In the early 1990's, one thing was fairly certain about the expansion of the Universe. It might have enough energy density to stop its expansion and recollapse, it might have so little energy density that it would never stop expanding, but gravity was certain to slow the expansion as time went on. Granted, the slowing had not been observed, but, theoretically, the Universe had to slow. The Universe is full of matter and the attractive force of gravity pulls all matter together. Then came 1998 and the Hubble Space Telescope (HST) observations of very distant supernovae that showed that, a long time ago, the Universe was actually expanding more slowly than it is today. So the expansion of the Universe has not been slowing due to gravity, as everyone thought, it has been accelerating. No one expected this, no one knew how to explain it. But something was causing it.
Eventually theorists came up with three sorts of explanations. Maybe it was a result of a long-discarded version of Einstein's theory of gravity, one that contained what was called a "cosmological constant." Maybe there was some strange kind of energy-fluid that filled space. Maybe there is something wrong with Einstein's theory of gravity and a new theory could include some kind of field that creates this cosmic acceleration. Theorists still don't know what the correct explanation is, but they have given the solution a name. It is called dark energy.
More is unknown than is known. We know how much dark energy there is because we know how it affects the Universe's expansion. Other than that, it is a complete mystery. But it is an important mystery. It turns out that roughly 68% of the Universe is dark energy. Dark matter makes up about 27%. The rest - everything on Earth, everything ever observed with all of our instruments, all normal matter - adds up to less than 5% of the Universe. Come to think of it, maybe it shouldn't be called "normal" matter at all, since it is such a small fraction of the Universe.
One explanation for dark energy is that it is a property of space. Albert Einstein was the first person to realize that empty space is not nothing. Space has amazing properties, many of which are just beginning to be understood. The first property that Einstein discovered is that it is possible for more space to come into existence. Then one version of Einstein's gravity theory, the version that contains a cosmological constant, makes a second prediction: "empty space" can possess its own energy. Because this energy is a property of space itself, it would not be diluted as space expands. As more space comes into existence, more of this energy-of-space would appear. As a result, this form of energy would cause the Universe to expand faster and faster. Unfortunately, no one understands why the cosmological constant should even be there, much less why it would have exactly the right value to cause the observed acceleration of the Universe.
Another explanation for how space acquires energy comes from the quantum theory of matter. In this theory, "empty space" is actually full of temporary ("virtual") particles that continually form and then disappear. But when physicists tried to calculate how much energy this would give empty space, the answer came out wrong - wrong by a lot. The number came out 10120 times too big. That's a 1 with 120 zeros after it. It's hard to get an answer that bad. So the mystery continues.
Another explanation for dark energy is that it is a new kind of dynamical energy fluid or field, something that fills all of space but something whose effect on the expansion of the Universe is the opposite of that of matter and normal energy. Some theorists have named this "quintessence," after the fifth element of the Greek philosophers. But, if quintessence is the answer, we still don't know what it is like, what it interacts with, or why it exists. So the mystery continues.
A last possibility is that Einstein's theory of gravity is not correct. That would not only affect the expansion of the Universe, but it would also affect the way that normal matter in galaxies and clusters of galaxies behaved. This fact would provide a way to decide if the solution to the dark energy problem is a new gravity theory or not: we could observe how galaxies come together in clusters. But if it does turn out that a new theory of gravity is needed, what kind of theory would it be? How could it correctly describe the motion of the bodies in the Solar System, as Einstein's theory is known to do, and still give us the different prediction for the Universe that we need? There are candidate theories, but none are compelling. So the mystery continues.
The thing that is needed to decide between dark energy possibilities - a property of space, a new dynamic fluid, or a new theory of gravity - is more data, better data.
By fitting a theoretical model of the composition of the Universe to the combined set of cosmological observations, scientists have come up with the composition that we described above, ~68% dark energy, ~27% dark matter, ~5% normal matter. What is dark matter?
We are much more certain what dark matter is not than we are what it is. First, it is dark, meaning that it is not in the form of stars and planets that we see. Observations show that there is far too little visible matter in the Universe to make up the 27% required by the observations. Second, it is not in the form of dark clouds of normal matter, matter made up of particles called baryons. We know this because we would be able to detect baryonic clouds by their absorption of radiation passing through them. Third, dark matter is not antimatter, because we do not see the unique gamma rays that are produced when antimatter annihilates with matter. Finally, we can rule out large galaxy-sized black holes on the basis of how many gravitational lenses we see. High concentrations of matter bend light passing near them from objects further away, but we do not see enough lensing events to suggest that such objects to make up the required 25% dark matter contribution.
