Going to the Stars, Riding on a Beam of Light!

dontstopmeno

What might the universe look like if we were able to ride on a beam of light? Special Relativity puts an upper limit on how fast we can travel and states quite clearly that superluminal travel is not possible.


This wide-field view of the sky around the bright star Alpha Centauri was created from photographic images forming part of the Digitized Sky Survey 2. The star appears so big just because of the scattering of light by the telescope’s optics as well as in the photographic emulsion. Alpha Centauri is the closest star system to the Solar System.

During his years working in the Swiss Patent Office, Albert Einstein often imagined what it would be like to ride on beam of light. This thought experiment would come to play a key role in the development of his Special Theory of Relativity, one of the four great works produced during his 1905 Annus Mirabilis. In a stroke of insight that was nothing short of genius, he saw it all, that as an object accelerated to speeds approaching light speed, that time would slow down, mass would increase and length would contract. In many ways, in what could only be today described, perhaps serendipitously, as insightful or as a prophetic vision of the future, this will be how humanity first goes to the stars, quite literally riding on a beam of light!

Turning science fiction into science fact and as a logical follow-up to the first initiative in the Breakthrough series of projects, Breakthrough Listen, forward-looking Russian investor and science philanthropist Yuri Milner has announced the ambitious $100 million “Breakthrough Starshot” project. Yuri Milner was named in honor of Soviet Cosmonaut Yuri Gagarin, the first human to travel into space and the first to orbit the earth during the historic 1 hr 48 minute Vostok 1 mission. To honor Gagarin, Milner, on the occasion of the 55th anniversary of the historic flight on 12 April, 1961, chose to announce the grant, funding the project.

This latest project follows the Breakthrough Initiative’s Prime Directive, to explore

the big questions of life in the Universe: Are we alone? Are there habitable worlds in our galactic neighborhood? Can we make the great leap to the stars? And can we think and act together – as one world in the cosmos?

Such a mission is only becoming possible now with the concurrent maturation of three technologies: micro electronics, thin-film and nano technologies. A Blue-ribbon panel has been formed as initial collaborators that include such brilliant lights as world-renown Astrophysicist Stephan Hawking, physicist Freeman Dyson and the widow and partner-in-science of the late Carl Sagan, Ann Druyan.

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Hubble Space Telescope image of Proxima Centarui. Notice the decidedly reddish cast to the star.

The general idea behind the Breakthrough Starshot mission is to accelerate a fleet of mini light-sail craft to 20% light speed towards our nearest neighboring star system, Alpha Centauri. Given that the star system is 4.3 light years distant, the one-way trip will take approximately 22 years traveling at 1/5 light speed. Alpha Centauri is really a triple star system consisting of Alpha-Centauri A, an identical star to the sun (G2V), Alpha-Centauri B, a slightly cooler K class star (K1V) and Alpha-Centauri C, a small, cool M class red dwarf star (M6V) also known as Proxima Centauri. The mission narrative indicates the target to be “Alpha Centauri”, not a specific member of the trinary system. It is understood that the target is the entire star system as the known unknowns and the unknown unknowns in the intervening 4.3 light years could conspire to alter the course considerably. One possible target would be the newly discovered Earth-mass planet orbiting the cooler Alpha-Centauri B.

 

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An illustration of a “Worm Hole”, a passage through space-time through which we could pass from one point in the universe to another without violating Special Relativity which puts a strict upper limit on how fast we can physically travel

Much science fiction has been produced surrounding the idea of going to the stars, from Star Trek (The Starship Enterprise) and Star Wars (the Millennium Falcon) both franchises gaining wide popularity, to the movie Contact where Dr. Ellie Arroway (Jodie Foster) travels to the star Vega in a machine designed by the Vegans to create a “wormhole”, a tunnel through which she travels. The “starships” featured in Star Trek and Star wars, cinematic adventures whose scope spans decades, don’t really, physically travel above light speed but “tunnel” through space, much like going straight through a sphere to get to the other side rather than following the curve to that same point. In a clever manipulation/warping of space-time, they effectively go from point A to point B without actually traveling above light speed. Although there is a theoretical basis for the idea, the technology and engineering required is centuries away and may never be possible.

