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The Fermi Paradox poses an age-old question: With light and radio waves skipping across the galaxy, why has there never been any convincing evidence of other life in the universe—or at least another sufficiently advanced civilization that uses radio? After all, evidence of intelligent life requires only that some species modulates a beacon (intentionally or unintentionally) in a fashion that is unlikely to be caused by natural phenomena.

The Fermi Paradox has always fascinated me, perhaps because SETI spokesperson, Carl Sagan was my astronomy professor at Cornell and—coincidentally—Sagan and Stephen Spielberg dedicated a SETI radio telescope at Oak Ridge Observatory around the time that I moved from Ithaca to New England. It’s a 5 minute drive from my new home. In effect, two public personalities followed me to Massachusetts.

What is SETI?

In November of 1984, SETI was chartered as a non-profit corporation with a single goal. In seeking to answer to the question “Are we alone?” it fuels the Drake equation by persuading radio telescopes to devote time to the search for extraterrestrial life and establishing an organized and systematic approach to partitioning, prioritizing, gathering and mining signal data.

Sagan explains the Drake Equation

Many of us associate astronomer Carl Sagan and Hollywood director, Stephen Spielberg, with SETI. They greased the path with high-profile PR that attracted interest, funding and radio-telescope partnerships. But, they were neither founders nor among the early staff. The founders, John Billingham and Barney Oliver assembled a powerhouse board of trustees, which included Frank Drake (Sagan’s boss at Cornell), Andrew Fraknol, Roger Heyns and William Welch. Among first hires were Jill Tarter, Charles Seeger, Ivan Linscott, Tom Pierson and Elyse Murray (now Elyse Pierson). Of course, Carl Sagan was advocated for the search for extraterrestrial intelligence, and he joined SETI as Trustee near the end of his life.

In The Birth of SETI, Tom Pierson reminisces about the early days of SETI. Also check out SETI pioneer, Jill Tarter, explaining how to write a message that will be understood by an alien civilization.

There is a lot of lore and love surrounding SETI, because its goal pulls directly on our need to understand our place in the cosmos. This week, SETI is going through a bit of transformation as it prepares for the next chapter in the search. So, where are the aliens? Are the funds and brainpower spent on peeping for aliens an investment in our own civilization, a form of entertainment, or a colossal waste?

This fascinating video offers 10 plausible solutions to Fermi Paradox. Fascinating, that is, if you can get past John Michael Godier’s dry, monotone narration. But. take my word for it. The concept and the content is exciting.

What’s wrong with this illustration of the planets in our solar system? »

For one thing, it suggests that the planets line up for photos on the same solar ray, just like baby ducks in a row. That’s a pretty rare occurrence—perhaps once in several billion years. In fact, Pluto doesn’t even orbit on the same plane as the planets. Its orbit is tilted 17 degrees. So, forget it lining up with anything, except on rare occasions, when it crosses the equatorial plane. On that day, you might get it to line up with one or two planets.

But what about scale? Space is so vast. Perhaps our solar system looks like this ↓

No such luck! Stars and planets do not fill a significant volume of the void. They are lonely specs in the great enveloping cosmic dark.* Space is mostly filled with—well—space! Lots and lots of it. In fact, if Pluto and our own moon were represented by just a single pixel on your computer screen, you wouldn’t see anything around it. Even if you daisy chain a few hundred computer screens, you will not discern the outer planets. They are just too far away.

Josh Worth has created an interactive map of our solar system. For convenience, it also assumes that planets are lined up like ducks. But the relative sizes and distance between planets are accurate. Prepare to change your view of the cosmos…

1/7 the way to Pluto. I enlarged Jupiter’s moons. On a full-screen view, they are barely visible.

Just swipe your finger from the right edge of the screen to move away from the sun. Despite a fascinating experience (and many cute, provocative Easter eggs hidden between the planets), few readers swipe all the way out to Pluto and the author credits. On my high-resolution monitor, it requires more than a thousand swipes. Imagine if the Moon had been more than 1 pixel…It would take a long, long time! I would rather go out to dinner and a movie. But I urge you to travel at least to Jupiter. At 1/7 of the trip to Pluto, it should take less than 5 minutes.

