Manned flight to other stars is possible. Interstellar travel is much more real than you think. What conditions to fly under?

02.07.2020

Reviews of the book The True, Mad, Guilty Moriarty l The True, Mad, Guilty

Life at Full Power - Jim Lauer, Tony Schwartz

Famous pirates of the Caribbean, next to whom the movie Jack Sparrow is just a boy

Our reader Nikita Ageev asks: what is the main problem of interstellar travel? The answer, like , will require a long article, although the question can be answered with a single symbol: c .

The speed of light in a vacuum, c, is approximately three hundred thousand kilometers per second, and it is impossible to exceed it. Therefore, it is impossible to reach the stars faster than in a few years (light travels 4.243 years to Proxima Centauri, so the spacecraft cannot arrive even faster). If you add the time for acceleration and deceleration with acceleration more or less acceptable for humans, you get about ten years to the nearest star.

What are the conditions to fly under?

And this period is already a significant obstacle in itself, even if we ignore the question “how to accelerate to a speed close to the speed of light.” Now there are no spaceships that would allow the crew to live autonomously in space for so long - the astronauts are constantly brought fresh supplies from Earth. Usually, conversations about the problems of interstellar travel begin with more fundamental questions, but we will start with purely applied problems.

Water for washing, washing and drinking will also have to be either taken with you or reused. As well as air, and food also needs to be either stored or grown on board. Experiments to create a closed ecosystem on Earth have already been carried out, but their conditions were still very different from space ones, at least in the presence of gravity. Humanity knows how to turn the contents of a chamber pot into clean drinking water, but in this case it is necessary to be able to do this in zero gravity, with absolute reliability and without a truckload of consumables: taking a truckload of filter cartridges to the stars is too expensive.

Washing socks and protecting against intestinal infections may seem like too banal, “non-physical” restrictions on interstellar flights - however, any experienced traveler will confirm that “little things” like uncomfortable shoes or stomach upset from unfamiliar food on an autonomous expedition can turn into a threat to life.

Solving even basic everyday problems requires just as serious a technological base as the development of fundamentally new space engines. If on Earth a worn-out gasket in a toilet cistern can be bought at the nearest store for two rubles, then on the Martian ship it is necessary to provide either a reserve everyone similar parts, or a three-dimensional printer for the production of spare parts from universal plastic raw materials.

In the US Navy in 2013 in earnest started 3D printing after we assessed the time and money spent on repairing military equipment using traditional methods in the field. The military reasoned that printing some rare gasket for a helicopter component that had been discontinued ten years ago was easier than ordering a part from a warehouse on another continent.

One of Korolev’s closest associates, Boris Chertok, wrote in his memoirs “Rockets and People” that at a certain point the Soviet space program was faced with a shortage of plug contacts. Reliable connectors for multi-core cables had to be developed separately.

In addition to spare parts for equipment, food, water and air, astronauts will need energy. The engine and on-board equipment will need energy, so the problem of a powerful and reliable source will have to be solved separately. Solar batteries are not suitable, if only because of the distance from the stars in flight, radioisotope generators (they power Voyagers and New Horizons) do not provide the power required for a large manned spacecraft, and they have not yet learned how to make full-fledged nuclear reactors for space.

The Soviet nuclear-powered satellite program was marred by an international scandal following the crash of Cosmos 954 in Canada, as well as a series of failures with less dramatic consequences; similar work in the United States was stopped even earlier. Now Rosatom and Roscosmos intend to create a space nuclear power plant, but these are still installations for short-range flights, and not a multi-year journey to another star system.

Perhaps instead of a nuclear reactor, future interstellar spacecraft will use tokamaks. About how difficult it is to at least correctly determine the parameters of thermonuclear plasma, at MIPT this summer. By the way, the ITER project on Earth is progressing successfully: even those who entered the first year today have every chance to join the work on the first experimental thermonuclear reactor with a positive energy balance.

What to fly?