However, at this point, there are still a few dark matter possibilities that are viable. Baryonic matter could still make up the dark matter if it were all tied up in brown dwarfs or in small, dense chunks of heavy elements. These possibilities are known as massive compact halo objects, or "MACHOs". But the most common view is that dark matter is not baryonic at all, but that it is made up of other, more exotic particles like axions or WIMPS (Weakly Interacting Massive Particles).
Most self-respecting starships in science fiction stories use antimatter as fuel for a good reason – it’s the most potent fuel known. While tons of chemical fuel are needed to propel a human mission to Mars, just tens of milligrams of antimatter will do (a milligram is about one-thousandth the weight of a piece of the original M&M candy).
Image right: A spacecraft powered by a positron reactor would resemble this artist's concept of the Mars Reference Mission spacecraft. Credit: NASA
However, in reality this power comes with a price. Some antimatter reactions produce blasts of high energy gamma rays. Gamma rays are like X-rays on steroids. They penetrate matter and break apart molecules in cells, so they are not healthy to be around. High-energy gamma rays can also make the engines radioactive by fragmenting atoms of the engine material.
The NASA Institute for Advanced Concepts (NIAC) is funding a team of researchers working on a new design for an antimatter-powered spaceship that avoids this nasty side effect by producing gamma rays with much lower energy.
Antimatter is sometimes called the mirror image of normal matter because while it looks just like ordinary matter, some properties are reversed. For example, normal electrons, the familiar particles that carry electric current in everything from cell phones to plasma TVs, have a negative electric charge. Anti-electrons have a positive charge, so scientists dubbed them "positrons".
When antimatter meets matter, both annihilate in a flash of energy. This complete conversion to energy is what makes antimatter so powerful. Even the nuclear reactions that power atomic bombs come in a distant second, with only about three percent of their mass converted to energy.
Previous antimatter-powered spaceship designs employed antiprotons, which produce high-energy gamma rays when they annihilate. The new design will use positrons, which make gamma rays with about 400 times less energy.
The NIAC research is a preliminary study to see if the idea is feasible. If it looks promising, and funds are available to successfully develop the technology, a positron-powered spaceship would have a couple advantages over the existing plans for a human mission to Mars, called the Mars Reference Mission.
Image left: A diagram of a rocket powered by a positron reactor. Positrons are directed from the storage unit to the attenuating matrix, where they interact with the material and release heat. Liquid hydrogen (H2) circulates through the attenuating matrix and picks up the heat. The hydrogen then flows to the nozzle exit (bell-shaped area in yellow and blue), where it expands into space, producing thrust. Print-resolution copy Credit: Positronics Research, LLC
"The most significant advantage is more safety," said Dr. Gerald Smith of Positronics Research, LLC, in Santa Fe, New Mexico. The current Reference Mission calls for a nuclear reactor to propel the spaceship to Mars. This is desirable because nuclear propulsion reduces travel time to Mars, increasing safety for the crew by reducing their exposure to cosmic rays. Also, a chemically-powered spacecraft weighs much more and costs a lot more to launch. The reactor also provides ample power for the three-year mission. But nuclear reactors are complex, so more things could potentially go wrong during the mission. "However, the positron reactor offers the same advantages but is relatively simple," said Smith, lead researcher for the NIAC study.
Also, nuclear reactors are radioactive even after their fuel is used up. After the ship arrives at Mars, Reference Mission plans are to direct the reactor into an orbit that will not encounter Earth for at least a million years, when the residual radiation will be reduced to safe levels. However, there is no leftover radiation in a positron reactor after the fuel is used up, so there is no safety concern if the spent positron reactor should accidentally re-enter Earth's atmosphere, according to the team.
It will be safer to launch as well. If a rocket carrying a nuclear reactor explodes, it could release radioactive particles into the atmosphere. "Our positron spacecraft would release a flash of gamma-rays if it exploded, but the gamma rays would be gone in an instant. There would be no radioactive particles to drift on the wind. The flash would also be confined to a relatively small area. The danger zone would be about a kilometer (about a half-mile) around the spacecraft. An ordinary large chemically-powered rocket has a danger zone of about the same size, due to the big fireball that would result from its explosion," said Smith.
