Given the date today, I had to be careful. Is the Royal Institution investigating quantum astrology? No, but those Brits can be quite cheeky.

When I saw this headline, Lasers could ‘cloak Earth from aliens’ on the BBC website, I thought they might be having a laugh. The alternative was a bit of hyperbole in science news reporting, which is a daily occurrence. The paper on which the item is based was officially published on March 30, so I think it’s legit.

What’s going on here is that two astronomers, David M. Kipping, and Alex Teachey, did a thought experiment – what would it take to disguise the Earth from aliens using the transit method to discover the Earth?

Would it Work?

Kipping and Teachey write:

We estimate that humanity could cloak the Earth from Kepler-like broadband surveys using an optical monochromatic laser array emitting a peak power of ∼30 MW for ∼10 hours per year. A chromatic cloak, effective at all wavelengths, is more challenging requiring a large array of tunable lasers with a total power of ∼250 MW. Alternatively, a civilization could cloak only the atmospheric signatures associated with biological activity on their world, such as oxygen, which is achievable with a peak laser power of just ∼160 kW per transit.

One of the methods for discovering exoplanets – planets orbiting other stars – is to carefully measure the light output of those stars and look for a subtle but clear dip in that output, which can result from a planet passing in front of the star from our perspective. This means that the plane of the alien stellar system would have to be aligned with our direction of viewing. This is called the transit method.

Astronomers then have to wait for the dip to happen again, so that they can confirm it is real and periodic, and then they also know the period of that planet. An alien viewing Earth, for example, would have to wait exactly one Earth year to see the second dip.

The Kepler telescope uses this method and has discovered many exoplanets this way. They are mostly very close to their stars, because a planet far away would take many years to complete an orbit, and so there hasn’t even been enough time for Kepler to confirm any such signals.

Incidentally, the two other methods astronomers use to detect exoplanets are by examining the path the stars take in the sky and direct observation.  Large planets cause their parent stars to wobble noticeably. Large planets that are far enough away from their parent stars can also be directly observed from the reflected light, once the light from the parent star is masked out.

What Kipping and Teachey are proposing is that we can use a powerful laser to mask the dip in the total light output of our sun as the Earth passes in front of it. The laser would essentially replace the amount of light blocked by the Earth.

It is important to note, however, that the method they describe would only work for one target star. The 10 hours per year applies to a single direction only. Obviously, there are stars in every direction from the Sun, and any of those stars could harbor curious aliens trying to find Earth. It seems to me we would have to continuously fire that laser, pointing it away from the sun.

I suppose if we discovered radio signals coming from a star that is in the ecliptic, we could hide from those particular aliens using this method.

Another way to look at this is – aliens could be using a similar method to hide from us.

But Should We?

The obvious question here is – why bother? I think there are two main components to this question: should we fear aliens, and is such a method likely to be effective against aliens that we should fear?

I think that any alien race that would threaten the Earth would have significantly advanced technology. Interstellar travel is no easy task. It may take technology thousands of years advanced beyond where we are now. Such a race probably won’t be fooled by our wee laser. They would likely have detection methods we haven’t even considered yet, or would have ridiculously powerful telescopes.

In fact, by shining such a laser we might be just advertising both our presence and our paranoia to those aliens. That might just make them more curious.

Also, because interstellar travel is difficult and would likely take a really long time, I don’t think we have much to fear from such aliens. It would likely take them thousands of years to get here. Why would they bother?

If they have the equivalent of warp drive and can get here in a matter of days, then again, they will laugh at our pathetic laser cloak.

Let’s say they are using self-replicating machines to expand into the galaxy. Once again, those machines will find their way here and the cloaking will not matter.

The other question is whether or not aliens would likely be hostile. The BBC article writes:

They fear that if aliens did visit us they might not be very friendly, and could introduce disease.

Poppycock and balderdash. First, any alien biology would likely not be compatible with Earth biology and so their infectious agents would not be able to infect us. Dog viruses generally cannot infect humans, alien viruses would have no chance.

The only real threat would be from a “The Thing” type of alien biology that does not so much infect as take over our biology. Hopefully, this is unlikely. I would more fear their nanotechnology.

If aliens capable of reaching Earth wanted to conquer us, it would be instantly game over. No “Independence Day” victories, or “War of the Worlds” last minute reprieve. They would introduce their nanomachines and terraform the Earth, and us with it. Their technological advantage would be insuperable.

This might sound like an argument for hiding, but see above. Any aliens that could get to us and threaten us, we likely cannot hide from.

I don’t know how to estimate the probability of and advanced alien race being benign vs hostile. We simply have no data, and any speculation is hopelessly biased by our own idiosyncratic experience. We just have to hope they would be benign.

The real calculation we have to make is this one – what is the probability that we will save ourselves from being wiped out by hostile aliens because we employed a method of hiding from them? I think the answer is – essentially zero.

What is the probability that we will hasten our death by advertising our presence? Again, I think the answer is close to zero.

What is the probability that we will make radio contact with aliens that are either benign or effectively isolated from us by the vast distances of interstellar space? I think this is greater than zero.

So, in the end I think we should advertise our presence and hope for the best. The potential benefits outweigh the risks. We need to be like the Whos in Whoville and shout, “We are here,” to any aliens out there.