Conventional rocket engines are not suitable for accelerating and decelerating an interstellar ship. Those familiar with the mechanics course taught at MIPT in the first semester can independently calculate how much fuel a rocket will need to reach at least one hundred thousand kilometers per second. For those who are not yet familiar with the Tsiolkovsky equation, we will immediately announce the result - the mass of fuel tanks turns out to be significantly higher than the mass of the Solar system.

The fuel supply can be reduced by increasing the speed at which the engine emits the working fluid, gas, plasma or something else, up to a beam of elementary particles. Currently, plasma and ion engines are actively used for flights of automatic interplanetary stations within the Solar System or for correction of the orbit of geostationary satellites, but they have a number of other disadvantages. In particular, all such engines provide too little thrust; they cannot yet give the ship an acceleration of several meters per second squared.

MIPT Vice-Rector Oleg Gorshkov is one of the recognized experts in the field of plasma engines. SPD series engines are produced at the Fakel Design Bureau; these are serial products for orbit correction of communication satellites.

In the 1950s, an engine project was developed that would use the impulse of a nuclear explosion (the Orion project), but it was far from becoming a ready-made solution for interstellar flights. Even less developed is the design of an engine that uses the magnetohydrodynamic effect, that is, accelerates due to interaction with interstellar plasma. Theoretically, a spacecraft could “suck” plasma inside and throw it back out to create jet thrust, but this poses another problem.

How to survive?

Interstellar plasma is primarily protons and helium nuclei, if we consider heavy particles. When moving at speeds of the order of hundreds of thousands of kilometers per second, all these particles acquire energy of megaelectronvolts or even tens of megaelectronvolts - the same amount as the products of nuclear reactions. The density of the interstellar medium is about one hundred thousand ions per cubic meter, which means that per second a square meter of the ship's hull will receive about 10 13 protons with energies of tens of MeV.

One electronvolt, eV,― This is the energy that an electron acquires when flying from one electrode to another with a potential difference of one volt. Light quanta have this energy, and ultraviolet quanta with higher energy are already capable of damaging DNA molecules. Radiation or particles with energies of megaelectronvolts accompanies nuclear reactions and, in addition, is itself capable of causing them.

Such irradiation corresponds to an absorbed energy (assuming that all energy is absorbed by the skin) of tens of joules. Moreover, this energy will not just come in the form of heat, but may partially be used to initiate nuclear reactions in the ship’s material with the formation of short-lived isotopes: in other words, the lining will become radioactive.

Some of the incident protons and helium nuclei can be deflected aside by a magnetic field; induced radiation and secondary radiation can be protected by a complex shell of many layers, but these problems also have no solution yet. In addition, fundamental difficulties of the form “which material will be least destroyed when irradiated” at the stage of servicing the ship in flight will turn into particular problems - “how to unscrew four 25 bolts in a compartment with a background of fifty millisieverts per hour.”

Let us recall that during the last repair of the Hubble telescope, the astronauts initially failed to unscrew the four bolts that secured one of the cameras. After consulting with the Earth, they replaced the torque-limiting key with a regular one and applied brute force. The bolts moved out of place, the camera was successfully replaced. If the stuck bolt had been removed, the second expedition would have cost half a billion US dollars. Or it wouldn’t have happened at all.

Are there any workarounds?

In science fiction (often more fantasy than science), interstellar travel is accomplished through “subspace tunnels.” Formally, Einstein's equations, which describe the geometry of space-time depending on the mass and energy distributed in this space-time, do allow something similar - but the estimated energy costs are even more depressing than estimates of the amount of rocket fuel for a flight to Proxima Centauri. Not only do you need a lot of energy, but also the energy density must be negative.

The question of whether it is possible to create a stable, large and energetically possible “wormhole” is tied to fundamental questions about the structure of the Universe as a whole. One of the unresolved problems in physics is the absence of gravity in the so-called Standard Model, a theory that describes the behavior of elementary particles and three of the four fundamental physical interactions. The vast majority of physicists are quite skeptical that in the quantum theory of gravity there will be a place for interstellar “jumps through hyperspace”, but, strictly speaking, no one forbids trying to look for a workaround for flights to the stars.