Another significant advantage is speed. The Reference Mission spacecraft would take astronauts to Mars in about 180 days. "Our advanced designs, like the gas core and the ablative engine concepts, could take astronauts to Mars in half that time, and perhaps even in as little as 45 days," said Kirby Meyer, an engineer with Positronics Research on the study.
Advanced engines do this by running hot, which increases their efficiency or "specific impulse" (Isp). Isp is the "miles per gallon" of rocketry: the higher the Isp, the faster you can go before you use up your fuel supply. The best chemical rockets, like NASA's Space Shuttle main engine, max out at around 450 seconds, which means a pound of fuel will produce a pound of thrust for 450 seconds. A nuclear or positron reactor can make over 900 seconds. The ablative engine, which slowly vaporizes itself to produce thrust, could go as high as 5,000 seconds.
Image right: This is an artist's concept of an advanced positron rocket engine, called an ablative engine. This engine produces thrust when material in the nozzle is vaporized (ablated). In the image, the engine emits blue-white exhaust as thin layers of material are vaporized by positrons in tiny capsules surrounded by lead. The capsules are shot into the nozzle compartment many times per second. Once in the nozzle compartment, the positrons are allowed to interact with the capsule, releasing gamma rays. The lead absorbs the gamma rays and radiates lower-energy X-rays, which vaporize the nozzle material. This complication is necessary because X-rays are more efficiently absorbed by the nozzle material than gamma rays would be. Credit: Positronics Research, LLC
One technical challenge to making a positron spacecraft a reality is the cost to produce the positrons. Because of its spectacular effect on normal matter, there is not a lot of antimatter sitting around. In space, it is created in collisions of high-speed particles called cosmic rays. On Earth, it has to be created in particle accelerators, immense machines that smash atoms together. The machines are normally used to discover how the universe works on a deep, fundamental level, but they can be harnessed as antimatter factories.
"A rough estimate to produce the 10 milligrams of positrons needed for a human Mars mission is about 250 million dollars using technology that is currently under development," said Smith. This cost might seem high, but it has to be considered against the extra cost to launch a heavier chemical rocket (current launch costs are about $10,000 per pound) or the cost to fuel and make safe a nuclear reactor. "Based on the experience with nuclear technology, it seems reasonable to expect positron production cost to go down with more research," added Smith.
Another challenge is storing enough positrons in a small space. Because they annihilate normal matter, you can't just stuff them in a bottle. Instead, they have to be contained with electric and magnetic fields. "We feel confident that with a dedicated research and development program, these challenges can be overcome," said Smith.
If this is so, perhaps the first humans to reach Mars will arrive in spaceships powered by the same source that fired starships across the universes of our science fiction dreams.
NASA Goddard Space Flight Center
NASA asked companies what they want to do in space over the next few decades, and interest in the moon was high.
CAPE CANAVERAL, Fla. — Corporate researchers may be living on the moon by the time NASA astronauts head off to visit an asteroid in the 2020s, a study of future human missions unveiled on Thursday shows.
The study by Bigelow Aerospace, commissioned by NASA, shows "a lot of excitement and interest from various companies" for such ventures, said Robert Bigelow, founder and president of the Las Vegas-based firm.
The projects range from pharmaceutical research aboard Earth-orbiting habitats to missions to the moon's surface, he said on Thursday, citing a draft of the report due to be released in a few weeks.
NASA intends to follow the International Space Station program with astronaut visits to an asteroid by 2025 and to Mars about a decade later.
President Barack Obama's proposed budget for the fiscal year beginning Oct. 1 requests $105 million for the U.S. space agency to begin work on a mission to find a small asteroid and reposition it around the moon for a future visit by astronauts.
But private companies, including Bigelow Aerospace, have more interest in the moon itself, Bigelow told reporters on a conference call on Thursday.
William Gerstenmaier, NASA's head of space operations, said on the call, "It's important for us to know that there's some interest in moon activity and lunar surface activity."
"We can take advantage of what the private sector is doing" in areas such as space transportation, life support systems and other technologies needed for travel beyond the space station's 250-mile-high orbit, he noted.