By way of describing the energy required to accelerate a one-gram mass, the scale of the nano craft envisioned in the Breakthrough Starshot project, to 0.2 light speed, one can quickly get a sense of the amount of energy required to accelerate a small, one or two man ship to even 0.1 (1/10) light speed. Kinetic Energy, the energy of motion, varies as the square of the velocity, specifically E(k) = (1/2)M*V². Choosing 0.2 C (C is the universal variable for the speed of light and is equal to 3E8 meters/second), we plug in the numbers and compute: KE = 0.0005kg*(6E7)² = 1.8E12 (1.8 Terra) Joules or 500 mega-watt hours (a sustained 500 megawatts for one hour!) or the entire output of a small nuclear power station for one hour, and that is a one-gram nano ship! With every 10 percent, the energies quickly become enormous! A jump to 40% C would require a quadruple increase in the energy required or 7.2 Terrajoules! An additional problem regarding energy, one we don’t ordinarily encounter in our everyday lives, regards the increase in mass as we approach “relativistic” velocities or velocities that are significant fractions of the speed of light.

Einstein’s Special Theory of relativity clearly sets the speed of light as the universal speed limit where no object with mass (even a tiny electron whose mass is 9.1E-31 kg) can travel at light speed. Special Relativity also describes real, physical effects that occur as an object accelerates towards relativistic velocities. At the speeds we’re used to, even spacecraft in orbit, the effects of Special Relativity are negligible but measurable; many experiments have demonstrated their veracity. As you accelerate, your mass increases, time slows down and your length contracts all according to the value of γ (gamma), computed as 1/sqroot(1-v²/c²). As v approaches c, the entire expression becomes undefined. At 99% light speed, your mass has increased by a factor of 7, time has slowed down by the same factor and your length has been foreshortened, also by the same amount.

Using our basic calculation for kinetic energy and factoring in the 7-fold increase in mass of our one-gram nano craft, the energy required to accelerate it to 99% light speed would be 308 Terrajoules! This is equivalent to 86 gigawatt hours or all the energy produced by the Indian Point Nuclear Power station every 43 hours or the combined energy yield of 6 Hiroshima-class nuclear weapons released all at once!

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Targeting the square meter size light sail attached to the nanocraft, using phased-array, ground-based lasers in the 100 GW range, the nanocraft will accelerate to 20% light speed in 10 minutes within a distance of 2 million kilometers

So, how are we going to do this? In theory, an ultralight, ultrathin “sail” would be attached to the nano-craft and a fleet of them would be launched from an an earth-orbiting platform. Many hundreds, perhaps thousands of nano-craft would be launched with the odds that some of them would survive the (4.3 ly * 5 =) 22 year journey to the Alpha Centauri system. Once released, a concentrated, phased-array, ground-based laser in the 100 GW range will concentrate its energy on the fleet of light sail enabled nanocraft for 10 minutes, accelerating them to 20% light speed within a distance of 2 million Km or 5 times the distance to the moon.

There are many technical hurdles that have to be overcome, a big one being energy storage and communication. With miniaturization technology making leaps and strides, the project is within reach within a generation according to Yuri Milner and the project design team. As a proof of concept and to test the technology, a smaller-scale project to launch a fleet of nano-craft to Mars has been proposed.

For more information, to get involved or to contribute (yes, this project is open to the public), please visit the Breakthrough Starshot page at the Breakthrough Initiatives home page. In addition to the list of challenges set forth my Yuri Milner, there are many additional sources of information available with one notable example at NPR.

As the famous English poet John Masefield once said, repeated so eloquently and in perfect context by Captain Jean-Luc Picard of the Starship Enterprise

“And all I ask is a tall ship and a star to steer her by!”

Imagination is more important than knowledge”, Albert Einstein

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