Breakthrough Starshot plans to send spacecraft to the nearest star within your lifetime.

Is this for real?

Does this mean it's the future, finally?

[music playing] Do you remember when the future had spaceships?

I grew up in the afterglow of the Apollo program, in the era of the space shuttle.

We were so sure that these were just steps on the inevitable path to our exploration of the galaxy.

We've been waiting so long now that this surety of a space-faring future has started to slip into the realm of science fiction.

But the wait may be over.

Billionaire physicist Yuri Milner recently announced the Breakthrough Starshot program.

The plan?

To send swarms of light sail driven nanocraft to Alpha Centauri fast enough that we may have close-up images of alien worlds within our lifetimes.

Today, I want to take this idea apart to look at the details of the plan, what it will teach us about the universe, and whether we can actually do this thing.

But first, a big told you so is in order.

We totally called this in our episode on the possibilities of interstellar travel.

Looks like light sails will be the first propulsion tick to get an unmanned probe to the stars.

OK. Let's review the essential awesomeness of light sails.

They do exactly what they say.

A spacecraft is propelled as the light from the sun-- or from a giant laser-- accelerates a sail of reflective material.

The advantage of light sails lies in the fact that they don't have to carry any propellant.

Even for next generation fuels, like certain types of fusion, the propellant weight can be most of the craft weight at launch.

So the fuel is mostly accelerating itself.

Light sails need no onboard propellant and the power generation stays back at home, whether it's the sun or an Earth-based laser.

So why haven't we done it yet?

Oh, we have.

The Japan Aerospace Exploration Agency, JAXA, flew the first interplanetary light sail in 2010, Ikaros.

This solar sail has buzzed past Venus and now explores the interplanetary space in an orbit between Earth and Venus.

Solar sails work well within the solar system and there are a number of plans for more of these.

But what about interstellar work?

Well in that case, light from the sun just won't cut it.

Alpha Centauri is 4.4 light years away and so even at a good fraction of the speed of light, it's a many year mission.

Accelerating on sunlight alone would make it a many millennium mission.

The solution is lasers.

The solution is so often lasers.

The first serious proposal along these lines was the Starwisp, proposed by scientist and author, Robert Forward, and updated by Geoffrey Landis.

This would be a kilometers-wide carbon fiber mesh sail propelled by a microwave laser-- a maser, which would be focused by a 1,000 kilometer diameter microwave lens in space.

The Starwisp would accelerate to 10% or so of the speed of light, getting it to alpha [inaudible] barely within the science team's working life.

In a way, Starshot is an update to the Starwisp.

The basic concept is the same-- an extremely low mass laser powered light sail.

The main innovation of the Starshot is that it's not just low mass, it is ultra low mass, weighing in at grams rather than Starwisp's kilograms.

It's being called a nanocraft.

Each Starshot will be comprised of a sail around a meter in diameter that's made of an advanced meta-material-- a nano-fabricated sheet only hundreds of atoms thick.

Graphene is likely to be involved because, let's face it, graphene can do everything.

The payload will be a single wafer of electronics and would include multiple detectors, including a camera, small lasers that work both as thrusters and as communication devices, and perhaps even a small nuclear battery.

Another big difference compared to Starwisp is that Starshot will be powered by a visible light laser, not a maser.

This is important because visible light lasers can maintain a much tighter beam than a maser can.

And when your sail is so small, that's really important.

The ultra low mass means that the nanocraft can be accelerated to a decent clip with a giant laser that we could plausibly build in a generation.

So less vast alien mega structure slash planet destroyer and more Bond super-villain laser.

It would be a ground-based phased array of mini lasers called a light beamer that will produce a combined 100 gigawatt beam.

This thing could burn Yuri Milner's tag on the surface of the moon and also accelerate a Starshot craft to 20% of the speed of light in a few minutes.

That'll get it to Alpha Cen in a little over 20 years but it would get it to Mars in two hours.

Build a laser that big and you want to use it, right?

The plan is to launch not one, but thousands of these craft.

This is critical because there's actually no way for these things to slow down at the other end.

Each craft will have a few minutes to collect data as it zips through the Alpha Cen system, so you really want a long stream of them to collect enough data.

What can a Starshot probe expect to do in those few minutes?

Well take pics, for one.

It's expected that the craft will launch with camera tech capable of resolving continents and oceans on planets orbiting Alpha Cen, assuming they have them.

It will take a 300 kilometer diameter telescope at Earth to get the same resolution.

