Theoretical astrophysicist Ethan Siegel tries his hand with the notoriously difficult problem of dark energy:
What is remarkable about the evidence for dark energy is how perfectly uniform it is. There is no evidence that there’s more or less dark energy in the space occupied by rich galaxy clusters than in the voids of empty space. There is no evidence that dark energy correlates with density, direction, location, or epoch of the universe. It appears to be perfectly uniform, perfectly homogeneous, and perfectly constant: unchanging throughout space and time. And yet, despite its simplicity, it behaves fundamentally differently from all other known forms of energy.
As the volume of the universe increases — as it expands — the energy density does not change; it remains constant. It’s as though there is something present through all of space that isn’t dependent on anything else: matter density, radiation density, temperature, changes in volume, etc. Although we can measure and quantify its effects on the universe, we cannot say that we understand dark energy’s nature.
Ethan Siegel, “Dark energy might be neither particle nor field” at Big Think (September 21, 2021)
Then what can we say?
It is time to take seriously the idea that dark energy might simply be a property inherent to the very fabric of space. Until we learn how to calculate the zero-point energy of empty space itself, or gain some bizarre, surprising, and unanticipated evidence, this will remain one of the biggest existential questions in all the universe.
Ethan Siegel, “Dark energy might be neither particle nor field” at Big Think (September 21, 2021)
So this is existentialism for physicists, right?
Here’s Sabine Hossenfelder on dark energy in 2019:
First things first, what is dark energy? Dark energy is what causes the expansion of the universe to accelerate. It’s not only that astrophysicists think the universe expands, but that the expansion is actually getting faster. And, here’s the important thing, matter alone cannot do that. If there was only matter in the universe, the expansion would slow down. To make the expansion of the universe accelerate, it takes negative pressure, and neither normal matter nor dark matter has negative pressure – but dark energy has it.
We do not actually know that dark energy is really made of anything, so interpreting this pressure in the normal way as by particles bumping into each other may be misleading. This negative pressure is really just something that we write down mathematically and that fits to the observations. It is similarly misleading to call dark energy “dark”, because “dark” suggests that it swallows light like, say, black holes do. But neither dark matter nor dark energy is actually dark in this sense. Instead, light just passes through them, so they are really transparent and not dark.
Sabine Hossenfelder, “What is dark energy?” at BackRe(Action)
Even Hossenfelder sounds sort of existential on this one.
See also: Rob Sheldon: Are “multiple measurements ”closing in on dark energy? Nope.
Researchers: Either dark energy or string theory is wrong. Or both are. But dark energy is so glitzy! Isn’t it a line of cosmetics already?
Researchers: The symmetrons needed to explain dark energy were not found
Rob Sheldon: Has dark energy finally been found? In pop science mags?
Are recent dark energy findings a blow for multiverse theory?
and
Science at sunset: Dark energy might make a multiverse hospitable to life… if it exists
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Why is this even a question? Some people imagine gremlins and leprechauns, others imagine Dark Energy. The only difference is the CASTE of the Dark Energy fanbase.
As to this comment from Siegel,,:
Well actually, as to option number 2, the idea that dark energy “could be a quantum property of space: the zero-point energy of all the fields in the vacuum of space is not required to be zero but could take on some positive, non-zero value. What we often interpret as quantum fluctuations, or particle-antiparticle pairs popping in and out of existence, could be the cause behind dark energy” is contradicted by several negative results.
First off, “There has been a long debate[142] over the question of whether zero-point fluctuations of quantized vacuum fields are “real” ”
And although some people point to the Casimir Effect as supposedly definitive proof for the existence of vacuum energy (and/or zero point energy, and/or quantum foam).
The fact of the matter is that the Casimir Effect is not definitive proof for the existence of virtual particles (and/or zero point energy, and/or quantum foam). Far from it.
As the following article states, ““Casimir effects can be formulated and Casimir forces can be computed without reference to zero-point energies.,,, In fact, the description in terms of van der Waals forces is the only correct description from the fundamental microscopic perspective,[20][21] while other descriptions of Casimir force are merely effective macroscopic descriptions.”
In fact, besides the fact that the Casimir Effect is not definitive proof for the existence of virtual particles (and/or zero point energy, and/or quantum foam), and as mentioned previously, we now have several negative results that argue against the existence of virtual particles (and/or zero point energy, and/or quantum foam),
The following article was rather dramatic as to what the implications of this line of experimentation means. As the subtitle states, “New observations of extreme astrophysical systems have “brutally and pitilessly murdered” attempts to replace Einstein’s general theory of relativity.”
Thus, we have fairly strong empirical reasons to believe that Siegel’s second postulation about zero point energy being the source of Dark energy is not true.
As to Siegel’s first postulation as to what dark energy might be, i.e. “1. The universe can possess a positive, non-zero cosmological constant, a term perfectly allowable in general relativity. It has to be very, very small, but when you put it in everywhere over the whole universe, it eventually comes to dominate.”
For atheistic astrophysicists, this is, by far, the least desirable option.
As the following article notes, “the implied slightly positive value of the cosmological constant constitutes, in the words of physicist Leonard Susskind (who is an atheist), a “cataclysm,” a “stunning reversal of fortunes”,,, It is literally shaking the entire field of theoretical physics, astronomy and cosmology to its foundations.’
And as the following article quips, the 1 in 10^120 discrepancy between what current theory predicts, and what we actually observe, is “a pretty bad prediction.”
And in the following article, three atheistic astrophysicists argued against there being a ‘true cosmological constant’ since if we lived in a universe with a ‘true cosmological constant’ then that would lead, in their atheistic opinion, to “Disturbing Implications” since it would mean “Arranging the universe as we think it is arranged would have required a miracle.,,,”, and they also stated a true cosmological constant would indicate that, “A unknown agent [external to time and space] intervened [in cosmic history] for reasons of its own.,,,”. and thus, being the good dogmatic atheists that they are, they concluded that “The only reasonable conclusion is that we don’t live in a universe with a true cosmological constant”.
There was a small problem for these atheistic astrophysicists. As Dr. Hugh Ross notes in the following video, Dyson, Kleban, and Susskind ended up withdrawing their paper from consideration when the empirical evidence for a ‘true cosmological constant’ soon became overwhelming.
Moreover, the Bible has been fairly direct and explicit in its ‘prediction’ that God alone is ‘stretching out the heavens’.
For example, here are 11 verses from the Bible, which were written well over 2000 years before the discovery of the finely tuned expansion of the universe, that speak of God ‘Stretching out the Heavens’; Job 9:8; Isaiah 40:22; Isaiah 44:24; Isaiah 48:13; Zechariah 12:1; Psalm 104:2; Isaiah 42:5; Isaiah 45:12; Isaiah 51:13; Jeremiah 51:15; Jeremiah 10:12.
Being a Christian, the following verse is my favorite out of that group of verses since it alludes to Jesus walking on the water.
Verse:
Here is a handy discussion of some of the issuess:
Are Photons & Electrons Particles or Waves? Make up your mind god!
Rather than “Dark Energy”, which Sabine does not like, how about we call it “Occult Energy” as in “hidden”, which is one meaning of the word “occult”. That would then perhaps explain why the world is going to Hell in a handbasket. 🙂
On an even less serious note, if gravity were repulsive instead of attractive, various aspects of gravitation could still work as we experience them, but it might explain the acceleration of the expansion of the Universe: https://thopid.blogspot.com/2014/01/repulsive-gravity.html