The Hubble Ultra Deep Fields often showcase galaxies from an ancient era that tell us what the early Stelliferous Age was like.

This Timeline of the Universe is a brief summary of the events that have taken place and will take place in the Universe as we know it. This timeline does not attempt to replace other more detailed references, such as the timeline of the Big Bang, but rather it attempts to be a starting point to help those find more detailed information on the how the Universe has evolved and likely may evolve.

The timeline, while illustrated and detailed, can be somewhat misleading. The amount of time it takes for each successive Age and Era to pass increases exponentially as the Universe gets older and older. The Primordial Age was over and done with in 300,000 years. It's been an estimated 13,700,000,000 years since the Big Bang at present, which means the equivalent of 46,000 Primordial Ages have passed since the Universe was born. By the time most stellar formation ceases and the Degenerate Era begins in the distant future, the Universe will be roughly 100,000,000,000,000 years old. That is about 7,000 times older than the Universe is now, so star formation (and even some galaxy formation) can be expected to continue for quite a while. In 10^40 years, all matter that isn't in a Black Hole is expected to have decayed into gamma ray photons through proton decay, which marks the end of the Degenerate Era and the beginning of the Black Hole era. This marks an age 700,000,000,000,000,000,000,000 times older than the Universe is now (and this is a conservative estimate since it may well be that the proton's half-life is longer than 10³⁶ years).

The Big Bang and matter formation

Main article: Timeline of the Big Bang

The Primordial Age - from 0 years to 300,000 years

The Planck Epoch: 10^-43 seconds

The Universe, which includes time, space, and everything in it, begins with the Big Bang 13.7 ± 0.2 billion years ago. Data that pinpointed the Universe's estimated age and when the Big Bang occurred came from NASA's Wilkinson Microwave Anisotropy Probe (WMAP). Extensive supporting data comes from the Hubble Space Telescope, among others. The earliest point of time scientists can theoretically pinpoint is the Planck Epoch, or 10^-43 seconds after the Big Bang, so therefore this period is actually regarded as the Big Bang Era. This moment, though definable, is poorly understood because of what happens to gravity at such high energies and small scales is very complicated to explore. The Grand Unified Theory is a project to define a theoretical construct for quantum gravity and string theory.

The Inflationary Epoch: 10^-37 seconds

The Universe undergoes hyper-inflation, where expasion is greatly speeded up.

The Grand Unification Epoch: 10^-35 seconds

The four forces of the Universe differentiate themselves; gravity, the strong force, the weak force, and the electromagnetic force. The Universe starts off with the Grand Unified Force, which then differentiates into gravity and the electronuclear force. The electronuclear force, in turn, differentiates into the strong force and electroweak force.

WMAP data shows the microwave background radiation variations throughout the Universe from our perspective, though the actual variations are much smoother than the diagram suggests

The Electroweak Epoch: 10^-12 seconds

Finally, the electroweak force differentiates into the weak force and the electromagnetic force.

Note:Currently, particle accelerators can reproduce the conditions that cause these two forces to act the same thereby reproducing the general conditions of the Universe during this epoch, but no farther. No one has experimentally recreated the high-energy states necessary for the electroweak and the strong forces to merge into the electronuclear force.

The Hadron Epoch: 10^-6 seconds

The Lepton Epoch: 1 second

Hydrogen nuclei begin to form, and the process of nuclear fusion begins as more elements such as helium form

The Epoch of Nucleosynthesis: 3 minutes

The universe is too cool for nuclear activity to occur, and at this point the universe consists of about 75% hydrogen, 25% helium and trace amounts of deuterium, lithium, beryllium, and boron. Elements heavier than this do not have time to form before nuclear reactions stop.

The Reionization Epoch: 300,000 years

Light energy from the initial expansion of the Universe stretches out and weakens to the point where matter finally dominates in influence (this is the generally agreed-to end of the Big Bang era). Telescopes are not able to see this far back into the history of the Universe because the deionization of hydrogen caused "empty space" to be opaque to light in most wavelengths. Instead scientists must use particle accelerators and theoretical physics to infer what occurred indirectly. The most direct evidence scientists can measure from the Big Bang is the cosmic microwave background radiation that is uniformly pervasive throughout the Universe. It is thought this background radiation is actually a snapshot of the early Universe and provides the best evidence of the creation of matter during the early epochs.

