Term
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Definition
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Term
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Definition
| number of oscillations per second |
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Term
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Definition
| gamma, x-ray, UV, visible light, infrared, microwave, radio waves |
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Term
| Inverse Square Law for Waves |
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Definition
| Energy flux or intensity falls off with distance (1/r^2) (L/(4pir^2)) |
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Term
| Characteristic color of "light" from atoms |
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Definition
1. Glow of noble gases in gas discharge tubes
2. Flame color |
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Term
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Definition
| Decomposing light/sound into its constituent frequencies |
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Term
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Definition
| An idealized object that absorbs all incident electromagnetic radiation. Perfect absorber of radiation is also most efficient producer of radiation (Kirchhoff) |
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Term
| Blackbody spectrum of light |
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Definition
| Universal shape that depends only on its temperature and NOT on its composition or size |
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Term
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Definition
| When the net force acting on an object or groups of objects is zero, the object or group moves with constant velocity. |
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Definition
| Force=(mass)(acceleration) |
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Term
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Definition
| For any force, there is an equal and opposite reaction force |
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Term
| Newton's Law of Gravitation |
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Definition
| Gravitational force (same as rocks as with planets) between two bodies is given by: (gravitational constant) × (mass of the first object) × (mass of the second object) / distance between the objects squared |
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Term
| Kepler's Laws of Planetary Motion |
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Definition
| The time that a planet takes to orbit its star squared is equal to the size of the orbit cubed |
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Term
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Definition
| Are not absolute quantities (LHC) |
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Term
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Definition
| Mass can be converted to energy and vice-versa. Space is not fixed |
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Term
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Definition
| Distortion/curvature of 4D space-time (apparent position versus true position, solar eclipse experiment) |
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Term
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Definition
| The short paths in curved geometry (not curved) |
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Term
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Definition
| "Lines" parallel at one place eventually cross, the sum of triangle angles greater than 180, shortest distance is a segment of a great circle |
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Term
| Curved Space (hyperbolic) |
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Definition
| Sum of the angles of a triangle less than 180, lines parallel eventually diverge, shortest distance is a piece of hyperbola |
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Term
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Definition
| Perihelion (distance closest to the sun) is shifting over the years. General Relativity |
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Term
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Definition
| As light travels upward (against the force of gravity), it loses energy– as particles do. Light with smaller energy (per photon) has a lower frequency and longer wavelength; therefore, the color of light reddens. Gravitational Time Dilation |
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Term
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Definition
| Multiple images of an object is formed due to deflection of light by gravity |
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Term
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Definition
| Distortion (waves) in spacetime propagates at the speed of light. “Distortion” here denotes a weak spatial nonuniformity in the curvature of spacetime. Oscillation |
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Term
| Gravitational Radiation Example |
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Definition
| Neutron Star Binary: as neutron stars orbit each other, spacetime is distorted periodically. Radiation carries away angular momentum |
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Term
| Laser Interferometer Gravitational wave Observatory |
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Definition
| designed to detect space-time ripples passing by earth |
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Term
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Definition
| Nothing, not even light, can escape the gravity of a black-hole; that is why they are called “black”. Astronomers see black holes in just about every galaxy |
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Term
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Definition
| The boundary between where light can and cannot potentially escape |
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Term
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Definition
| The radius of the event horizon |
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Term
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Definition
| Universe is expanding. He found velocity (v) of a galaxy to be related to its distance (d): v = Ho (Hubble Constant)*d. Can shift equation |
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Term
| Determining Distances to Galaxies |
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Definition
1. Find an object in the galaxy that can be identified unambiguously and whose luminosity is known (standard candle)
2. Measure the apparent brightness of the object
2. Use the Inverse Square Law for the apparent brightness to calculate distance |
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Term
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Definition
| Special class of stars that be used as standard candles. Linear relationship between luminous and pulsation (variable stars) |
