- 2978 - SPACE TRAVEL - is it practical? - For 9 billion years, multiple civilizations could have come and gone and while no one species could have colonized the entire galaxy, it’s hard to imagine that this activity would have gone unnoticed. Why haven’t we heard from any extraterrestrials?
---------------- 2978 - SPACE TRAVEL - is it practical?
- In 1950, Italian-American physicist Enrico Fermi introduced the question, “Where is everybody?“ This became the basis of the “Fermi Paradox“, which refers to the disparity between high probability estimates for the existence of extraterrestrial intelligence and the apparent lack of evidence.
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- Since Fermi’s time, there have been several proposed resolutions to his question, which includes the very real possibility that “interstellar colonization” follows the basic rule of “Percolation Theory“.
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- One of the key assumptions behind the Fermi Paradox is that given the abundance of planets and the age of the Universe, an advanced exo-civilization should have colonized a significant portion of our galaxy by now, considering that within the Milky Way galaxy alone, which is over 13,500,000,000 years old, there are an estimated 100 to 400 billion stars, and most all have planets.
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- Another key assumption is that intelligent species will be motivated to colonize other star systems as part of some natural drive to explore and extend the reach of their civilization. It also assumes that interstellar space travel would be feasible and even practical for an advanced exo-civilization.
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- The single greatest challenge of interstellar travel considering that the amount of energy it would take for a spacecraft to travel from one star to another is prohibitively large, especially where large, crewed spacecraft would be concerned.
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- In 1905, Einstein published his “Special Theory of Relativity“. This was Einstein’s attempt to reconcile “Newton’s Laws of Motion” with Maxwell’s “Equations of electromagnetism” in order to explain the behavior of light. This theory essentially states that the speed of light in addition to being constant is an absolute limit beyond which objects cannot travel.
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- This theory is summarized by the equation, E = mc2, which is also known as the “mass-energy equivalence.” This formula describes the energy (E) of a particle in its rest frame as the product of mass (m) with the speed of light squared (c^2), approximately 300,000 kilometers / second ; or, 186,000 miles / second. A consequence of this is that as an object approaches the speed of light, its mass invariably increases.
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- For an object to reach the speed of light, an infinite amount of energy would have to be expended accelerating it. Once “c” was achieved, the mass of the object would also become infinite. In short, achieving the speed of light is impossible, never mind exceeding it. So barring some tremendous revolution in our understanding of physics, a faster-than-light propulsion system can never exist.
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- Traveling at even a fraction of the speed of light requires tremendous amounts of energy. This raises a very important philosophical question that is related to the Fermi Paradox and the existence of extraterrestrials. This is the “Copernican Principle“, named in honor of famed astronomer Nicolaus Copernicus. This principle is an extension of Copernicus’ argument about the Earth, how it was not in a unique and privileged position to view the Universe.
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- The principle basically asserts that when considering the possibility of intelligent life, one should not assume that Earth, or humanity, is unique. Similarly, this principle holds that the Universe as we see it today is representative of the norm in a state of equilibrium.
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- The opposing view, that humanity is in a unique and privileged position to observe the Universe, is what is known as the “Anthropic Principle“. This principle states that the very act of observing the Universe for signs of life and intelligence requires that the laws that govern it be conducive to life and intelligence.
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- If we accept the “Copernican Principle” as a guiding principle, we are forced to concede that any intelligent species would face the same challenges with interstellar flight as we do. And since we do not foresee a way around these, barring major a breakthrough in our understanding of physics, perhaps no other species has found one either. Could this be the reason for the “Great Silence”?
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- By the time it would take for an extraterrestrials to have explored the entire galaxy is equal to or less than the age of our galaxy, 13.5 billion years . If an exo-civilization’s probes or signals have not reached us yet, this would imply that sentient life started to emerge in the more recent past. In other words, the galaxy is in a state of disequilibrium, moving from a state of being uninhabited to inhabited.
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- In a galaxy where intelligent life is statistically likely, there will not be a “uniformity of motive” among extraterrestrial civilizations. Since it is possible, given a large enough number of extraterrestrial civilizations, one or more would have certainly undertaken to do so, possibly for motives unknowable to us. Colonization will take an extremely longtime, and will be very expensive.
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- An advanced species would not colonize the galaxy rapidly or consistently. Instead, it would “percolate” outwards to a finite distance, where increasing costs and the lag time between communications imposed limits and colonies evolved their own cultures. Thus, colonization wouldn’t be uniform but would happen in clusters with large areas remaining uncolonized at any given time.
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- The settlement of the galaxy would occur in clusters because not all potentially habitable planets would be hospitable for a colonizing species. It would take between 1,000 and 81,000 years to reach Proxima Centauri (4.24 light-years away) using current technology.
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- While there are concepts that would allow for relativistic travel at a fraction of the speed of light, the travel time would still be anywhere from a few decades to over a century. What’s more, the cost would be extremely prohibitive.
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- To put interplanetary space travel in perspective, consider the costs associated with humanity’s own history of space exploration. Sending astronauts to the Moon as part of the Apollo Program between 1961 and 1973 cost a hefty $25,400,000,000, which works out to about $150 billion USD today, when adjusted for inflation.
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- But Apollo did not occur in a vacuum, and first required Project Mercury and Project Gemini as stepping stones. These two programs, which put the first American astronauts in orbit and developed the necessary expertise for getting to the Moon, respectively ran about $2,300,000,000 and $10 billion USD,when adjusted.