Galaxy and star formation

This Hubble Space Telescope image shows the Cartwheel Galaxy undergoing active star formation around its edges

The Stelliferous Age - from 10^6 to 10^14 years

The Matter Domination Epoch: 500,000 years

Hydrogen nuclei (protons) capture electrons, forming the first atoms. By now the Universe has created all the matter it will create and the resulting primordial hydrogen and helium are already clumping into primordial galaxies and quasars. Big Bang Era ends as we move into the Stelliferous Era, which continues to this very day.

The Galaxy/Star formation Epoch: Between 100,000,000 and 1,000,000,000 years

The formation of first mature galaxies and quasars begins to occur. Reionization of hydrogen nuclei occurs, allowing the Universe to be transparent to light because of the radiation flooding intergalactic space. This marks as the farthest back in time optical telescopes can see.

Present Time: 13,700,000,000 years

The Stelliferous Era of the Universe continues to this day as galaxies and stars continue to form and die, although the most active period of the Universe has already occurred far in the past.

End of the Stelliferous Age: 100,000,000,000,000 years

Star and galaxy formation eventually ceases, leaving just the oldest stars that eventually burn out. The synthesis of heavy elements stops because fusion eventually ceases, and matter now undergoes slow and inevitable destruction as proton decay starts to set in. All matter is now contained in distributed gas clouds or compact bodies (a class of objects in the Universe that isn't luminous, like planets, black holes, etc.). See also Galaxy formation and evolution for more information on this era.

Near-term future of the Universe - different scenarios

The Big Rip

This scenario is possible only if dark energy increases over time as the Universe expands. It's highly speculative since dark energy is poorly understood and it's questionable if it varies over time to such a degree that it causes every atom in the Universe to tear apart from the inside out. The summary of the theory goes that given enough time, not only do galaxies race away from each other over but eventually so do stars, then planets, and eventually atoms and also their nuclei as dark energy inevitably overtakes the respective forces that hold these things together

The Heat death of the Universe

This scenario is possible only if the Universe achieves either a steady state or a constant expansion. The implication here is that dark energy does not overtake the other forces of nature on a micro-scale over time because of hyper-inflation of the Universe, but it doesn't mean that the Universe won't expand. It may just expand more slowly than in the Big Rip scenario. Due to supernova explosion observations by the Hubble Space Telescope, dark energy is assumed to be the overriding force governing the Universe's fate and is causing it to accelerate in its expansion. It is unknown what this force is and whether it really exists as a real phenomenon. Given observational data however, it seems most likely the Heat death of the universe is the most likely fate

Note: Longer-term timeline discussion for this scenario continues in this article after this section

The Big Crunch

This scenario is possible only if dark energy is ultimately unable to overcome the force of gravity between galaxies, which inevitably leads to the collapse of the Universe. Observational data does not support this theory, though the alternative, dark energy, is somewhat speculative and ill-defined. What occurs after the Big Crunch is also highly speculative, as it is impossible to say what will happen after time ends. The end of the Universe implies the end of both space and time, making theories on the subject of "what happens after" fall into the realm of religion, metaphysics, or philosophy. Possibilities for continuation of existence include the oscillatory universe, the multiverse, and others.

Long-term future for a long-lived Universe

The Degenerate Age - from 10^14 to 10^40 years

Galaxy and Star Formation Ceases: 10^14 years

Stellar formation stops, leaving matter to decay over a very long period of time. The hydrogen fuel used for fusion by stars will be eventually depleted, leaving all matter in the Universe in a compact state populated by the following objects after all stars burn out:

• Planets and planetoids (this category includes asteroids, comets, brown dwarfs, etc.)
• White dwarfs
• Neutron stars
• Quark stars
• Black Holes

Formerly luminous bodies like stars cool and dim, eventually reaching the same temperature as the Universe's microwave background radiation.