On this scale, you won’t see the 1½ or 2 million asteroids between Mars and Jupiter. They aren’t large enough to merit a pixel. As Josh states, “Most space charts leave out the most significant part – all the space.” (an Easter egg at 1.12 billion km on the map).

* I borrowed this phrase from my former Cornell professor, Carl Sagan. He uses it in Pale Blue Dot [timestamp 2:14.]. This video tribute became a touchstone in my life; even more than having Sagan as a professor and mentor.

If you view it, be sure to also view Consider Again, Sagan’s follow-up in the video below. It is a thought-provoking observation of human-chauvinism throughout history—even among ancient Greeks. Carl isn’t the first atheist, of course. But he is eloquent in describing mankind’s ego trip: The delusion of a privileged place in the universe, or the religious depiction of God and his relationship with our species.


Credit: ▪ Josh Worth and Sachin Gadhave who offers an illustrative answer at

Philip Raymond co-chairs Crypsa & Bitcoin Event, columnist & board member at Lifeboat, editor
at WildDuck and will deliver the keynote address at Digital Currency Summit in Johannesburg.

I am not an astronomer or astrophysicist. I have never worked for NASA or JPL. But, during my graduate year at Cornell University, I was short on cross-discipline credits, and so I signed up for Carl Sagan’s popular introductory course, Astronomy 101. I was also an amateur photographer, occasionally freelancing for local media—and so the photos shown here, are my own.

Carl Sagan is aware of my camera as he talks to a student in the front row of Uris Hall

By the end of the 70’s, Sagan’s star was high and continuing to rise. He was a staple on the Tonight Show with Johnny Carson, producer and host of the PBS TV series, Cosmos, and he had just written Dragons of Eden, which won him a Pulitzer Prize. He also wrote Contact, which became a blockbuster movie, starring Jodie Foster.

Sagan died in 1996, after three bone marrow transplants to compensate for an inability to produce blood cells. Two years earlier, Sagan wrote a book and narrated a film based on a photo taken from space.PaleBlueDot-1

Pale Blue Dot is a photograph of Earth taken in February 1990, by Voyager 1 from a distance of 3.7 billion miles (40 times the distance between earth and the sun). At Sagan’s request (and with some risk to the ongoing scientific mission), the space probe was turned around to take this last photo of Earth. In the photo, Earth is less than a pixel in size. Just a tiny dot against the vastness of space, it appears to be suspended in bands of sunlight scattered by the camera lens.

Four years later, Sagan wrote a book and narrated the short film, Pale Blue Dot, based on the landmark 1990 photograph. He makes a compelling case for reconciliation between humans and a commitment to care for our shared environment. In just 3½ minutes, he unites humanity, appealing to everyone with a conscience. [Full text]

—Which brings us to a question: How are we doing? Are we getting along now? Are we treating the planet as a shared life-support system, rather than a dumping ground?

Sagan points out that hate and misunderstanding plays into so many human interactions. He points to a deteriorating environment and that that we cannot escape war and pollution by resettling to another place. Most importantly, he forces us to face the the fragility of our habitat and the need to protect it. He drives home this point by not just explaining it, but by framing it as an urgent choice between life and death.

It has been 22 years since Sagan wrote and produced Pale Blue Dot. What has changed? Change is all around us, and yet not much has changed. To sort it all out, let’s break it down into technology, our survivable timeline and sociology.

Technology & Cosmology

  • Since Carl Sagan’s death, we have witnessed the first direct evidence of exoplanets. Several hundred have been observed and we will likely find many hundreds more each year. Some of these are in the habitable zone of their star.
  • Sagan died about 25 years after the last Apollo Moon mission. It is now 45 years since those missions, and humans are still locked into low earth orbits. We have sent a few probes to the distant planets and beyond, but the political will and resources to conduct planetary exploration—or even return to the moon—is weak.
  • A few private companies are launching humans, satellites or cargo into Space (Space-X, Virgin Galactic, Blue Origin). Dozens of other private ventures have not yet achieved manned flight or an orbital rendezvous, but it seems likey that some projects will succeed. Lift off is becoming commonplace—but almost all of these launches are focused on TV, communications, monitoring our environment or monitoring our enemies. The space program no longer produces the regular breakthroughs and commercial spin-offs that it did throughout the 70s and 80s.
    continue below photo…
Sagan explains the Drake Equation. (Click for 2 photos with solution)
Sagan explains the Drake Equation. (Click for 2 photos with solution)