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- Add them all up, and you get a grand total of around $163 billion spent from 1958 to 1972. By comparison, Project Artemis, which will return astronauts to the Moon for the first time since 1972, will cost $35 billion over just the next four years!
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- That doesn’t include the costs of getting all the various components, the Orion space capsule, and research into the Lunar Gateway, human landing systems, and robotic missions. That is a lot of money just to get to Earth’s only satellite. But that’s nothing compared to the costs of interstellar missions!
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- Since the dawn of the “Space Age“, many theoretical proposals have been made for sending spacecraft to the nearest stars. At the heart of each and every one these proposals was the same concern: can we reach the nearest stars in our lifetimes?
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- In order to meet this challenge, scientists contemplated a number of advanced propulsion strategies that would be capable of pushing spacecraft to relativistic speeds.
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- Of these, the most straightforward was definitely Project Orion (1958 to 1963), which would rely on a method known as Nuclear Pulse Propulsion. This project envisioned a massive starship that would use the explosive force generated by nuclear warheads to generate thrust.
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- These warheads would be released behind the spacecraft and detonated, creating nuclear pulses. These would be absorbed by a rear-mounted pressure plate, or “pusher”, that translate the explosive force into forward momentum. Though inelegant, the system was brutally simple and effective, and could theoretically achieve speeds of up to 5% the speed of light (54,000,000 kilometers / hour, or 5% of “c“).
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- According to estimates in 1968, an Orion spacecraft would weight between 400,000 and 4,000,000 metric tons. Dyson’s most conservative estimates also placed the cost of building such a craft at $367 billion ($2.75 trillion when adjusted for inflation). That’s about 78% of the US government’s annual revenue for 2019, and 10% of the country’s GDP.
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- Another idea was to build rockets that rely on thermonuclear reactions to generate thrust. Project Daedalus design called for a two-stage spacecraft that would generate thrust by fusing pellets of a deuterium/helium-3 in a reaction chamber using electron lasers.
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- This would create a high-energy plasma that would then be converted to thrust by a magnetic nozzle. The first stage of the spacecraft would operate for just over 2 years and accelerate the spacecraft to 7.1% the speed of light. This stage would then be jettisoned and the second stage would take over and accelerate the spacecraft up to about 12% of light speed over the course of 1.8 years.
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- The second-stage engine would then be shut down and the ship would enter into a 46-year cruise period. According to the Project’s estimates, the mission would take 50 years to reach Barnard’s Star 6 light-years away.
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- A fully-fueled Daedalus would weight as much as 60,000 metric tons and cost over $5,267 billion (based on 2012 estimates).
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- Adjust to 2020 USD, the price tag for a fully-assembled Daedalus would cost close to $6 trillion.
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- “Antimatter Propulsion” would rely on the annihilation of matter and antimatter (hydrogen and anti-hydrogen particles). This reaction unleashed as much energy as a thermonuclear detonation, as well as a shower of subatomic particles (pions and muons). These particles, which would then travel at one-third the speed of light, are channeled by a magnetic nozzle to generate thrust.
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- The cost of producing even a single gram of antimatter fuel is estimated to be around one trillion dollars. A two-stage antimatter rocket would need over 815,000 metric tons of fuel to make the journey to Proxima Centauri in approximately 40 years.
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- A spacecraft weighing 400 metric tons and 170 metric tons of antimatter fuel could reach 50% the speed of light. At this rate, the craft could reach Proxima Centauri in a little over 8 years.
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- In all cases, propellant makes up a large fraction of these concept’s overall mass. To address this, variations have been proposed that could generate their own propellant. In the case of fusion rockets, there’s the “Bussard Ramjet“, which uses an enormous electromagnetic funnel to “scoop” hydrogen from the interstellar medium and magnetic fields to compress it to the point that fusion occurs.
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- “The Vacuum to Antimatter Rocket Interstellar Explorer System” (VARIES) creates its own fuel out of the interstellar medium. A VARIES ship would rely on large lasers (powered by enormous solar arrays) that would create particles of antimatter when fired at empty space.
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- Any idea for interstellar crewed missions is simply impractical, but sending probes to other stars within our lifetimes is still within the realm of possibility. As proposals like Breakthrough “Starshot” or Project “Dragonfly” show, these sails could be accelerated to relativistic speeds and have all the necessary hardware to gather pictures and basic data on any orbiting exoplanets.
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- Project “Starshot” is intended to be humanity’s first interstellar voyage. However, such probes are a potentially-reliable and cost-effective means of interstellar exploration, not colonization. The time-lag involved in interstellar communications would still place constraints on how far these probes could explore while still reporting back to Earth.
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- A possible criticism of percolation theory is that it allows for many scenarios and interpretations that would permit contact to have happened at this point. If we assume that an intelligent species would similarly take 4.5 billion years to emerge, the time between Earth’s formation and modern humans, and consider that our galaxy has been around for 13.5 billion years, that still leaves a 9 billion years window.
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- For 9 billion years, multiple civilizations could have come and gone and while no one species could have colonized the entire galaxy, it’s hard to imagine that this activity would have gone unnoticed.
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- Why haven’t we heard from any extraterrestrials? Because it’s unrealistic to conclude that they should have colonized the better part of the galaxy by now, especially when the laws of physics preclude such a thing.
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- Being stuck here on Earth you would think we would find better ways to get along.
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January 13, 2021 SPACE TRAVEL - is it practical? 2978
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