Scientists say that humanity is taking small steps towards a future in which flights from one planetary system to another will finally become a reality. According to the latest expert estimates, such a future could come within one or two centuries if scientific progress does not mark time. At one time, only with the help of the ultra-powerful Kepler telescope, astronomers were able to discover 54 potentially habitable exoplanets. All these worlds far from us are located in the so-called habitable zone, at a certain distance from the central star, which allows water to be maintained on the planet in a liquid state.

At the same time, it is quite difficult to get an answer to the most important question – are we alone in the Universe? Because of the very large distances that separate the solar system and our closest neighbors. For example, one of the “promising” planets, Gliese 581g, is located at a distance of 20 light years, which is quite close by space standards, but still very far for conventional terrestrial technologies. The abundance of exoplanets within a radius of 100 light years or less from our home planet and the very great scientific and even civilizational interest that they represent for all of humanity force us to look at the hitherto fantastic idea of interstellar flights in a completely new way.

The main task that cosmologists and engineers face today is the creation of a fundamentally new engine that would allow earthlings to travel vast cosmic distances in a relatively short time. At the same time, there is certainly no talk of intergalactic flights yet. To begin with, humanity could explore our home galaxy - the Milky Way.

The Milky Way consists of a large number of stars around which planets orbit. The star closest to the Sun is called Alpha Centauri. This star is 4.3 light years or 40 trillion kilometers away from Earth. If we assume that a rocket with a conventional engine takes off from our planet today, then it will be able to cover this distance only in 40 thousand years! Of course, such a space mission looks completely absurd. Mark Millis, former head of NASA's Advanced Engine Technologies Project and founder of the Tau Zero Foundation, believes that humanity needs to take a long and methodical path to creating a new type of engine. Nowadays, there are already a huge number of theories about what this engine will be like, but we don’t know which theory will work. Therefore, Millis considers it pointless to focus on just one technology.

Today, scientists have concluded that future spaceships will be able to fly using fusion drive, solar sail, antimatter drive or space-time warp drive (or warp drive, which is well known to fans of the TV series Star Trek). The latest engine, in theory, should make it possible to fly faster than the speed of light, and therefore small-scale time travel.

At the same time, all of the listed technologies are only described; no one yet knows how to implement them in practice. For the same reason, it is not clear which technology holds the most promise for implementation. True, a number of solar sails have already managed to fly into space, but to carry out a manned mission of interstellar flights, a huge sail the size of the Arkhangelsk region will be required. The principle of operation of a solar sail is practically no different from a wind sail, only instead of air flows, it catches hyper-focused rays of light emitted by a powerful laser installation rotating around the Earth.

Mark Millis, in a press release from his Tau Zero foundation, says that the truth is somewhere in the middle between solar sails that are almost familiar to us and completely fantastic developments, like a warp engine. “It is necessary to make scientific discoveries and slowly but surely move towards the intended goal. The more people we can interest, the greater the volume of funding we will attract; it is funding that is currently sorely lacking,” says Millis. Mark Millis believes that funding for large projects needs to be collected bit by bit, without expecting someone to suddenly invest a fortune in the implementation of ambitious plans of scientists.

Today, all over the world, there are a lot of enthusiasts who believe and are confident that the future needs to be built now. Richard Obusie, President and Co-Founder of Icarus Interstellar, notes: “Interstellar travel is an international, multi-generational endeavor that requires enormous intellectual and financial investment. Already today, we must initiate the necessary programs so that in a hundred years humanity will be able to escape beyond the boundaries of our solar system.”

In August of this year, the Icarus Interstellar company is going to hold a scientific conference, Starship Congress, at which the world's leading experts in the field will discuss not only the possibilities, but also the consequences of interstellar flights. The organizers note that the conference will also include a practical part, which will examine both short-term and long-term prospects for human exploration of deep space.

