Topography, geology and physical
properties of space
The universe is made of 70% vacuum energy, 26% exotic dark matter, 4% ordinary matter (e.g. planets, stars, asteroids) and 0.005% radiation (light, cosmic and gamma rays, X-rays).
The existence and properties of empty space can be determined by experiment. Most of the physical properties of space are paradoxical: space is supposed to be empty, but not an absolute vacuum, containing sizeable amounts of matter, energy and radiation; space is an unwelcoming environment, but it offers endless possibilities for life beyond our world.
“Nothing” is a philosophical concept, accessible to logical analysis. Philosophers have been trying to define it since ancient times (Aristotle). We have come to understand that truly empty space cannot exist (that would mean that no matter would be present and gravitational and electromagnetic fields would be exactly zero). Still, the concept needs further clarification for us to fully understand it.
The nineteenth-century Scottish physicist James Clerk Maxwell gave the following definition for vacuum: “The vacuum is that which is left in a vessel after we have removed everything from it”. This definition still leaves us with an unanswered question: what can’t we remove and how do we know we have removed “everything we can remove”?
The distinction between matter and void had to be abandoned when it was proved that particles can spontaneously appear or disappear in the void without the presence of any particles causing powerful interaction.
Three particles: a proton (p) an antiproton (p-) and a pion (π) form out of nothing and then disappear in the void. According to the theory of fields this type of event occurs all the time. Vacuum is far from being “empty”. It contains an unlimited number of particles that are constantly formed and destroyed.
In physics, “something” is quantified by energy. An enclosed space is empty in a physical sense if it has released all the energy it can. According to Einstein’s formula “E=mc2”, air molecules (with the mass “m”) stand for an amount of energy, and the energy from an enclosed space is removed when the air is pumped out. Any system left alone will release all the energy that the surroundings can absorb, assuming a state of minimum energy (e.g. a pendulum will eventually slow to a stop and hang motionless whatever its initial state; it gives off its energy through friction). In some cases, the physical definition of emptiness may lead to surprising results. For example, a physical system represented by a glass filled with water at 0° Celsius (32° Fahrenheit) will surrender energy in the form of heat when the water passed from liquid state to solid (frozen) state. When it melts, it absorbs energy (the heat of melting), which means that the water in its lowest state of energy is solid. According to Einstein’s formula E=mc2, taking the ice out of the system would further lower its energy. Is there something that we cannot take away from any system without raising its energy?
Fully removing matter and energy from a system is, at the present time, impossible.
Since pure vacuum contains no matter, temperature does not exist, as temperature is a measure of the kinetic energy of particles in a substance.
Space is not a perfect vacuum, and temperatures in space vary from just above 0 K (-459,66 Fahrenheit) to millions of degrees at the center of stars.
Gravity gives shape to apparently featureless space. The hills and valleys it creates will be as important to space settlers as geographical features are to terrestrial settlers. For a relatively small body to escape from the surface of a massive body (a planet or moon), it must be lifted through a gravitational well (the more massive the body, the deeper the well). The Earth’s gravity is 22 times more powerful than that of the Moon. This will be of importance to space colonists. In deciding where to get their resources they will have to take into account that matter can be more easily lifted from the Moon than from the Earth. Lagrangian liberation points can also be fount in the Earth-Moon system. These are points where gravitational forces from the two bodies cancel each other out.
The primary criteria for choosing the site of the colony are ease of access to resources, communication and low transportation costs. Satisfactory balances among them can be achieved by efficiently exploiting the topography of space.
One of the most important sources of energy in space is solar radiation. It consists of charged particles (protons) emitted from the sun and its intensity decreases as distance from the sun increases (as the square of distance from the sun). Another, more constant energy source is cosmic radiation, consisting of heavier particles (e.g. iron nuclei) from other galaxies. Radiation on the surface of a planet consists of solar winds or cosmic radiation that reaches the surface and neutrons and gamma-ray photons released when space radiation particles interact with the planet’s atmosphere and crust.
Outside Earth’s atmosphere, the energy flow from the sun is more steady and intense. 1390W of sunlight pass through every square meter of space directly exposed to the sun, while the maximum amount of light reaching the Earth’s surface is 745W/m2. A square meter of space receives 7.5 times more energy from the sun than an average square meter on Earth because of the day-night alternation on Earth and because sunlight doesn’t fall perpendicularly on the surface of the planet.
The intensity and wavelength of unfiltered sunlight is deadly for humans, but it is, at the same time, one of the most valuable energy sources in space.
The earth’s surface is protected from solar winds and cosmic radiation by the atmosphere and magnetic field. The atmosphere absorbs both space radiation and the gamma rays that are produced by the Earth’s crust. The magnetic field diverts most charged particles to the poles, creating aurora borealis.
Mars has little atmosphere and no magnetic field, so the flow of charged particles anywhere on the surface greatly exceeds that on Earth. There is enough atmosphere to create a neutron field (from the interaction of charged particles with the atmosphere and with the crust), but it isn’t thick enough to absorb the neutrons before they reach the surface. Some neutrons are reflected back toward the surface after interacting with the planet’s crust.
Planets, moons and asteroids make up the main material sources in space. Comets could also be considered material sources, but they are hard to exploit because of their high velocity. Accessibility to these sources is determined by distance and the depth of the gravitational field. The Earth would be an important source of material for a colony situated in the vicinity, especially of hydrogen, nitrogen and carbon, which are not found in sufficient amounts anywhere near our planet. The moons of planets usually have shallow gravitational wells, so they offer an attractive source of materials. The Moon can be a good source of aluminum, iron, titanium, oxygen and silicon. These resources, supplemented with small amounts of a few elements from Earth, can supply a colony with all the materials it needs to sustain life.
Asteroids also have shallow gravitational wells and move in regular orbits. They may contain sizeable amounts of hydrogen, carbon and nitrogen, as well as other minerals and frozen water.
Recent studies revealed that the Universe is expanding at an increasing rate. This discovery seems to confirm Einstein’s idea of “dark matter”, the vacuum energy, which is forcing the expansion of the Universe. After studying this dark energy, proffesors Andrei Linde and Renata Kallosh of Stanford University say that the Universe will stop expanding in 10 to 20 billion years and the influence of dark energy will become neutral and then negative, causing a collapse.
In the 1930s, Paul Dirac, an English physicist, proposed that vacuum contained electromagnetic waves called “zero point energy”, contained in “virtual photons”, which appear out of nothing and the energy to create them is taken from the vacuum until the virtual photon disappears. According to this theory, there is an infinite number of possible photon modes, so the total zero point energy in the vacuum is infinite.
It was suggested that there is a substance called “ether”, present everywhere, even in “empty” space. Energy residing in the ether would be the source for the random emerging and disappearance of particles in the, but there is nothing that permits the growth of large objects. When the energy increases, the number of participating particles increases, but they cannot be joined together, because they disappear as randomly as they appear.
Because an object is uniformly bombarded under most circumstances, the effects of zero point energy in space are not obvious.
Andrei Dan Costea, Flaviu Valentin
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