Ridge Observatory Interferometer, it will consist of 10 individual telescopes. Astronomers will combine their light to provide extremely sharp views of astronomical objects — sharper than any other telescope to date. And it’ll see fainter objects than any other optical interferometer.

With that clarity, astronomers will probe the regions around newborn stars, where planets are taking shape. They’ll look at old stars, which pulse in and out like beating hearts — and see the “beats” for the first time. And they’ll see how these stars surround themselves with clouds of dust.

And they’ll study the hearts of nearby galaxies that contain supermassive black holes, examining the environment around the black holes with unprecedented clarity.

CREECH-EAKMAN: We will be able to look at about 150 of the closest external galaxies that have these massive black holes. We should start be able to say something about the way the clouds are distributed around the black hole. We won’t ever be able to see the black hole itself, but we’ll be able to see the larger-scale structures. So that will be fun.

The first individual telescope will begin testing this spring, with two more telescopes following in the next few years.

Script by Damond Benningfield