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Term
| How to use Cepheid Variable to Measure Distances to a galaxy |
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Definition
1. Measure the light curves of many stars in the galaxy
2. Identify the Cepheid variables from their distinctive light curves.
3. Determine the luminosity of the Cepheids from the Period-Luminosity Relation
4. Calculate their distance from the Inverse Square Law |
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Term
| The Distances to Very Distant Galaxies |
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Definition
| Type Ia supernovae are exploding white dwarfs most likely in a mass transfer that have similar explosions and almost all have identical light curves |
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Term
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Definition
| Determination of velocity. Frequency of a wave depends on source-observer speed. V=cz. v = observed frequency. v(little o) is intrinsic |
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Term
| Radial Velocities of Galaxies |
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Definition
| measured using the Doppler shift. The more distant the galaxy, the higher the speed away from us. |
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Term
| Expansion of the Universe |
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Definition
| Space itself can expand carrying the (almost motionless) galaxies). Big Bang was not a bomb. |
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Term
| What is the universe expanding into? |
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Definition
| Nothing- there is nothing outside to expand into (space is created in the expansion) |
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Term
| Where is the center of expansion? |
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Definition
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Term
| Is our galaxy itself expanding? |
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Definition
| No; gravitationally bound objects don't expand |
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Term
| Distribution of the Universe |
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Definition
| Isotropic and homogeneous on large scale |
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Term
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Definition
4% ordinary matter
22% dark matter (does not emit light and does not interact much)
74% Dark Energy (something mysterious that we know very little about) |
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Term
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Definition
If a particle has no electric charge, and is neutral in regards to strong
nuclear forces then such a particle would be invisible, or dark, to us. These particles have mass & interact gravitationally with normal matter. |
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Term
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Definition
| Where the energy in light is preserved, but the light changes direction |
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Term
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Definition
1. Rotational velocities of spiral galaxies. (The amount of mass required to explain the velocity of rotation in
disk galaxies is typically larger than the mass of stars/gas in the galaxy)
2. Fluctuations in the CMS, and subsequent growth of fluctuations and formation of first stars and galaxies.
3. Temperature of gas in galaxy clusters (the amount of mass required to explain the temperature of the hot gas in galaxy clusters is about 10 times larger than the amount of mass contained in hot gas itself, and in the galaxies.) |
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Term
| Observational detection of Dark Matter using rotation curve of spiral galaxies |
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Definition
| The basic idea is based on Newton's law of gravity |
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Term
| Dark Matter Evidence Part 2 |
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Definition
| Evidence from Rotation curve: despite increasing radius from the center, the rotation speed stays constant |
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Term
| Determining the total mass of the cluster |
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Definition
| The bending of light by the gravity of the cluster, i.e. gravitational lensing, and from the velocity of galaxies in the cluster. |
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Term
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Definition
| Hot gas is NOT collisionless. Dark matter is "collisionless" and can pass through dark matter. |
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Term
| Where is normal matter in the present universe? |
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Definition
Most of the mass is in Hot gas in Clusters of Galaxies & Warm gas in the intergalactic medium clusters of
galaxies. Also cold gas in hydrogen clouds that form galaxies if conditions is right. |
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Term
| Direct Detection of Dark Matter |
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Definition
| Hypothesis: dark matter particles can interact with normal particles. The interaction, however, must be rare, or we would have noticed in laboratories by now. Even a very low-probability collision between a dark matter particle and a normal particle can be detected. (WIMP) |
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Term
| Dark Energy Responsibility |
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Definition
| The expansion of the Universe |
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Term
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Definition
| Type Ia Supernovae found being a little too dim at given expansion velocity (red shift). Universe has undergone recent acceleration and is a little older |
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Term
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Definition
| This total density is larger – by a factor ~4 – than what one gets by adding up contributions of ordinary and Dark matters. This extra component is the DARK ENERGY. |
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Term
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Definition
| Anti-gravity effect. Thought to be the so called cosmological constant. |
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Term
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Definition
| Essentially 3D flat accelerating |
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Term
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Definition
Spherical Surface- Closed Universe
Saddle- Open Universe