Planet are Flung from Orbits: 10^15 years

Over time, the orbits of planets are kicked into other masses (see above) or scattered throughout the Universe due to gravitational perturbations.

Stars are Flung from Orbits: 10^16 years

The same scattering effect happens to stars and their remnants within galaxies, leaving mostly scattered stellar debris and supermassive black holes

An estimated 1/2 of Protons Decay: 10^36 years

If estimates on the half-life of protons are correct, then one-half off all the free-floating matter in the Universe has been converted into gamma radiation through proton decay

All Protons Decay: 10^40 years

If estimates on the half-life of protons are correct, then these particles (and nucleonic neutrons as well) have now undergone roughly 10,000 half-lives. To put this into perspective: There are an estimated 10⁸⁰ protons in the Universe, and the estimated half-life for this particle is 10³⁶ years. That means the proton's numbers have been slashed in half 10,000 times. If one does the math, there are now roughly 10^-3,000 as many protons as there were at the beginning of the Universe. So that means the total number of remaining protons in the Universe at the end of the Degenerate Era would be far less than one (a very tiny fraction something like 3,000 zeroes after the decimal place before the first significant digit). Effectively, all matter is now contained in the only bodies in the Universe immune to proton decay: black holes

Note: This number is based off of loose estimates as the exact value for the half-life of protons is an unknown quantity with only a known lower-bound. The end of the Degenerate Era is meant to mark the end of baryonic matter's influence on the Universe, so the estimate for how long this era will last may change if and when the exact value for proton decay is pinned down. The specific numerical values are not meant to be taken literally, and are provided only for demonstration purposes.

The Black Hole Age - from 10^40 years to 10^100 years

Black Holes Dominate: 10^40 years

Black holes continue to evaporate via Hawking radiation, but this process is very slow. The first to go are the small ones, then the medium sized ones, and eventually the supermassive black holes too eventually decay into photons.

Black Holes Disintegrate: 10^100 years

Few if any black holes remain; virtually all matter is now converted into photons.

See also 10¹⁹ seconds for times further than 3 billion years into the future.

Ultimate fate for a long-lived Universe

The Dark Age - from 10^100 years until 10^150 years

All Black Holes now Disintegrated: 10^150 years

The remaining Black holes evaporate: first the small ones, and then the supermassive black holes. All matter that used to make up the stars and galaxies has now degenerated into photons

The Photon Age - from 10^150 years until the Distant Future

The Universe Achieves Low-Energy State: 10^1000 years and beyond

The Universe now reaches extreme low-energy state. What happens after this is speculative. It's possible a Big Rip event may occur far off into the future, or the Universe may settle into this state forever, achieving true heat death. Extreme low-energy states imply that localized quantum events become major macro-scale phenomenon rather than micro-scale non-events because the smallest pertubations make the biggest difference in this era, so there is no telling what may happen to space or time during this era

References

• Hawking, Stephen, A Brief History of Time, Bantam Press, 1988

See Also

• Creation (theology) for some theological viewpoints of creation
• End of the Universe for theories about possible final fates for the Universe
• Exponential timeline shows all history on one page in ten lines.
• Galaxy formation and evolution talks about the currect era of star and galaxy formation
• History of physics
• History of astronomy
• History of chemistry
• Timeline of the Big Bang goes into the Big Bang Era in more detail
• Ultimate fate of the universe goes into the end-case scenarios in more detail

External Links

• Holtz, Brian (2002). Human Knowledge: Foundations and Limits. Retrieved March 25, 2004.
• PBS Online (2000). From the Big Bang to the End of the Universe - The Mysteries of Deep Space Timeline. Retrieved March 24, 2005.
• Schulman, Eric (1997). The History of the Universe in 200 Words or Less. Retrieved March 24, 2005.
• Space Telescope Science Institute Office of Public Outreach (2005). Home of the Hubble Space Telescope. Retrieved March 24, 2005.