Three centuries after his death, Sir Isaac Newton still keeps us from travelling to the stars.
Or at least his laws of physics do.
Remember that big space rock called Oumuamua that flew through our neighbourhood in the summer? Astronomers nearly didn’t see it; rocks are dark blobs against a black sky, and a telescope only spotted it as it flew back toward the edge of our solar system and presumably beyond.
For a brief moment in early November, though, some eggheads at Harvard University saw it speeding up when it had no business speeding up and wondered: What if it’s an alien ship?
Consensus today among people who study these things: It almost certainly isn’t. But it got everyone talking about whether aliens from another solar system could fly here — or what it would take for humans to fly to a distant, inhabited planet.
That was Newton’s time to bring everyone down to Earth.
We asked some astronomers about it.
“We believe that every star in our galaxy has a planetary system,” said Paul Delaney of York University. That belief is the result of years of observations, especially by the Kepler Space Telescope launched in 2009. About 15 to 20 per cent of these have planets that could support life, meaning there are tens of billions of Earth-like planets in the Milky Way.
Geography gets in the way, though. The problem is all about distance.
There are 11 stars within about 10 light years of Earth. (A light year is the distance light travels in one year, or nearly 9.5 trillion kilometres.) The closest is more than four light years away, so it’s going to be a long trip.
“At best it’s going to take you years to go between the stars, and that’s if you get up close to the speed of light,” Delaney said. Light travels about 300,000 kilometres every second.
What does it take to speed up a spaceship?
“Lots and lots of energy. We’ve got nothing even remotely capable of doing that,” he said.
Blame Newton. First for his first law of motion: Any object has inertia; it will only accelerate if an external force acts on it. Add some more Newtonian physics: The more mass an object has, the more force required to speed it up.
Even “space chips,” or wafer-sized space probes weighing a few dozen grams, requires more energy than we know how to produce in order to reach a speed that would carry them to a star in a reasonable time.
“And don’t forget relativity,” Delaney said. “The closer you get to the speed of light, the larger is your inertial mass, which means even more energy is required.
“We are really pretty bereft of options (for) big objects being accelerated up to serious speed to make them travel interstellar distances.”
Space travel “is not really difficult to do it if you’re willing to wait. If you want to do it in the lifetime of a Homo sapiens, it’s a lot more difficult,” said Seth Shostak, a senior astronomer with the Search for Extraterrestrial Intelligence (SETI) in California.
A typical NASA Mars probe, if launched from the nearest star, “would take about 75,000 years to get here (and) by that time your own society is probably so different that you have forgotten entirely about having done it.”
To send one ship to a nearby star within a century, “you’re talking about the energy expenditure comparable to what Canada uses in a few centuries.”
Still, Delaney and others were thrilled to learn about Oumuamua “from the moment you say ‘interstellar visitor,’ even if it is probably a rock.”
“All of us have a little bit of wishful thinking,” Delaney said. But evidence? Not so far.
But he is not looking for aliens. Rather he is looking at the big rock as a special delivery of the building materials from which another solar system is made.
Meanwhile the bigger question for Shostak is: Why would aliens pay attention to Earth at all, let alone travel here? “Because, if they are that far away, what do they know about Earth?” Only that we have oxygen in our atmosphere and, therefore, life of some sort.
Radio signals — especially airport radar, which is a very good frequency for reaching into deep space — have been going out for about 70 years. Most of the universe hasn’t received those signals yet.
Yet Shostak remains a believer in alien life, somewhere. Calculating roughly a trillion planets in our galaxy, the Milky Way and a trillion other galaxies, he figures it would take a miracle for Earth to be the only place with life, and he doesn’t believe in miracles.
In the meantime, an astronomer at Massachusetts Institute of Technology has proposed shining a million-watt laser beam into space as a “porch light” to let everyone know that Earth is occupied.
James Clark figures anyone within 20,000 light years would notice.
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