Survivable Timeline

  • Like most scientists, Carl Sagan was deeply concerned about pollution, nuclear proliferation, loss of bio-diversity, war and global warming. In fact, the debate over global warming was just beginning to heat up in Sagan’s last years. Today, there is no debate over global warming. All credible scientists understand that the earth is choking, and that our activities are contributing to our own demise.
  • In most regions, air pollution is slightly less of a concern than it was in the 1970s, but ground, water pollution, and radiation contamination are all more evident.
  • Most alarmingly, we humans are even more pitched in posturing and in killing our neighbors than ever before. We fight over land, religion, water, oil, and human rights. We especially fight in the name of our Gods, in the name of national exceptionalism and in the name of protecting our right to consume disposable luxury gadgets, transient thrills and family vacations—as if we were a prisoner consuming his last meal.

We have an insatiable appetite for raw materials, open spaces, cars and luxury. Yet no one seems to be doing the math. As the vast populations of China and India finally come to the dinner table (2 billion humans), it is clear that they have the wealth to match our gluttony. From where will the land, water, and materials come? And what happens to the environment then? In Beijing, the sky is never blue. Every TV screen is covered in a thick film of dust. On many days, commuters wear filter masks. There is no grass in the parks and no birds in the sky. Something is very wrong. With apologies for a mixed metaphor, the canary is already dead while the jester continues to dance.

Carl Sagan's wife designed the plaque bolted to the outside of the first man made object to leave our solar system
This plaque is bolted onto the first man-made object to leave our solar system

Sociology: Man’s Inhumanity to Man

  • Sagan observed that our leaders are passionate about conquering each other, spilling blood over frequent misunderstandings, giving in to imagined self-importance. None of this has changed.
  • Regarding our ability to get off of this planet, Sagan said “Visit? Perhaps…Settle? Not yet”. We still do not possess the technology or resources to settle even a single astronaut away from our fragile home planet. We won’t have both the technology and the will to do so for at least 75 years—and then, only a tiny community of scientists or explorers. It falls centuries shy of resettling a population.
  • Hate, zealotry, intolerance and religious fervor are more toxic than ever before
  • Today, the earth has a bigger population. Hate and misunderstanding has spread like cancer. Weapons of mass destruction have escaped the restraint of governments, oversight and safety mechanisms. They are now in the hands of intolerant and radical organizations that believe in martyrdom and that lack any desire to coexist within a global community.


  • Nations, organizations and some individuals possess the technology to kill a million people or more. Without even targeting civilians, a dozen nations can lay waste to the global environment in weeks.

Is it time to revisit Pale Blue Dot? Is it still relevant? The urgency of teaching and heeding Carl Sagan’s words has never been more urgent than now.


Carl Sagan probably didn’t like me. When I was his student, I was a jerk.

Sagan was already a TV personality and author when I took Astronomy 101 in 1977. Occasionally, he discussed material from the pages of his just-released Dragons of Eden, or slipped a photo of himself with Johnny Carson into a slide presentation. He clearly was a star attraction during parent’s weekend before classes started.

Indeed, he often used the phrase “Billions and Billions” even before it led as his trademark. Although he seemed mildly mused that people noticed his annunciation and emphasis, he explained that he thought it was a less distracting alternate to the phrase “That’s billions with a ‘B’ ” when generating appreciation for the vast scope of creation.

At this time that Sagan was my professor, he appeared on the cover of Newsweek magazine. Like a lunkhead, I wrote to Newsweek, claiming that his adulation as a scientist was misplaced and that he was nothing more than an PR huckster for NASA and JPL in the vein of Isaac Asimov. I acknowledged his a gift for popularizing science, but argued that he didn’t have the brains to contribute in any tangible way.

I was wrong, of course. Even in the role of education champion, I failed to appreciate the very powerful and important role that he played in influencing an entire generation of scientists, including, Neil DeGrasse Tyson. Although Newsweek did not publish my letter to the editor, someone on staff sent it to Professor Sagan! When the teaching assistant, a close friend of Sagan, showed me my letter, I was mortified.

Incidentally, I always sat in the front row of the big Uris lecture hall. As a student photographer, I took many photos, which show up on various university web sites from time to time. In the top photo, Professor Sagan is crouching down and clasping hands as he addresses the student seated next to me.