Flat Plane- Flat Universe (E=0, p=pcrit) |
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Term
| Expansion of the Universe: Case 2 Universe composed of Dark Energy |
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Definition
| The Universe soon after the big-bang was dominated by Dark energy and underwent an exponential phase of expansion called Inflation... this slowed but in the last 5 billion years it reemerged |
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Term
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Definition
| everything that has a speed close to the speed of light. Energy of each particle of radiation increases with redshift as = (1+z)* energy at the present time. E=hv and v=vo(1+z) |
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Term
| Nucleosynthesis: The origin of Helium |
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Definition
| About 24% of the atoms (by mass) in the universe is helium. Helium can be made is by fusion of hydrogen into helium at the centers of stars. But the amount of helium in the universe is much larger than the helium that could have been made in stars. First minutes after Big Bang, temp reached 1 billion K, the entire universe was a fusion reactor (Big Bang Nucleosynthesis). Had there not been a Big Bang the amount of helium would have been much smaller |
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Term
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Definition
| when the temperature is sufficiently high, particles of rest-mass 'm' are created from photons. Particles and anti-particles are always created in pairs. |
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Term
| neutron/proton relationship |
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Definition
| they transfer into one anotehr |
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Term
| Equilibrium and Freeze Out |
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Definition
| The reaction froze when the universe was ~1s old, the temperature below the threshold for producing e- & e+ and at that point there were ~7 protons for every neutron (because neutrons are a little more massive than protons). |
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Term
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Definition
| Protons and neutrons combine (when the universe was a few minutes old) to produce helium, deuterium & lithium |
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Term
| Elements heavier than lithium were not synthesized in the BB |
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Definition
| Could not synthesize because the density of nuclei was too low. Heavier elements are synthesized by the fusion of stars (colder) |
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Term
| Cold (<.1 Million K) gas clouds in between gas clouds |
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Definition
| Contain most of the ordinary matter in the universe, and we know about these "Lyman-alpha clouds" because of quasars' light reflecting off the hydrogen. |
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Term
| Can we see all the way back to the Big Bang? |
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Definition
| The reason we can see into the past of the universe is that current;y, the universe is nearly transparent, but this was not always so. The universe up until 300,000 years after the big bang was so dense that light could not avoid bumping into (scattering off) electron along the way--> opaque |
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Term
| The last scattering surface |
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Definition
| the surface beyond which we cannot see until the Big Bang. Electrons scatter light and make the Universe opaque. |
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Term
| Ionization of hydrogen atoms |
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Definition
| We need straight lines to see and Ionization of hydrogen atoms into protons and electrons was the main reason for the paid increase in density of electrons and allowed us to see. |
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Term
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Definition
| COBE, Boomerang, Microwave Anisotropy Probe (WMAP), Planck Surveyor |
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Term
| Big Bang/Black Body Spectrum |
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Definition
| The spectrum of the radiation left over from the Big Bang is the same as that of a "Black Body" |
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Term
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Definition
| First subtract Dipole from Milky Way radiation then you can get matter-radiation ratios, age/distance of universe, geometry, (notes) |
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Term
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Definition
| All the irregularities that were present in the universe prior to the epoch of INFLATION were wiped out. This is the reason that the universe we inhabit is homogeneous and isotropic on large scale. Fluctuations lead to galaxies and stars |
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Term
| Gravitational instability and formation of galaxies |
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Definition
| Now there is more over/under density which leads to stars and galaxies |
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Term
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Definition
If the acceleration stays constant, the fate is rather dismal: galaxies will be
pulled infinitely far apart, then even small mass, long-lived stars age and die, protons, neutrons and electrons will decay to photons, black holes will evaporate by Hawking radiation. The result would be an empty Universe filled with dilute radiation.
We know so little about the Dark Energy, that it could do other things.
It could get stronger, leading to a Big Rip with atoms and the very fabric of
space being pulled apart (most physicists think this unlikely).
It could reverse sign and gravitate, leading to the recollapse of the Universe in a Big Crunch. |
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Term
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Definition
the notion that new bubble universes are constantly being born, “inflated”, at locations where quantum fluctuations of
different wavelengths add constructively and hence have large potential energy density to drive inflation and form a new bubble universe. |
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Term
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Definition
| scalar field potential varies randomly in space, and those places where the energy density is sufficiently large undergo exponential expansion giving rise to a new “universe”. |
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