The observable Universe is 92 billion light-years in diameter. These pictures put just how large that is in perspective. From a pre-existing state, inflation predicts that a series of universes will be spawned as inflation continues, with each one being completely disconnected from every other one, separated by more inflating space.
One of these "bubbles," where inflation ended, gave birth to our Universe some 13.8 billion years ago, with a very low entropy density, but without ever violating the 2nd law of thermodynamics. Cosmically, humanity is a mere drop in the Universe’s vast ocean. This image, taken from the International Space Station by astronaut Karen Nyberg in 2013, shows the two largest islands on the southern part of the Mascarene Plateau: Réunion, in the foreground, and Mauritius, partially covered by clouds.
To see a human on Earth from the altitude of the ISS, a telescope the size of Hubble would be needed. The scale of a human is less than 1/5,000,000 the scale of Earth, but Earth is just a proverbial drop in the cosmic ocean, with a diameter of only a little over 10,000 kilometers. Our civilization’s entire experience — excepting spaceflight — is confined to our planet: 13,000 km across.
This view of the Earth comes to us courtesy of NASA’s MESSENGER spacecraft, which had to perform flybys of Earth and Venus in order to lose enough energy to reach its ultimate destination: Mercury. Several hundred images, taken with the wide-angle camera in MESSENGER’s Mercury Dual Imaging System (MDIS), were sequenced into a movie documenting the view from MESSENGER as it departed Earth. Earth, an oblate spheroid, rotates roughly once every 24 hours on its axis and moves through space in an elliptical orbit around our Sun.
Even other planets routinely occupy volumes thousands of times greater than Earth. Of the eight planets in our Solar System, the four gas giant worlds are the least dense, with less than half the density of the least dense rocky planet (Mars), and with Saturn being even less dense than water. Stars barely outsize the largest planets, but frequently get much larger.
Brown dwarfs, between about 0.013-0.080 solar masses, will fuse protons+deuterons or deuterons+deuterons into helium-3 or tritium, remaining at the same approximate size as Jupiter but achieving much greater masses. Red dwarfs are only slightly larger but do initiate proton-proton fusion, but even the Sun-like star shown here is not shown to scale; it would have about 7 times the diameter of a low-mass star. Stars can be up to nearly 2000 times the diameter of our Sun within this Universe.
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