The 100,000 Stars Google Chrome Galactic Visualization Experiment Thingy

So, Google has these things called Chrome Experiments, and they like, you know, do that. 100,000 Stars, their latest, simulates our immediate galactic zip code and provides detailed information on many of the massive nuclear fireballs nearby.

Zoom in & out of interactive galaxy, state, city, neighborhood, so to speak.

It’s humbling, beautiful, and awesome. Now, is 100, 000 Stars perfectly accurate and practical for anything other than having something pretty to look at and explore and educate and remind us of the enormity of our quaint little galaxy among the likely 170 billion others? Well, no — not really. But if you really feel the need to evaluate it that way, you are a unimaginative jerk and your life is without joy and awe and hope and wonder and you probably have irritable bowel syndrome. Deservedly.

The New Innovation Paradigm Kinda Revisited
Just about exactly one year ago technosnark cudgel was rapping about the changing innovation paradigm in large-scale technological development. There’s chastisement for Neil deGrasse Tyson and others who, paraphrasically (totally a word), have declared that private companies won’t take big risks, won’t do bold stuff, won’t push the boundaries of scientific exploration because of bottom lines and restrictive boards and such. But new business entities like Google, SpaceX, Virgin Galactic, & Planetary Resources are kind of steadily proving this wrong.

Google in particular, a company whose U.S. ad revenue now eclipses all other ad-based business combined, does a load of search-unrelated, interesting little and not so little research. Their mad scientists have churned out innovative, if sometimes impractical projects like Wave, Lively, and Sketchup. There’s the mysterious Project X, rumored to be filled with robots and space elevators and probably endless lollipops as well. There’s Project Glass, the self-driving cars, and they have also just launched Ingress, a global augmented reality game.

In contemporary America, this is what cutting-edge, massively well-funded pure science is beginning to look like, and it’s commendable. So, in lieu of an national flag, would we be okay with a SpaceX visitor center on the moon? Come on, really — a flag is just a logo anyway!

Let’s hope Google keeps not being evil.


(this post originally published at

The Kline Directive: Theoretical-Empirical Relationship (Part 4)

Posted in business, cosmology, defense, economics, education, engineering, nuclear weapons, particle physics, philosophy, physics, policy, scientific freedom, spaceTagged , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , | 11 Comments on The Kline Directive: Theoretical-Empirical Relationship (Part 4)

To achieve interstellar travel, the Kline Directive instructs us to be bold, to explore what others have not, to seek what others will not, to change what others dare not. To extend the boundaries of our knowledge, to advocate new methods, techniques and research, to sponsor change not status quo, on 5 fronts, Legal Standing, Safety Awareness, Economic Viability, Theoretical-Empirical Relationship, & Technological Feasibility.

In this post I have updated the Interstellar Challenge Matrix (ICM) to guide us through the issues so that we can arrive at interstellar travel sooner, rather than later:

Interstellar Challenge Matrix (Partial Matrix)

Propulsion Mechanism Relatively Safe? Theoretical-Empirical Relationship?
Conventional Fuel Rockets: Yes, but susceptible to human error. Known. Theoretical foundations are based on Engineering Feasible Theories, and have been evolving since Robert Goddard invented the first liquid-fueled rocket in 1926.
Antimatter Propulsion: No. Extensive gamma ray production (Carl Sagan). Issue is how does one protect the Earth? Capable of an End of Humanity (EOH) event. Dependent on Millennium Theories. John Eades states in no uncertain terms that antimatter is impossible to handle and create.
Atomic Bomb Pulse Detonation: No, because (Project Orion) one needs to be able to manage between 300,000 and 30,000,000 atomic bombs per trip. Known and based on Engineering Feasible Theories.
Time Travel: Do Not Know. Depends on how safely exotic matter can be contained. Dependent on a Millennium Theory. Exotic matter hypotheses are untested. No experimental evidence to show that Nature allows for a breakdown in causality.
String / Quantum Foam Based Propulsion: Do Not Know. Depends on how safely exotic matter can be contained. Dependent on a Millennium Theory. String theories have not been experimentally verified. Exotic matter hypotheses are untested. Existence of Quantum Foam now suspect (Robert Nemiroff).
Small Black Hole Propulsion: No. Capable of an End Of Humanity (EOH) event Don’t know if small black holes really do exist in Nature. Their theoretical basis should be considered a Millennium Theory.

