1) Eventually the stars and galaxies that define our era will give way to a cosmos of bizarre frozen stars, evaporating black holes, and lonely atoms the size of galaxies.

2) In roughly 1.1 billion years, according to the current theory of stellar evolution, our own Sun will heat up enough to make the Earth inhospitable to life. In 7 billion years, the Sun will become a full-fledged *red giant star, expanding in size to nearly engulf the Earth, and certainly melting the Earth's crust completely and "obliterating every trace of the geology, biology, and civilizations that once graced the planetary surface." A few hundred million years after that, the Sun will exhaust its nuclear fuel, shed its outer layers to become a *white dwarf star, and begin a slow fade to black.

3) In the time frame of 10¹⁰⁰ years, the 10 or 15 billion years already gone by represent an utterly insignificant fragment of time. The significant entries on the cosmic calendar outlined by the authors are as follows:

- 10^-44 seconds: *Big Bang. The indicated time is the Planck time, the quantum unit of time itself, and indivisible.
- 10^-37 seconds: *Inflation begins.
- 10^-34 seconds: Microscopic fluctuations that will become the seeds of galaxies and clusters of galaxies.
- 10^-32 seconds: Inflation ends. An interval of continual expansion and cooling begins, the Universe dominated by smooth, uniform, and dense radiation, with stars and galaxies not yet formed.
- 10^-10 seconds: Electroweak phase transition; the electromagnetic and *weak forces become separate for the first time.
- 10^-5 seconds: *Quarks become confined to form protons and neutrons.
- 10² seconds: Synthesis of light elements.
- 10^5.5 years: Electrons and protons combine to form hydrogen atoms. Universe becomes transparent; *cosmic background radiation breaks free.
- 10⁶ years: First possible stars.
- 10^8.8 years: Formation of galaxies.
- 10¹⁰ to 10^10.1 years: Lifespan of Sun and warm Earth.
- 10¹⁷ years: Most planets are detached from stars.
- 10²⁰ years: Most stars and planets have left galaxies.
- 10²⁵ years: Remaining dark white dwarfs absorb and deplete *weakly interacting massive particles (WIMPS) from galactic halos.
- 10³⁰ years: *Black holes accrete remaining dark white dwarfs and *neutron stars on galaxy-size scales.
- 10³³ years: Black holes accrete remaining stars on cluster-size scales.
- 10³⁷ years: Possible decay of protons. Nothing made of atoms remains.
- 10⁴⁴ years: Possible decay of *axions into photons.
- 10⁴⁶ to 10⁶⁴ years: Black holes the only remaining concentration of mass.
- 10⁶⁵ years: Stellar mass black holes evaporate.
- 10⁸³ years: Million-solar-mass black holes evaporate.
- 10⁹⁹ years: Largest galaxy-mass black holes evaporate; empty era begins.
- 10¹⁰⁸ years: *Positronium formation and decay in a flat universe.

The authors introduce what they call the "Copernican time principle". Just as our planet, and hence humankind, has no special location, the current cosmological epoch has no special place in the vast expanse of cosmic time. The authors state: "This principle thus exorcises the last vestiges of anthropocentric thought."

QY: Fred C. Adams, University of Michigan 313-764-7433.
(Sky & Telescope August 1998) (Science-Week 17 Jul 98)

*white dwarf star: White dwarf stars are extremely dense and compact stars that have undergone gravitational collapse. They are the final stage in the evolution of low-mass stars after they have lost their outer layers. White dwarf stars are about the size of Earth, but with a mass about that of the Sun.

*Big Bang: From the *Big Bang theory, the general cosmological model that proposes that all matter and radiation in the universe originated in an explosion at a finite time in the past.

*Inflation: From the inflationary model of the initial universe. The inflationary model, first proposed by Alan Guth in 1980, proposes that quantum fluctuations in the time period 10^(-35) to 10^(-32) were quickly amplified into large density variations during the "inflationary" 10^(50) expansion of the universe in that time frame.

*weak forces: The weak force, one of the four fundamental forces, occurs between leptons (particles without internal structure, e.g., electrons, neutrinos) and hadrons (particles with internal structure, e.g., neutrons and protons); the weak force is responsible for radioactivity.

*Quarks: A quark is a hypothetical fundamental particle, having charges whose magnitudes are one-third or two-thirds of the electron charge, and from which the elementary particles may in theory be constructed.

*cosmic background radiation: Unresolved radiation from space, the cumulative effect of many unresolved and individually weak discrete sources. One important form is the microwave background radiation which is considered to be due to the "hot" Big Bang. The "hot-Big-Bang" theory is the specific version proposed by George Gamow in the 1940s in which the temperature of matter and radiation decreases with time.

*weakly interacting massive particles (WIMPS): This refers to a hypothetical elementary particle that is a candidate for cosmic dark matter, a stable neutral particle, somewhat heavier than the neutron, that interacts only weakly with ordinary matter.

*Black holes: If the terminal stages of star death leave a remnant star mass greater than 3 solar masses, the ultimate gravitational collapse will produce a black hole, a relativistic singularity. A black hole is a localized region of space from which neither matter nor radiation can escape. The "trapping" occurs because the requisite escape velocity, which can be calculated from the relevant equations, exceeds the velocity of light and is therefore unattainable. Another view of a black hole is that it is a mass that has collapsed to such a small volume that its gravity prevents the escape of all radiation. Space and time essentially have no meaning in a black hole. The boundary of the black hole is called the "event horizon", because any event within the boundary is invisible outside, the invisibility resulting from the fact that no radiation can escape to be detected. The radius of the black hole depends upon how much matter has fallen into the region; it is called the "Schwarzchild radius", and it is usually a few kilometers. However, massive black holes are possible and are thought to be the source of quasars (quasi-stellar objects), which are extremely luminous sources radiating energy over the entire spectrum from x-rays to radio waves, and which are apparently the oldest and most distant objects in the universe. If quasars indeed involve black holes, the radiation is from material just outside the black hole, and not from anything within it. Nothing inside a black hole can get out of it.

*neutron stars: If, following its terminal stages, the remnant mass of a star is between 1.4 and 2 to 3 solar masses, the star will collapse into a neutron star, a body with a radius of 10 to 15 kilometers, with a core so dense that its component protons and electrons have merged into neutrons. The average density of a neutron star is 10^(15) grams per cubic centimeter, and the weight of an object on the surface of a neutron star would be 10^(11) its weight on the surface of the Earth. Neutron stars apparently have an outer shell of iron, but it is iron like no Earth iron, an iron of 4 orders of magnitude greater density. Theory predicts that a neutron star should rotate very rapidly, be extremely hot, and have an intense magnetic field. Pulsars, sources of pulsed radio energy, are evidently spinning neutron stars which emit beams of radiation from their magnetic poles. A few pulsars have been found in binary systems, and the empirical estimated masses of the pulsars are consistent with the masses predicted by neutron star models.

*axions: A hypothetical elementary particle of very low mass and zero charge, and one of the candidates for dark matter in the Universe.

*Positronium: A positron-electron system that lasts for a measurable time before combining to produce annihilation radiation. Positronium can be thought of as an atom analogous to that of hydrogen in which the electron and positron move in orbits about the center of mass halfway between them. A positron is the antiparticle of the electron, with a rest mass equal to that of the electron, but with opposite charge.