problem Comparison Table

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problem comparison table

Subject is an instance of is a kind of has synonym has definition

cosmological constant problem problem The puzzle of why the cosmological constant has a value which is either zero, or in any case roughly 120 orders of magnitude or more smaller than the value that particle theorists would expect. Particle theorists interpret the cosmological constant as a measure of the energy density of the vacuum, which they expect to be large because of the complexity of the vacuum. See vacuum.

flatness problem problem The puzzle of why the universe today is so close to the boundary between open and closed, that is, why it is almost flat. Equivalently, why should the average mass density today be so close to the critical mass density, but not exactly equal to it? If omega begins bigger than 1, it should get bigger and bigger as time goes on; if it begins smaller than 1, it should get smaller and smaller. For omega to be near 0.1 today, about 10 billion years after the big bang, it had to be extraordinarily close to 1 when the universe was a second old. Some people consider such a fine balance to have been highly unlikely according to the standard big bang model, and thus are puzzled as to why the universe today is almost flat. (See closed universe; critical mass density; flat universe; open universe.)

helium problem problem Poses the question: what physical process caused the current abundance of helium in the Universe?

hierarchy problem problem In the context of grand unified theories, the hierarchy problem is our inability to understand theoretically why the energy scale at which the unification becomes apparent, about 10¹⁶ GeV (billion electron volts), is so much higher than other energy scales of relevance to particle physics, such as the mass/energy of a proton, which is only 1 GeV.

horizon problem problem homogeneity problem Cosmological puzzle associated with the fact that regions of the universe that are separated by vast distances nevertheless have nearly identical properties such as temperature. Inflationary cosmology offers a solution.

magnetic monopole problem problem A problem, discovered by John Preskill in 1979, concerning the compatibility of grand unified theories with standard cosmology. Preskill showed that if standard cosmology were combined with grand unified theories, far too many magnetic monopoles would have been produced in the early universe.

missing mass problem problem The cosmic mass that some scientists hypothesize so that the universe will have the critical density of matter, with an exact balance between gravitational energy and kinetic energy of expansion. Such mass is called missing because it represents about 10 times as much mass as has actually been detected. (See closed universe; critical mass density; dark matter.)

paradox problem A self-contradictory proposition. Paradoxes are most useful when they seem most likely to be true, for it is then that they best serve to expose flaws in the data or reasoning that led to their appearance.

Subject	is an instance of	is a kind of	has synonym	has definition
cosmological constant problem	problem			The puzzle of why the cosmological constant has a value which is either zero, or in any case roughly 120 orders of magnitude or more smaller than the value that particle theorists would expect. Particle theorists interpret the cosmological constant as a measure of the energy density of the vacuum, which they expect to be large because of the complexity of the vacuum. See vacuum.
flatness problem		problem		The puzzle of why the universe today is so close to the boundary between open and closed, that is, why it is almost flat. Equivalently, why should the average mass density today be so close to the critical mass density, but not exactly equal to it? If omega begins bigger than 1, it should get bigger and bigger as time goes on; if it begins smaller than 1, it should get smaller and smaller. For omega to be near 0.1 today, about 10 billion years after the big bang, it had to be extraordinarily close to 1 when the universe was a second old. Some people consider such a fine balance to have been highly unlikely according to the standard big bang model, and thus are puzzled as to why the universe today is almost flat. (See closed universe; critical mass density; flat universe; open universe.)
helium problem	problem			Poses the question: what physical process caused the current abundance of helium in the Universe?
hierarchy problem	problem			In the context of grand unified theories, the hierarchy problem is our inability to understand theoretically why the energy scale at which the unification becomes apparent, about 10¹⁶ GeV (billion electron volts), is so much higher than other energy scales of relevance to particle physics, such as the mass/energy of a proton, which is only 1 GeV.
horizon problem		problem	homogeneity problem	Cosmological puzzle associated with the fact that regions of the universe that are separated by vast distances nevertheless have nearly identical properties such as temperature. Inflationary cosmology offers a solution.
magnetic monopole problem	problem			A problem, discovered by John Preskill in 1979, concerning the compatibility of grand unified theories with standard cosmology. Preskill showed that if standard cosmology were combined with grand unified theories, far too many magnetic monopoles would have been produced in the early universe.
missing mass problem	problem			The cosmic mass that some scientists hypothesize so that the universe will have the critical density of matter, with an exact balance between gravitational energy and kinetic energy of expansion. Such mass is called missing because it represents about 10 times as much mass as has actually been detected. (See closed universe; critical mass density; dark matter.)
paradox		problem		A self-contradictory proposition. Paradoxes are most useful when they seem most likely to be true, for it is then that they best serve to expose flaws in the data or reasoning that led to their appearance.

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