It is quite obvious that the major impediments to interstellar travel are the Millennium Theories. Let us review. Richard Feynman (Nobel Prize 1965) & Sheldon Lee Glashow (Nobel Prize 1979) have criticized string theory for not providing novel experimental predictions at accessible energy scales, but other theoretical physicists (Stephen Hawking, Edward Witten, Juan Maldacena and Leonard Susskind) believe that string theory is a step towards the correct fundamental description of nature. The Wikipedia article String Theory gives a good overview, and notes other critics and criticisms of string theories. In What is String Theory? Alberto Güijosa explains why string theories have come to dominate theoretical physics. It is about forces, and especially about unifying gravity with the other three forces.

Note, strings expand when their energy increases but the experimental evidence aka Lorentz-Fitzgerald transformations tell us that everything contracts with velocity i.e. as energy is increased.

In my opinion, the heady rush to a theory of everything is misguided, because there is at least one question that physics has not answered that is more fundamental than strings and particles. What is probability and how is it implemented in Nature?

Probabilities are more fundamental than particles as particles exhibit non-linear spatial probabilistic behavior. So how can one build a theory of everything on a complex structure (particles), if it cannot explain something substantially more fundamental (probabilities) than this complex structure? The logic defies me.

We can ask more fundamental questions. Is this probability really a Gaussian function? Experimental data suggests otherwise, a Var-Gamma distribution. Why is the force experienced by an electron moving in a magnetic field, orthogonal to both the electron velocity and the magnetic field? Contemporary electromagnetism just says it is vector cross product, i.e. it is just that way. The cross product is a variation of saying it has to be a Left Hand Rule or a Right Hand Rule. But why?

Is mass really the source of a gravitational field? Could it not be due to quark interaction? Can we device experiments that can distinguish between the two? Why do photons exhibit both wave and particle behavior? What is momentum, and why is it conserved? Why is mass and energy equivalent?

Can theoretical physicists construct theories without using the laws of conservation of mass-energy and momentum? That would be a real test for a theory of everything!

In my research into gravity modification I found that the massless formula for gravitational acceleration, g=τc2, works for gravity, electromagnetism and mechanical forces. Yes, a unification of gravity and electromagnetism. And this formula has been tested and verified with experimental data. Further that a force field is a Non Inertia (Ni) field, and is present where ever there is a spatial gradient in time dilations or velocities. This is very different from the Standard Model which requires that forces are transmitted by the exchange of virtual particles.

So if there is an alternative model that has united gravity and electromagnetism, what does that say for both string theories and the Standard Model? I raise these questions because they are opportunities to kick start research in a different direction. I answered two of these questions in my book. In the spirit of the Kline Directive can we use these questions to explore what others have not, to seek what others will not, to change what others dare not?

That is why I’m confident that we will have real working gravity modification technologies by 2020.

In concluding this section we need to figure out funding rules to ensure that Engineering Feasible and 100-Year Theories get first priority. That is the only way we are going to be able to refocus our physics community to achieve interstellar travel sooner rather than later.

Previous post in the Kline Directive series.

Next post in the Kline Directive series.


Benjamin T Solomon is the author & principal investigator of the 12-year study into the theoretical & technological feasibility of gravitation modification, titled An Introduction to Gravity Modification, to achieve interstellar travel in our lifetimes. For more information visit iSETI LLC, Interstellar Space Exploration Technology Initiative.

Solomon is inviting all serious participants to his LinkedIn Group Interstellar Travel & Gravity Modification.

To achieve interstellar travel, the Kline Directive instructs us to be bold, to explore what others have not, to seek what others will not, to change what others dare not. To extend the boundaries of our knowledge, to advocate new methods, techniques and research, to sponsor change not status quo, on 5 fronts:

1. Legal Standing. 2. Safety Awareness. 3. Economic Viability. 4. Theoretical-Empirical Relationship. 5. Technological Feasibility.

In this post I will explore Safety Awareness.