It is worth noting that such space travel requires the expenditure of colossal amounts of energy, which humanity today does not even think about. At the same time, improper use of energy can cause irreparable harm to both the Earth and those planets on the surface of which a person wants to land. Despite all the unresolved problems and obstacles, both Obuzi and Millis believe that human civilization has every chance of leaving the confines of its “cradle.” The invaluable data on exoplanets, star systems and alien worlds that have been collected by the Herschel and Kepler space observatories will help scientists carefully plan their missions.

To date, the existence of about 850 exoplanets has been discovered and confirmed, many of which are super-Earths, that is, planets with a mass comparable to that of Earth. Experts believe that the day is not far when astronomers will be able to confirm the presence of an exoplanet that would be like two peas in a pod like our own. In this case, funding for projects to create new rocket engines would increase significantly. The extraction of minerals from asteroids should also play a role in space exploration, which now does not sound as unusual as interstellar flights. Humanity must learn to use the resources not only of the Earth, but of the entire solar system, experts believe.

Scientists and engineers from the American space agency NASA, as well as the US Defense Advanced Research Projects Agency - DARPA, have joined the problem of interstellar flights. They are ready to join forces as part of the implementation of the “100-year Starship” project, and this is not even a project, but a project of a project. The 100-year Starship is a spaceship that could perform interstellar flights. The task of the current stage of research is to create the “sum of technologies” that are necessary for interstellar travel to become a reality. In addition, a business model is being created that would attract investment into the project.

According to Pavel Eremenko, a spokesman for DARPA, this project will require “stable investments in financial and intellectual capital” from various sources. Eremenko also emphasized that the goal of the “100-year Starship” project is not only the development and subsequent construction of a starship. “We are working hard to inspire multi-generational interest in innovation and breakthrough technologies across multiple disciplines.”

DARPA experts hope that the results that will be obtained from working on this project can be used by the US Department of Defense in various fields, such as life support systems, energy, and computer technology.

Information sources:
-http://www.vesti.ru/doc.html?id=1100469
-http://rnd.cnews.ru/reviews/index_science.shtml?2011/10/11/459501
-http://www.nkj.ru/news/18905

The answer will require a long article, although it can be answered with a single character: c .

Speed of light in vacuum c , is equal to approximately three hundred thousand kilometers per second and cannot be exceeded. Therefore, it is impossible to reach the stars faster than in a few years (light travels 4.243 years to Proxima Centauri, so the spacecraft cannot arrive even faster). If you add the time for acceleration and deceleration with acceleration more or less acceptable for humans, you get about ten years to the nearest star.

What are the conditions to fly under?

And this period is already a significant obstacle in itself, even if we ignore the question “how to accelerate to a speed close to the speed of light.” Now there are no spaceships that allowed the crew to live autonomously in space for so long - the astronauts are constantly brought fresh supplies from Earth. Usually, conversations about the problems of interstellar travel begin with more fundamental questions, but we will start with purely applied problems.

Even half a century after Gagarin’s flight, engineers were unable to create a washing machine and a sufficiently practical shower for spacecraft, and toilets designed for weightlessness break down on the ISS with enviable regularity. A flight to at least Mars (22 light minutes instead of 4 light years) already poses a non-trivial task for plumbing designers: so for a trip to the stars it will be necessary to at least invent a space toilet with a twenty-year guarantee and the same washing machine.

Water for washing, washing and drinking will also have to be either taken with you or reused. As well as air, and food also needs to be either stored or grown on board. Experiments to create a closed ecosystem on Earth have already been carried out, but their conditions were still very different from space ones, at least in the presence of gravity. Humanity knows how to turn the contents of a chamber pot into clean drinking water, but in this case it is necessary to be able to do this in zero gravity, with absolute reliability and without a truckload of consumables: taking a truckload of filter cartridges to the stars is too expensive.

Solving even basic everyday problems requires just as serious a technological base as the development of fundamentally new space engines. If on Earth a worn-out gasket in a toilet tank can be bought at the nearest store for two rubles, then on the Martian ship it is necessary to provide either a supply of all such parts, or a three-dimensional printer for the production of spare parts from universal plastic raw materials.

