Skepticism about Alien Visitors

There've been numerous reports of UFOs in the news and lots of speculation that these objects are alien visitors from some other planet. I've been very skeptical of the theory that extraterrestrials are visiting earth given the extreme unlikelihood that any other planet in the galaxy (and maybe in the entire universe) would possess the suite of properties that would enable it to produce and sustain intelligent life and given the vast distances any intelligent life, were it to exist, would have to traverse to get here.

Physicist Eric Hedin has an interesting piece at Evolution News in which he reverses the problem of traveling across these enormous distances by highlighting the difficulties that would have to be overcome in order for a traveler from earth to reach any other planet in our galaxy.

He writes:

What about the alluring hope of future generations of humans traveling across the interstellar oceans of space to establish Earth outposts on such extrasolar planets? Astronomers have determined [that there]... are roughly 2,000 stars within 50 lyrs [light years] of Earth, compared to approximately 200 billion stars in the Milky Way galaxy (one millionth of one percent lie within 50 lyrs of Earth).

We can set some boundaries on the feasibility of interstellar space travel (either for humans or putative aliens) by applying the known laws of physics.

Using special relativity, let’s imagine what it would take in terms of raw energy to accelerate a spaceship to the speed necessary to make a 40 lyr journey (say to Gliese 12b) in 5 years as measured by the astronauts onboard.

First, we need to find the speed, relative to Earth that this spaceship would have to attain to generate the proper time dilation for the astronauts to arrive in 5 years by their clocks. A bit of algebra with Einstein’s time dilation formula yields a required speed of 0.99c, where c=300,000 km/sec is the speed of light through vacuum.

Since time flows at different rates for the reference frame of Earth compared to the reference frame of the spaceship moving at 0.99c, we find that the journey which takes 5 years for the astronauts takes 40.3 years according to observers back on Earth. This would be somewhat inconvenient, but perhaps manageable.

But when we calculate the energy required to accelerate a modest-sized spacecraft, outfitted with everything that a team of astronauts would need for a multi-year expedition to explore an unknown destination, we find that the answer is daunting.

Using Einstein’s special relativity formula for kinetic energy, and assuming a mass for the spaceship equivalent to that of a fully loaded 747 aircraft (m=400,000 kg), we find that the energy needed to accelerate the spaceship to the cruising velocity of 0.99c is 70 quadrillion kWh [kilowatt-hours].

Assuming that the astronauts want to stop at the distant star system, we’ll need to double this amount to account for deceleration, for the spaceship to make the one-way journey from Earth to the distant star.

So, just how much energy is 140 quadrillion kWh? Believe it or not, it’s equivalent to 4,800 times the total energy consumption of the United States in the year 2022. This means all the electricity, petroleum, natural gas, and any other form of energy used to power everything in the U.S. for one year would be 4,800 times too small to get our modest-sized spaceship to a relatively nearby star in a reasonable amount of time.

I think it’s fair to say that interstellar space travel isn’t even remotely possible with our current understanding of physics and technology.

Hedin goes on to explain that even were the size of the spaceship reduced or the craft were to use matter annihilation as an energy source the difficulties would still make such a voyage physically impossible.

What would we need to trim this daunting energy requirement down to size? Reducing the mass of the spaceship doesn’t exactly solve the problem. Suppose we trade our 747-sized spacecraft for an economy model about the size of a Winnebago camper trailer, having a much smaller mass of 4,500 kg. That’s 89 times less mass than the original spacecraft.

Unfortunately, this means that the energy required to get there is still 54 times the total U.S. energy consumption for an entire year.

OK, so we just need a lot of energy, and apparently nothing we currently use for generating energy will come even close to meeting our needs for interstellar space travel. But what’s to say we couldn’t develop a super-charged energy supply? The gold standard for producing energy from mass comes from the total annihilation of matter, converting it 100 percent to energy according to Einstein’s famous equation, E=mc2.

How much mass, then, would we need to convert to pure energy to meet our original estimate of 140 quadrillion kWh? The answer turns out to be a little over 5.6 million kg of matter. That’s about 14 times more mass than the mass of the fully-loaded 747-sized spacecraft.

He has more at the link, but you get the picture. Space travel to even the closest planet outside our solar system is entirely impractical given our current knowledge and technology and thus the likelihood of aliens visiting us is exceedingly low.

But someone may object that these aliens could be technologically so advanced that they've been able to overcome the difficulties. That's possible, of course, but it'd be helpful to be able to give some plausible answer to two questions: What are the odds that another life supporting planet exists within our galaxy? And what are the chances that that planet gave rise to intelligent creatures who have mastered an incomprehensible (to us) technology?

My opinion is that the probabilities, when all the variables are taken into account, would be astronomically low. Anyway, Hedin has more on this topic at the link.