- Included in the Stephen Hawking Posts List.
- The effects of gravity can be seen by simply looking up at the night sky, where the same side of the Moon is always seen, a phenomenon known as tidal locking.
Martin Winfree
October 8, 2024 ·
Shared with Public
Returning to so-called “negative energy”, I am certainly not a physicist, so all of these posts over the past several years that are responses to concepts and writings and even a mini-series by Stephen Hawking might be missing the boat. Maybe I am making a fool of myself here, and that’s okay. But the whole point of science is to make sense of the world and the Universe around us, and negative energy adds nothing to that understanding for me. Gravity is always on and always relentless; that’s as “positive” as you can get as far as I’m concerned.
The effects of gravity can be seen by simply looking up at the night sky, where the same side of the Moon is always seen, a phenomenon known as tidal locking. Additionally, the Moon originally revolved around the Earth at a much closer distance; these same tidal forces gradually enlarged the orbit of the Moon. For many years, the planet Mercury was thought to be tidally locked relative to the Sun as well; but as described in Wikipedia: “In Mercury’s case, the planet completes three rotations for every two revolutions around the Sun, a 3:2 spin–orbit resonance.”
I think that the real reason Pluto was demoted from a planet to a dwarf planet is that it is much smaller than we originally believed. For the first 50 years after the discovery of Pluto in 1930, it was thought to be larger than Mercury. However, with the discovery in 1978 of Charon, the largest moon of Pluto, its size could be determined more exactly. Pluto actually has roughly one-sixth the mass of the Moon, and one-third its volume; in fact, the Moon is larger than all of the dwarf planets identified so far. I hadn’t known all of this until I researched the information for this post.
Pluto has an eccentric orbit, and for part of the Plutonian “year” (it takes Pluto almost 250 years to complete an orbit around the Sun), it is closer to the Sun than Neptune. While the orbits of Neptune and Pluto do not actually intersect, there is a 2:3 ratio between their orbits, where Pluto orbits the Sun twice over the same period that Neptune orbits the Sun three times. This again is due to the long-term effects of gravity and is known as orbital resonance.
Orbital resonance is present in many other areas of the Solar System. The most remarkable example is that three of the four Galilean moons of Jupiter – Io, Europa, and Ganymede – have a 1:2:4 resonance. Other examples of orbital resonance occur in three pairs of the moons of Saturn. Gaps in the rings of Saturn, including the famous Cassini Division are also caused in large part by orbital resonance.
Difficulties in calculating gravitational forces mean that some examples of orbital resonance are not yet proved. As another example, I discussed previously the “three body problem” in physics that is also the name of a fantastic Chinese science fiction novel that I recently finished reading, The Three Body Problem (2008).
Pluto is located within a region of the Solar System known as the Kuiper Belt, and there is a whole class of minor planets called the “Plutinos” that, like Pluto, have a 2:3 orbital resonance with Neptune. Plutinos constitute about one-quarter of the heavenly bodies identified in the Kuiper Belt to date.
But gravity operates over much larger distances than this. The Sun is of course located in a spiral galaxy known as the Milky Way, although recent mapping indicates that the Milky Way might be a barred spiral galaxy. As I have posted about previously, until the last 100 years or so, the Milky Way was thought to be the only galaxy in the Universe. Now scientists estimate that there are about two trillion galaxies.
Later observations and measurements have determined larger structures even than this. First, there is the “Local Group” surrounding the Milky Way, consisting of its near-twin Andromeda Galaxy and their satellite galaxies, at least 80 galaxies in all. Also, there is the “Local Supercluster”, also known as the Virgo Supercluster, consisting of the Local Group and the Virgo Cluster, composed of at least 100 galaxy groups and clusters.
There are also filaments, sheets, walls, voids, bubbles, and other titanic features that seemingly connect all of this together. Perhaps the most famous is the “Great Attractor” that the Milky Way seems to be moving toward; it even merited a mention in the film Men in Black. The Great Attractor is now identified as the central gravitational point in something called the Laniakea Supercluster covering some 100,000 additional galaxies.
Just this week, I saw a post on the Internet positing that the Milky Way might be part of an even larger structure called the Shapley Concentration. I doubt that there will be any end to this nomenclature considering the availability of new observatories like the James Webb Space Telescope.
By the way, James Webb is a former head of NASA who made a couple of appearances in the marvelous film Hidden Figures about Katherine Johnson and other African American mathematicians and scientists during the early years of the American space program. Webb was portrayed in the film by Jim Strunk. The book Hidden Figures (2016) by Margot Lee Shetterly is a terrific read that I highly recommend.
Finally, gravity also operates over the entire Universe. The question used to be whether or not there was enough gravity in the Universe to reverse the effects of the Big Bang and bring the matter back together in a Big Crunch. Newer measurements show that the expansion of the Universe is increasing, not slowing, and no one has any idea why.
So, one might ask, is there a point to all of this? Not really; I just find it fascinating what gravity is capable of accomplishing given enough time. And I haven’t even brought up black holes. In any case, IMHO gravity is not some idle, potential force that could seriously be described as “negative energy”.