NASA typically completes its mission planning before looking at what partnerships and collaborations may be possible, Gerstenmaier added.
"We thought that this time we would kind of turn that around a little bit, that we would ask industry first what they're interested in ... where they see human presence that makes sense, where they see potential commercial markets."
Bigelow Aerospace surveyed about 20 companies as well as foreign space agencies and research organizations for the NASA study, which the company undertook at its own expense. Bigelow has made no secret of its ambition to own, lease and operate inflatable space habitats in Earth orbit and on the moon.
Bigelow handed a draft of the first part of the report to Gerstenmaier on Thursday, 40 days ahead of schedule. The second section, which probes mission planning and other aspects of potential public-private partnerships, is due this fall.
First of all, A heated magentic core equal in mass proportional to the Earth's core is needed. The Gravitational pull would off set the normal orbit of the moon sending it farther away from the earth. This would still be within safe perameter measurements for the purpose intended. In order to create better enviormental conditions for an Earth-like Moon; The earth has the extra elements needed to accomplish this purpose. This type of process would take a very long time to Acomplish!
1. The Circle of the Earth:
It has generally been assumed that the Hebrews considered the earth to be a vast circular plain, arched over by a solid vault-- "the firmament"--above which were stored, as if in cisterns, the "treasuries" (Job 38:22) of the rain, snow and hail, and some writers have even attempted to express this supposed conception in diagrammatic form. One of the best of these attempts, reproduced below, is given by Schiaparelli, in his Astronomy in the Old Testament.
But this assumption is in reality based more upon the ideas prevalent in Europe during the Dark Ages than upon any actual statements in the Old Testament. The same word (chagh) used in the Old Testament to express the roundness of the heavens (Job 22:14) is also used when the circle of the earth is spoken of (Isaiah 40:22), and it is likewise applied to the deep (Proverbs 8:27). Now it is obvious that the heavens are spherical in appearance, and to an attentive observer it is clear that the surface of the sea is also rounded. There is therefore no sufficient warrant for the assumption that the Hebrews must have regarded the earth as flat.
(1) The Earth a Sphere.
Certain astronomical relations were recognized very early. The stars appear as if attached to a globe rotating round the earth once in 24 hours, and this appearance was clearly familiar to the author of the Book of Job, and indeed long before the time of Abraham, since the formation of the constellations could not have been effected without such recognition. But the spherical form of the heavens almost involves a similar form for the earth, and their apparent diurnal rotation certainly means that they are not rigidly connected with the earth, but surround it on all sides at some distance from it. The earth therefore must be freely suspended in space, and so the Book of Job describes it:
"He stretcheth out the north over empty space, and hangeth the earth upon nothing" (Job 26:7).
(2) The North Stretched Out over Empty Space.
Here the "north" signifies the northern circumpolar constellations and the writer recognized that they stretch out beyond the utmost confines of the earth; so that he was not under any impression that the heavens rested upon the earth, or were borne up by mountains. The celestial sphere surrounded the earth entirely, but at a distance from it; between the two there was "empty space." Some commentators have indeed claimed that Job 26:10, "He hath described a boundary upon the face of the waters, unto the confines of light and darkness" is equivalent to a statement that the circumference of the terrestrial plain extended to the place where sea and sky met. But no man of intelligence can, at any time, have supposed that the sea horizon marked the dividing line between day and night, and the meaning of the passage is correctly given in the King James Version, "until the day and night come to an end"; in other words, the waters of the sea will be confined to their appointed place never again to overflow the earth so long as the succession of day and night shall continue (compare Genesis 8:22; 9:15).
(3) The Corners of the Earth.
2. The Pillars of the Earth:
erets, "the earth," is in general the surface of the earth, the dry land inhabited by man and beast. Hence "the pillars" of the earth (Job 9:6) are the rocks that bear up that surface, for as has been shown, it was quite clear to the author of the Book of Job, and to the primitive astronomers, that our world was unsupported in space. For "Vault of the Earth" see \EARTH, VAULT OF\.
3. The Firmament:
(1) The Hebrew Conception.