The US Navy got serious about 3D printing in 2013 after assessing the time and cost involved in repairing military equipment using traditional methods in the field. The military reasoned that printing some rare gasket for a helicopter component that had been discontinued ten years ago was easier than ordering a part from a warehouse on another continent.

Perhaps instead of a nuclear reactor, future interstellar spacecraft will use tokamaks. This summer, MIPT gave a whole lecture to everyone about how difficult it is to even correctly determine the parameters of thermonuclear plasma. By the way, the ITER project on Earth is progressing successfully: even those who entered the first year today have every chance to join the work on the first experimental thermonuclear reactor with a positive energy balance.

What to fly?

How to survive?

One electron volt, eV, is the energy that an electron acquires when flying from one electrode to another with a potential difference of one volt. Light quanta have this energy, and ultraviolet quanta with higher energy are already capable of damaging DNA molecules. Radiation or particles with energies of megaelectronvolts accompanies nuclear reactions and, in addition, is itself capable of causing them.

Are there any workarounds?

And left the solar system; Now they are used to study interstellar space. At the beginning of the 21st century, there are no stations whose direct mission would be to fly to the nearest stars.

The distance to the nearest star (Proxima Centauri) is about 4,243 light years, that is, about 268 thousand times the distance from Earth to the Sun.

Interstellar expedition projects

Project "Orion"

Starship projects driven by the pressure of electromagnetic waves

In 1971, in a report by G. Marx at a symposium in Byurakan, it was proposed to use X-ray lasers for interstellar flights. The possibility of using this type of propulsion was later investigated by NASA. As a result, the following conclusion was made: “If the possibility of creating a laser operating in the X-ray wavelength range is found, then we can talk about the real development of an aircraft (accelerated by the beam of such a laser) that will be able to cover distances to the nearest stars much faster than all known currently rocket-powered systems. Calculations show that using the space system considered in this work, it is possible to reach the star Alpha Centauri... in about 10 years."

In 1985, R. Forward proposed the design of an interstellar probe accelerated by microwave energy. The project envisaged that the probe would reach the nearest stars in 21 years.

At the 36th International Astronomical Congress, a project for a laser starship was proposed, the movement of which is provided by the energy of optical lasers located in orbit around Mercury. According to calculations, the path of a starship of this design to the star Epsilon Eridani (10.8 light years) and back would take 51 years.

Annihilation engines

The main problems identified by scientists and engineers who analyzed the designs of annihilation rockets are obtaining the required amount of antimatter, storing it, and focusing the flow of particles in the desired direction. It is indicated that the current state of science and technology does not even theoretically allow the creation of such structures.

Ram engines powered by interstellar hydrogen

The main component of the mass of modern rockets is the mass of fuel required by the rocket for acceleration. If we can somehow use the environment surrounding the rocket as a working fluid and fuel, we can significantly reduce the mass of the rocket and thereby achieve high speeds.

Generation ships

Interstellar travel is also possible using starships that implement the concept of “generation ships” (for example, like O’Neil’s colonies). In such starships, a closed biosphere is created and maintained, capable of maintaining and reproducing itself for several thousand years. The flight occurs at low speed and takes a very long time, during which many generations of astronauts manage to change.

FTL propulsion

Notes

Sources

Kolesnikov Yu. V. You should build starships. M., 1990. 207 p. ISBN 5-08-000617-X.
http://www.gazeta.ru/science/2008/01/30_a_2613225.shtml?4 Lecture on interstellar flights, on acceleration of 100 km/sec near stars

Social phenomena

Finance and crisis

Elements and weather

Science and technology

Unusual phenomena

Nature monitoring

Author sections

Discovering the story

Extreme World

Info reference

File archive

Discussions

Services

Infofront

Information from NF OKO

RSS export

useful links

Important Topics

Is interstellar travel possible?

In the endless depths of space, many trillions of miles away, far beyond the outermost planets of the solar system, the stars shine. There are a huge variety of them: red, yellow, orange, blue, white. Astronomers are confident that at least some of these stars heat the planets orbiting them. But it is quite possible that in the future we will witness the discovery of first dozens, and then hundreds of earth-like planets, perhaps even with reserves of water or signs of life.