Some type of color spectral sensitivity may even point to life signatures on these planets.

There's a lot of work to be done.

Miniaturization of payload components isn't quite there yet.

The light sail will need to be insanely thin and almost immune to heating.

Everything will have to withstand tens of thousands of G's of acceleration and impact from interstellar dust or cosmic rays.

The laser propulsion array needs to combine and direct its beams with incredible precision through a turbulent atmosphere.

And at the other end, Starshot probes need to know where to point the cameras and then beam that info back to Earth with whatever energy can be stored on board.

There are no deal breakers here, but some of this technology is a way off.

The program relies very heavily on the projections of Moore's law.

It's assumed that processor size, camera pixel density, laser power to mass ratio, et cetera will continue their exponential improvement.

The hope is to launch in around 20 years.

With a 20 plus year travel time and 4.4 years for the pics to be beamed back to Earth, that gets us the data in 45 to 50 years.

Eat healthy.

Exercise.

And you could well live to see this.

Why should we take this particular idea seriously?

Well to start, it has money.

Milner has shelled out $100 million to get started.

To see completion, it will take several billion, but money has a way of attracting money.

If people take this seriously, then others will get on board.

And indeed they have.

Stephen Hawking and Mark Zuckerberg form the board.

The advisory team includes legendary engineer Freeman Dyson, the UK astronomer royal, Martin Rees, dark energy Nobel Laureate, Saul Perlmutter, and several other very prominent leaders in their scientific and technical fields.

Their email to me got caught in my spam filter, I assume.

What do you guys think?

Is this worth doing?

Is the scientific payoff worth the money or is the awesome factor alone worth the investment?

Is the benevolent billionaire model going to replace national funding for large scale scientific programs and is that even desirable?

And what will the Starshot probe find when it reaches Alpha Cen?

Perhaps a welcome to the galactic community sign?

We'll be sure to get back to you with the first up close alien snapshots in around 50 years right here on "Space Time."

In the last episode, we talked about how dark energy causes this exponentially accelerating expansion of the universe and you guys had a lot to say in the comments.

Satya Prakesh asks a great question.

Which is the first cause?

Does dark energy cause expansion?

Does expansion cause dark energy?

All right.

This is a good one.

Dark energy does drive the expansion rate, causing a sort of anti-gravity effect.

But if dark energy diluted away, like regular matter does, that effect would diminish as the universe expanded.

However, dark energy doesn't dilute.

Its density stays constant.

That means the larger the universe is, the more dark energy there is and so the more of this anti-gravity.

So expansion results in more dark energy and more dark energy results in faster expansion.

It's a positive feedback cycle that leads to exponential expansion.

Scott Mcphee would like to know how it all ends.

Does the universe expand to such a ridiculous size that it's filled ultimately with only stellar remnants and darkness?

Or does space itself rip itself apart?

So that depends on what dark energy actually is.

If it's really fully described by a constant cosmological constant and so has an unchanging density with time, then no, space time doesn't get ripped apart.

The universe expands exponentially forever and eventually the stars die out, the black holes evaporate, and the universe undergoes heat death.

But if the density of dark matter varies with time, then there are a range of possibilities.

The one where space time rips itself apart at a fundamental level, the so-called Big Rip, happens when the density of dark energy increases.

So we'll talk about that in another episode.

Sandeep Siwach would like to know why dark energy only effects the space between galaxies and not within galaxies.

So dark energy only has an observable effect when its density is at least comparable to the density of regular matter.

The density of matter inside galaxies is much, much higher than in between galaxies and even much, much higher than the average for the universe.

There's just not enough dark energy in these regions to do very much.

Accessless points out that we must need some sort of luminosity reference point before we can start using white dwarf supernovae or Type 1a supernovae, the standard candles.

And that's absolutely right.

We need to figure out the luminosities for a good number of these supernovae independently, before we can start using them as standard candles.

We do that by finding independent distances to white dwarf supernovae in nearby galaxies.

There are different ways to do this.

For example, we can use cepheid variable stars, another type of standard candle, to get an independent distance to the galaxy in which a supernova exploded.

Cepheid variables are then calibrated as standard candles based on cepheid's in our own galaxy.

There's a whole sequence of steps we use to calibrate astronomical distance measurements.

It's called the cosmic distance ladder.

Adrian Abdel reminds us that the universe is dark and full of terrors.

Yes, my friend.

And the heat death of the universe is coming.

Ah, valar morghulis.

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