Future of an expanding universe

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Current observations suggest that the expansion of the universe will continue forever. The prevailing theory is that the universe will cool as it expands, eventually becoming too cold to sustain life. For this reason, this future scenario once popularly called "Heat Death" is now known as the "Big Chill" or "Big Freeze".[1][2]

If dark energy—represented by the cosmological constant, a constant energy density filling space homogeneously,[3] or scalar fields, such as quintessence or moduli, dynamic quantities whose energy density can vary in time and space—accelerates the expansion of the universe, then the space between clusters of galaxies will grow at an increasing rate. Redshift will stretch ancient ambient photons (including gamma rays) to undetectably long wavelengths and low energies.[4] Stars are expected to form normally for 1012 to 1014 (1–100 trillion) years, but eventually the supply of gas needed for star formation will be exhausted. As existing stars run out of fuel and cease to shine, the universe will slowly and inexorably grow darker.[5][6] According to theories that predict proton decay, the stellar remnants left behind will disappear, leaving behind only black holes, which themselves eventually disappear as they emit Hawking radiation.[7] Ultimately, if the universe reaches thermodynamic equilibrium, a state in which the temperature approaches a uniform value, no further work will be possible, resulting in a final heat death of the universe.[8]

  1. ^ Adams, Fred C.; Laughlin, Gregory (1 April 1997). "A dying universe: the long-term fate and evolutionof astrophysical objects" (PDF). Reviews of Modern Physics. 69 (2): 337–372. arXiv:astro-ph/9701131. Bibcode:1997RvMP...69..337A. doi:10.1103/RevModPhys.69.337. ISSN 0034-6861. Archived from the original on 17 May 2021.
  2. ^ "What Is the Ultimate Fate of the Universe?". WMAP's Universe. NASA. 29 June 2015. Retrieved 19 February 2023.
  3. ^ Carroll, Sean M. (2001). "The cosmological constant". Living Reviews in Relativity. 4 (1): 1. arXiv:astro-ph/0004075. Bibcode:2001LRR.....4....1C. doi:10.12942/lrr-2001-1. PMC 5256042. PMID 28179856.
  4. ^ Cite error: The named reference lun was invoked but never defined (see the help page).
  5. ^ Adams, Fred C.; Laughlin, Gregory (1997). "A dying universe: the long-term fate and evolution of astrophysical objects". Reviews of Modern Physics. 69 (2): 337–372. arXiv:astro-ph/9701131. Bibcode:1997RvMP...69..337A. doi:10.1103/RevModPhys.69.337. S2CID 12173790.
  6. ^ Adams & Laughlin (1997), §IIE.
  7. ^ Adams & Laughlin (1997), §IV.
  8. ^ Adams & Laughlin (1997), §VID.