From afar, astronomers are trying to study these planets and determine their basic properties, but the only way to thoroughly study all the details is to launch a spacecraft. Before space stations traveled into space, we knew little about the planets of the solar system. Some believed that Venus had oceans and Mars had canals, and no one really knew anything about such distant worlds as Uranus and Neptune.

Problems and prospects

No matter how much we would like to fly closer to the stars and see the planets orbiting them close-up, many scientists are confident that such trips will never happen. The energy and costs required to travel to Alpha Centauri, the closest star system to us, are so great that even proponents of interstellar travel are forced to reckon with them.

Proponents of space travel often refer to things that they previously did not believe in, but now take for granted.

For example, many scientists in the early twentieth century argued that airplanes would never be able to fly across the Atlantic Ocean. On the other hand, those who do not believe in the possibility of interstellar flights, with no less passion, recall the hopes of the past, which did not materialize contrary to all expectations. For example, not so long ago many believed that in the 90s we would all fly to work in our personal helicopters.

Among professional astronomers there are many who believe, albeit without any reason, that intelligent life is a very widespread phenomenon in the Galaxy. However, until now, no extraterrestrial race has bothered to visit Earth - a fact that prompted physicist Enrico Fermi to ask his famous question in 1950: “Where are they?” To explain this apparent contradiction, called the Fermi Paradox, astronomers who admit the existence of other habitable worlds in the Universe suggest that due to the difficulty of organizing and the high cost of the expedition, no civilization dares to undertake such trips. Consequently, we - earthlings - will never cope with this task.

To date, people have already managed to launch interplanetary ships into space and use them to study all the planets of the solar system from Mercury to Neptune, and only Pluto remains behind the dark strip of the unknown.

In a sense, the first interstellar ships of mankind were four automatic stations - Pioneer 10, Pioneer 11, Voyager 1 and Voyager 2; It is they who are now leaving the solar system at high speed, heading towards the stars. The Pioneer can cover a distance 2.3 times greater in a year than the distance between the Earth and the Sun, and the faster Voyagers can travel 3.4 times. But the stars are so far away that even Voyager would take 80,000 years to reach Alpha Centauri, which is 4.3 light years from Earth. But, if we’re lucky, it won’t come to that: the spaceships of future centuries will most likely catch up and overtake the modern “slow-moving” ones, and return them to their home planet as exhibits in the space exploration museum.

Distant goal

The biggest challenges star travelers will face are the vast distances to the stars. Astronomers so often convert distances into light years that they often forget how big a light year actually is. A beam of light is so fast that it can circle the Earth 7.5 times in one second. Thus, the distance traveled in a year will be truly great. Imagine that the Galaxy shrank so that the Earth and the Sun were only an inch (2.5 cm) apart. Jupiter would then be located five inches from the Sun, and distant Neptune only 30 inches away. And even on this scale, a light year would remain equal to a full mile (1.6 km), and Alpha Centauri would move 4.3 miles away from Earth. And if the Milky Way Galaxy, so huge and vast, were to shrink to the size of a dime, then the entire observable Universe, from the Earth to the most distant quasars known to us, would become no more than two miles wide.

"Voyagers" move in space at a speed of only 0.005% of light, but in order to send a real spaceship to Alpha Centauri and get to its destination in at least fifty years, while the scientists who organized the expedition are still alive, it is necessary to speed up this ship up to at least 10% light speed. For comparison: if you go beyond the solar system at “only” 1% the speed of light, it will take 430 years to reach Alpha Centauri, and over such a long period of time the level of technology can rise so much that it will become possible to build faster spaceships. Let's imagine that Christopher Columbus was a long-liver and it would take him 500 years to cross the Atlantic Ocean. Every now and then he would have been overtaken by more advanced ships, and fast airplanes would have managed to make the journey from Europe to America long before he himself reached the treasured shores. And when he finally got there, the New World, completely new to him, Columbus, would already be quite “old” to anyone else.

