Dark energy and Dark matter are completely undetectable. But somebody’s calculation shows they should be there. So they conclude it’s undetectable.
Very similar to the search for Planet X. A mistake in calculations of observations of Neptune’s orbit predicted a planet would be there. Back then they figured out the calculation did not accurately describe observed reality. That was called the scientific method.
Today, this bunch of clowns would conclude that it’s obvious Planet X is invisible, and would get to work on theories explaining it’s invisibility.
Dark matter, the non-baryonic form, is yet undetected, but they are trying.
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"Weakly interacting massive particles" (or WIMPs) are hypothetical particles that are thought to constitute dark matter.
There exists no clear definition of a WIMP, but broadly, a WIMP is a new elementary particle which interacts via gravity and any other force (or forces), potentially not part of the standard model itself, which is as weak as or weaker than the weak nuclear force, but also non-vanishing in its strength.
Direct detection
Direct detection refers to the observation of the effects of a WIMP-nucleus collision as the dark matter passes through a detector in an Earth laboratory.
While most WIMP models indicate that a large enough number of WIMPs must be captured in large celestial bodies for indirect detection experiments to succeed, it remains possible that these models are either incorrect or only explain part of the dark matter phenomenon.
Thus, even with the multiple experiments dedicated to providing indirect evidence for the existence of cold dark matter, direct detection measurements are also necessary to solidify the theory of WIMPs.
Although most WIMPs encountering the Sun or the Earth are expected to pass through without any effect, it is hoped that a large number of dark matter WIMPs crossing a sufficiently large detector will interact often enough to be seen—at least a few events per year.
The general strategy of current attempts to detect WIMPs is to find very sensitive systems that can be scaled up to large volumes. This follows the lessons learned from the history of the discovery and (by now) routine detection of the neutrino.
https://en.wikipedia.org/wiki/Weakly_interacting_massive_particles
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As for 'dark energy'...
"One explanation for dark energy is that it is a property of space.
Albert Einstein was the first person to realize that empty space is not nothing. Space has amazing properties, many of which are just beginning to be understood.
The first property that Einstein discovered is that it is possible for more space to come into existence.
Then one version of Einstein's gravity theory, the version that contains a cosmological constant, makes a second prediction: "empty space" can possess its own energy.
Because this energy is a property of space itself, it would not be diluted as space expands.
As more space comes into existence, more of this energy-of-space would appear.
As a result, this form of energy would cause the universe to expand faster and faster.
Unfortunately, no one understands why the cosmological constant should even be there, much less why it would have exactly the right value to cause the observed acceleration of the universe."
https://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy