We present an overview of the thermal history of the Universe and the sequence of objects (eg. protons, planets, and galaxies) that condensed out of the background as the Universe expanded and cooled.
We plot (1) the density and temperature of the Universe as a function of time and (2) the masses and sizes of all objects in the Universe.
These comprehensive pedagogical plots draw attention to the triangular regions forbidden by general relativity and quantum uncertainty and help navigate the relationship between gravity and quantum mechanics. How can we interpret their intersection at the smallest possible objects: Planck-mass black holes (“instantons”)? Does their Planck density and Planck temperature make them good candidates for the initial conditions of the Universe?
Our plot of all objects also seems to suggest that the Universe is a black hole. We explain how this depends on the unlikely assumption that our Universe is surrounded by zero density Minkowski space.
![Figure 2: Masses, sizes, and relative densities of objects in our Universe. Time-dependent background densities are color-coded as in Figure 1. The diagonal white dashed isodensity lines correspond to the intersections in Figure 1 of the vertical isochron lines with the black density line. Gravity and quantum uncertainty prevent objects of a given mass from being smaller than their corresponding Schwarzschild radius [Equation 6] or Compton wavelength [Equation 7]. Schwarzschild black holes lie on the black diagonal line which is the lower boundary of the “forbidden by gravity” region. The masses and Compton wavelengths of the top quark (t), Higgs boson (Ho), proton (p), electron (e), and neutrinos (ν) are plotted along the Compton ( m ∝ r−1) diagonal line. Among these, the top quark has the smallest Compton wavelength, because it has the largest mass: 173GeVc−2. The smallest possible object is a Planck-mass black hole indicated by the white dot labeled “instanton”20. Its mass and size are (m, r) = (mp, lp). The smallest observable (not yet evaporated) primordial black hole (PBH) that could have survived until today has the same size as a proton21. The large low-mass black dot in the SMBH (super massive black hole) range is the 4 × 106 solar mass black hole at the center of our galaxy22, while the more massive large black dot is Ton 618. The dashed horizontal line at m = mp emphasizes the orthogonal symmetry of black holes (m ∝ r ) and particles (m ∝ r−1). Our Universe is represented by the “Hubble radius” and has a mass and size that places it on the black hole line, seemingly suggesting that our Universe is a massive, low-density black hole (§III A). The black rectangle containing neutron stars (“NS”), white dwarfs (“WD”), and brown dwarfs (“BD”) indicates the size of the parameter space plotted in Figure 3. Less comprehensive versions of this plot can be found20, 23, 24, 25, 26, 27, 28. See the supplementary material for the data used to make this plot56.](/doc/science/2023-lineweaver-figure2-allobjectsintheuniversebymassdensitysizephasediagram.jpg)
Time-dependent background densities are color-coded as in Figure 1. The diagonal white dashed isodensity lines correspond to the intersections in Figure 1 of the vertical isochron lines with the black density line.
Gravity and quantum uncertainty prevent objects of a given mass from being smaller than their corresponding Schwarzschild radius [Equation 6] or Compton wavelength [Equation 7]. Schwarzschild black holes lie on the black diagonal line which is the lower boundary of the “forbidden by gravity” region.
The masses and Compton wavelengths of the top quark (t), Higgs boson (Ho), proton (p), electron (e), and neutrinos (ν) are plotted along the Compton (m ∝ r−1) diagonal line. Among these, the top quark has the smallest Compton wavelength, because it has the largest mass: 173GeVc−2.
The smallest possible object is a Planck-mass black hole indicated by the white dot labeled “instanton”20. Its mass and size are (m, r) = (mp, lp).
The smallest observable (not yet evaporated) primordial black hole (PBH) that could have survived until today has the same size as a proton21. The large low-mass black dot in the SMBH (super massive black hole) range is the 4 × 106 solar mass black hole at the center of our galaxy22, while the more massive large black dot is Ton 618. The dashed horizontal line at m = mp emphasizes the orthogonal symmetry of black holes (m ∝ r ) and particles (m ∝ r−1).
Our Universe is represented by the “Hubble radius” and has a mass and size that places it on the black hole line, seemingly suggesting that our Universe is a massive, low-density black hole (§III A).
The black rectangle containing neutron stars (“NS”), white dwarfs (“WD”), and brown dwarfs (“BD”) indicates the size of the parameter space plotted in Figure 3.
Less comprehensive versions of this plot can be found20, 23, 24, 25, 26, 27, 28. See the supplementary material for the data used to make this plot56.