However, achieving high speeds close to the speed of light is very difficult because it requires a lot of energy and money. For example, a ship weighing one ton would require as much energy as a large industrial power consumes in a month. True, on solar scales this is quite a bit: the Sun alone emits a million times more energy into space every second. Thus, the energy is there, people just have to learn how to use it.

Another obstacle critics point to is the cost of the expedition. Such a trip could cost more than a trillion dollars. However, what is unimaginably expensive today can become cheap centuries later. After all, the American colonists in 1776 would not have dared to organize a flight to the Moon, both due to the lack of technology and the need for astronomical sums, and their descendants less than two centuries later successfully landed a man on the Moon. And if we managed to do this using the technology of the sixties, then why don’t our followers launch a man into orbit around Alpha Centauri?

Undoubtedly, the first interstellar travelers will be machines, not people. Man only reached the Moon, while automatic space stations have already been beyond Neptune.

Machines, unlike people, do not need air, water, food and minimal amenities. In addition, computers and instruments of future decades will become smaller, lighter and more powerful, which will reduce the weight of the spacecraft.

Einstein's theory

If we were to travel to the stars, we would inevitably encounter difficulties predicted by Einstein's theory of special relativity, which deals with the effects of bodies moving at close to the speed of light. The speed of light is the best known relativistic barrier; It is precisely because of the extreme nature of this speed that earthlings will have to wait at least 4.3 years until the ship reaches Alpha Centauri, and then another 4.3 years until the ship with the information returns to Earth.

Special relativity also describes the effect of speed on mass and time. As the speed of a spacecraft increases, its mass also increases, which is bad because it becomes more and more difficult to accelerate it. However, for any passenger on board a ship, time moves much more slowly, which is good because it allows you to travel longer distances. These two relativistic effects, affecting mass and time, are small at low speeds and increase greatly as the ship's speed approaches the speed of light. At a speed equal to the speed of light, the mass of a body becomes infinite, which is why no material body can move so fast.

Scientists express the level of influence of relativistic effects by the Lorentz coefficient, named after the Dutch physicist Hendrik Lorentz. The Lorentz coefficient depends on speed: it is equal to unity at zero speed, increases as the latter increases, and becomes infinite at the speed of light. At 20% the speed of light, the Lorentz coefficient is only 1.02, which means that a spacecraft moving at that speed is only 2% heavier than it was at rest, and time slows down so much that only 1 hour will pass for the crew, at while on Earth it will take 1.02 hours. At 50% of the speed of light, the Lorentz coefficient will reach 1.15, which is still very small: the mass of the ship at this speed is only 15% greater than at rest, and one hour of time on board is equal to 1.15 hours on Earth. And only at speeds above 80% of the speed of light the Lorentz coefficient begins to increase rapidly. At 87% of the speed of light it reaches 2.00, thus the mass doubles and time slows down by half relative to Earth.

Life on the fast track

The real problem for proponents of interstellar travel is not special relativity, but how to achieve the speeds at which such travel is possible. Even 10% of the speed of light - 30 thousand km per second - far exceeds the speed of the fastest previously launched spacecraft.

In principle, the best rocket fuel is antimatter - the opposite of ordinary matter. The nucleus of an atom of a normal substance is positively charged, and the electrons rotating around it are negatively charged. In antimatter it is the other way around: the nucleus is negative, and the rotating particles, positrons, are positive. When matter and antimatter meet, they mutually destroy each other (annihilate), converting all mass into energy. It turns out that matter and antimatter are powerful fuels, because even a small amount of mass m contains energy E equal to mc2. The speed of light is so high that when multiplied by itself (squared), the amount of energy, even with a small mass of matter or antimatter, will be enormous. If you shake hands with your antimatter counterpart, the resulting energy can power an entire country for several months or send a small spaceship to Alpha Centauri.

Unfortunately, antimatter does not exist on Earth in its natural form, and astronomers do not know its sources in the solar system. Antimatter can be produced by nuclear reactions, but only in very small quantities, so producing even the relatively small amount of antimatter needed to power a spacecraft would require enormous costs. Today, antimatter, even if scientists found a way to mine it, would cost trillions of dollars per ounce.