Above the, spherical earth was stretched out the "firmament" (raqia`) made on the second day of creation to "divide the waters from the waters" (Genesis 16). To the Hebrews the "firmament" was the apparent void above, in which clouds float and the lights of heaven pursue their appointed paths. The word raqia`, by its etymology, suggests an expanse, something stretched, spread or beaten out, as when Isaiah (40:22) says that the Lord "stretcheth out the heavens as a curtain, and spreadeth them out as a tent to dwell in." But the Greek word stereoma, by which the Septuagint rendered raqia`, gives the meaning of a firm and solid structure, and our translators have carried out this same idea in their English rendering of "firmament."
(2) The Alexandrian Conception.
In this however the Septuagint simply expressed the astronomical science of their day as accepted in Alexandria, where the doctrine of a succession of solid crystalline spheres, each carrying a planet, held currency. But in order to express the Hebrew idea, raqia` should be rendered "expanse" or "space"; it corresponds to the "empty space" of Job 26:7. This "expanse" was appointed to divide "the waters which were under the expanse, from the waters which were above the expanse"; and it has been argued from this that the upper waters must have been regarded as being enclosed in a watertight reservoir, furnished with sluices or floodgates, which could be opened to allow the rain to fall.
4. The Windows of Heaven:
Thus in the account of the Flood, "the windows of heaven" are said to have been opened. But, 'arubbah, "window," means a network, or lattice, a form which can never have been ascribed to a literal floodgate; and in the other passages where "the windows of heaven" are mentioned the expression is obviously metaphorical (2 Kings 7:2,19; Isaiah 24:18; Malachi 3:10).
Further the numerous other references to rain connect it with the clouds, as "I will also command the clouds that they rain no rain" (Isaiah 5:6), or in the So of Deborah, "The clouds dropped water" (Judges 5:4; see also Psalms 77:17; 147:8; Proverbs 16:15; Ecclesiastes 12:2). The fantastic idea of solidly built cisterns in the sky furnished with sluices has no warrant in Scripture. So far from any such crude conception, there is a very clear and complete account of the atmospheric circulation. Elihu describes the process of evaporation, "For he draweth up the drops of water, which distilll in rain from his vapor, which the skies pour down and drop upon man abundantly" (Job 36:27,28).
Jeremiah and the Psalmist repeat the description, "He causeth the vapors to ascend from the ends of the earth; he maketh lightnings for the rain, and bringeth forth the wind out of his treasuries" (Jeremiah 10:13). By the foreshortening that clouds undergo in the distance they inevitably appear to form chiefly on the horizon, "at the ends of the earth," whence they move upward toward the zenith. Thus God "calleth for the waters of the sea, and poureth them out upon the face of the earth" (Amos 9:6); and thus "All the rivers run into the sea, yet the sea is not full; unto the place whither the rivers go, thither they go again" (Ecclesiastes 1:7). Other references to the clouds in the Book of Job reveal not merely observation but acute reflection. "Dost thou know the balancings of the clouds, the wondrous works of him who is perfect in knowledge?" (Job 37:16) indicates a perception that the clouds float, each in its own place, at its own level, each perfectly balanced in the thin air.
7. The Deep:
(1) Meaning of the Word.
Tehom, "the deep," means moving water, and hence the ocean, which is represented as being essentially one, exactly as we now know it to be by actual exploration--"Let the waters Under the heavens be gathered together unto one place" (Genesis 1:9). And the earth is stretched out "above the waters" (Psalms 136:6; Psalms 24:2). That is to say that the water surface lies lower than the land surface; and not only so, but, within the substance of the earth itself, there are subterranean waters which form a kind of ocean underground. This also is called in Ezekiel 31:4 the "deep," tehom; "The waters nourished it, the deep made it to grow." But in general tehom denotes the sea, as when Pharaoh's chosen captains were drowned in the Red Sea, "The deeps cover them" (Exodus 15:5). Indeed the word appears to be onomatopoetic derived from the "moaning" or "humming" of the sea; whilst 'erets, the "earth," seems intended to represent the "rattle" of shingle, "the scream of a madden'd beach dragged down by the wave."
(2) The Babylonian Dragon of Chaos.
In Genesis 1, tehom denotes the primeval waters, and the resemblance of the word to Tiamat, the name of the Babylonian she- dragon of Chaos, has led some commentators to ascribe a Babylonian origin to this chapter. It need hardly be pointed out that if this resemblance proves any connection between the Hebrew and Babylonian accounts of creation, it proves the Hebrew to be the original. The natural object, tehom, the sea, must have preceded the mythological personification of it.