In the heady rush to propose academically acceptable ideas about new propulsions systems or star drives it is very easy to overlook safety considerations. The eminent cosmologist Carl Sagan said it best “So the problem is not to shield the payload, the problem is to shield the earth” (Planet. Space Sci., pp. 485 – 498, 1963)

It is perfectly acceptable if not warranted to propose these technologically infeasible star drives based on antimatter and exotic matter, as academic exercises because we need to understand what is possible and why. However, we need to inform the public of the safety issues when doing so.

I do not understand how any physicist or propulsion engineer, in his/her right mind, not qualify their academic exercise in antimatter propulsion or star drive with a statement similar to Carl Saga’s. At the very least it gets someone else thinking about those safety problems, and we can arrive at a solution sooner, if one exists.

We note that the distinguished Carl Sagan did not shy away from safety issues. He was mindful of the consequences and is an example of someone pushing the limits of safety awareness in the spirit of the Kline Directive, to explore issues which others would (could?) not.

We have to ask ourselves, how did we regress? From Sagan’s let us consider all ancillary issues, to our current let us ignore all ancillary issues. The inference I am forced to come to is that Carl Sagan was a one-man team, while the rest of us lesser beings need to come together as multi-person teams to stay on track, to achieve interstellar travel.

In interstellar & interplanetary space there are two parts to safety, radiation shielding and projectile shielding. Radiation shielding is about shielding from x-ray and gamma rays. Projectile shielding is about protection from physical damage caused by small particle collisions.

I may be wrong but I haven’t come across anyone even attempting to address either problems. I’ve heard of strategies such as using very strong electric fields or even of using millions of tons of metal shielding but these are not realistic. I’ve even heard of the need to address these issues but nothing more.

Safety is a big issue that has not been addressed. So how are we going to solve this? What do we need to explore that others have not? What do we need to seek that others would not? What do we need to change, that others dare not?

Previous post in the Kline Directive series.

Next post in the Kline Directive series.


Benjamin T Solomon is the author & principal investigator of the 12-year study into the theoretical & technological feasibility of gravitation modification, titled An Introduction to Gravity Modification, to achieve interstellar travel in our lifetimes. For more information visit iSETI LLC, Interstellar Space Exploration Technology Initiative.

Solomon is inviting all serious participants to his LinkedIn Group Interstellar Travel & Gravity Modification.

Previous Post in this Debunking Series.

Why is it necessary to debunk bad or unrealistic technologies? If don’t we live in a dream world idealized by theoretical engineering that has no hope of ever becoming financially feasible. What a waste of money, human resources and talent. I’d rather we know now upfront and channel our energies to finding feasible engineering and financial solutions. Wouldn’t you?

We did the math required to figure out the cost of antimatter fuel one would require just to reach 0.1c and then cost at that velocity, never mind about reaching Alpha Centauri.

Table 2: Antimatter Rocket Fuel Costs to Alpha Centuariat 0.1c (in metric tons)
Source of Estimates Amount of Antimatter Required Maximum Velocity

Spacecraft Mass

Cost of Antimatter per kg

(metric tons) (metric tons)

Gerald Smith




Total $ Cost of Fuel for Trip

A Poor Formula for Interstellar Travel






Project Valkyrie






The table above compiled from various sources shows that the cheapest cost of just reaching 0.1c velocity is of the order of $125,000,000,000,000,000,000. This so unthinkably large even I don’t know how to conceptualize it, and by comparison, conventional rockets appear realistic!

Also note that the large variations in the estimates of the amount of antimatter required combined with the larger variations in the mass of the spacecraft antimatter engines could propel. That is no one reallys has a handle on what this would take.

But wait, let me quote EJ Opik, “Is Interstellar Travel Possible?” Irish Astronomical Journal, Vol 6, page 299.

The exhaust power of the antimatter rocket would equal the solar energy power received by the earth — all in gamma rays (and Opik quotes Carl Sagan, Planet. Space Sci., pp. 485–498, 1963) “So the problem is not to shield the payload, the problem is to shield the earth

I don’t need to say more. Debunked.

Next psot in this Debunking Series.


Benjamin T Solomon is the author & principal investigator of the 12-year study into the theoretical & technological feasibility of gravitation modification, titled An Introduction to Gravity Modification, to achieve interstellar travel in our lifetimes. For more information visit iSETI LLC, Interstellar Space Exploration Technology Initiative.

Solomon is inviting all serious participants to his LinkedIn Group Interstellar Travel & Gravity Modification.