But any rocket, even one powered by a mixture of matter and antimatter, will encounter a peculiar trap: in order to accelerate the spacecraft, it is necessary to increase the engine power. The more fuel is filled, the higher the weight. To get more energy, you need even more fuel, but then the weight of the rocket will increase, and so on ad infinitum... Therefore, scientists are developing projects that will make it possible to accelerate spaceships without rockets. In 1960, Robert Bussard proposed extracting fuel from space itself. There are hydrogen atoms in outer space. If the ship could collect them and place them in a nuclear reactor, the resulting energy would be enough to replenish its fuel reserves. Unfortunately, in interstellar space there is on average only one hydrogen atom per cubic centimeter, so the ship would have to collect these atoms over a radius of over a hundred or even a thousand miles.

Another project without the use of rockets is to build a ship in the form of a sailboat, propelled by light pressure. Such pressure can be created, for example, by a laser installation located somewhere in space. Since the light pressure is low, lasers must be powerful and their beams must be very narrowly focused. If there were people on board such a ship, they would not be able to control their flight. Instead, they would be at the mercy of laser stations many light years away.

Faster than light

Although such ideas seem difficult to implement or, as critics argue, not feasible at all, at least some of them have attracted the attention of famous physicists. At the same time, even more speculative projects are being put forward by young aspiring physicists. For example, it is assumed that it is possible to shorten the path in space by moving through special spatial tunnels (so-called “worm holes”). Then the spacecraft would not need to travel 4.3 light years to get from the Sun to Alpha Centauri. It's as if we built a tunnel from the US to China through the Earth, instead of taking a longer route across the Earth's surface.

Also, as a fantastic hypothesis, the possibility of moving faster than light is considered. Technically, according to Einstein's special theory of relativity, this is not impossible. At the speed of light, the Lorentz coefficient is infinite, but when this speed is exceeded, it becomes, as mathematicians say, imaginary (like, for example, the square root of a negative number) and, as the speed of the ship increases, it decreases. How to overcome this speed barrier when the Lorentz coefficient becomes infinite is unknown, and if this does happen, then returning back to a speed less than the speed of light may be completely impossible. Particles that exceed the speed of light are called tachyons, but no one has ever seen them, leading to speculation that they do not exist in nature. Perhaps there is a parallel Universe in which everything moves faster than light, and its inhabitants strive for a “slower” life. Then maybe we could make a "deal" with them.

But as long as we know nothing about such a Universe, scientists are forced to conquer the one they know. As a first step toward actual interstellar travel, scientists have envisioned launching powered vehicles that would travel fast and far enough to test some concepts about stellar travel without even reaching the nearest stars. The spacecraft proposed for this is called TAU (Thousand Astronomical Units, one thousand astronomical units); he will have to conduct scientific research at a distance of a thousand astronomical units from the Sun, which is 25 times the average distance to Pluto. It would take the ship about a century to travel that distance, which would be only 1% of the total distance to Alpha Centauri. Nevertheless, TAU can rightfully be considered a pioneer among high-speed ships.

However, there are a lot of doubts about interstellar travel, so much that perhaps critics are right when they claim that no civilization is capable of such expeditions. This explains the fact why we know nothing about those intelligent species that may inhabit our Galaxy. But it would be reckless to downplay the capabilities of the civilization that will inhabit the Earth in the future, not to mention extraterrestrial civilizations, the development of which is perhaps millions or even billions of years ahead of us. In addition, if an exact twin of the Earth is discovered around some nearby star, and this could happen in twenty years, the temptation to explore this world directly from a spacecraft will be irresistible.

Perhaps such an expedition will be carried out during the 21st or 22nd century. If so, then those who believe that intelligent life is widespread in space will be forced to explain why then none of those civilizations did the same and sent an expedition to one of the most promising planetary systems in the Galaxy - ours.

Ken Croswell is an astronomer at the University of California, Berkeley (USA), and the author of the book "In Search of Planets", from which this article was adapted.