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That happens only if dark energy is phantom energy, which is not really supported by observations or theory, but can't be definitely ruled out either. Essentially what happens is that in these models, the pressure of the dark energy fluid is sufficiently negative that expansion raises its energy density. With higher energy density, its gravitational repulsion becomes stronger. Eventually the repulsion becomes strong enough to separate atoms.

Rain is liquid water, it'll be more dense than the solid snow. Collect a container of snow and compare it to the weight of the same container of water. Or just melt the snow and see how little water there is in a large volume of snow.

It's real. Snow is significantly less dense than liquid water, so for an identical mass of liquid water, the volume of equivalent snow mass will be much greater than the volume of water. The density, and thus the difference between the amount of snow and the equivalent amount of water (i.e., the snow water equivalent or SWE), is a function of temperature, e.g., this discussion. Generally, as temperature decreases, snow volume for the same SWE goes up, for example the graph on that page highlights that 1 inch (~2.5 cm) of rain can equal ~100 inches (~250 cm) of snow when the temperature is -40 to -21 F (-40 to -29 C) but would only equal ~10 inches (~25 cm) at 28 to 34 F (-2 to 1 C). Importantly, none of these are accounting for compaction of snow after it falls, where the density of snow can increase significantly with increasing accumulation.

Within the framework of general relativity, dark energy induces gravitational repulsion, which essentially accelerates everything away from everything else. That means it accelerates cosmic expansion.

While this repulsion is sometimes framed as a consequence of accelerating expansion, it doesn't really make sense to put the causation in that direction. For example, in Einstein's static universe, there is repulsion, even though the universe is static (because the repulsion balances matter's attractive gravity). It's really just gravitational repulsion arising from the energy density of dark energy (or the cosmological constant).

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> That sounds plausible. So to further and solidify my understanding, space itself is not expanding, just that physical entities (e.g. galaxies and therelike) are moving apart carried by their initial momentum.

Exactly.

> But what I don't quite understand is the notion that this expansion (or motion) seems to accelerate relatively to each other, to a point where distant objects become unreachable for us even with we could travel at the speed of light. Or am I mixing things up here?

Dark energy induces gravitational repulsion, which accelerates the expansion of the universe and also creates a cosmological event horizon. Indeed the mathematics are very similar to that of a black hole, but inverted, so that whereas things too close to a black hole cannot escape, with dark energy, things that are too distant (with respect to any observer) cannot return. (When thinking about unreachable distant objects, it is we who have become too distant from the object.)

Another question: it is often said in, frankly mostly youtube videos, that in the very late universe "the expansion of the universe will rip apart atoms and eventually protons." So is this just completely wrong? I see the statement in your (2) reference saying that atoms do not, in fact have to "resist the temptation” to expand.

I read part of this as "beets like extra bacon" and thought yes, that makes perfect sense lol

As a physicist who works nowhere near this field, this was a really enjoyable read. My first instinct was to ask about the cosmological redshift, which you addressed. But one thing I was concerned about that you didn't address was the accelerating expansion of spacetime.

Saul Perlmutter won the Nobel prize by using supernova standard candles to prove that the expansion of the universe was accelerating. Doesn't this indicate that the expansion of the universe is a real physical phenomenon - and that it certainly isn't just because of things moving generally apart from one another?

And what about all this discussion about the cosmological constant and vacuum energy (I think this is the same thing as my first question)? If the universe itself isn't expanding, why do we discuss a constant energy density throughout space that causes... an expansion.

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There are smaller negative pressure ventilator options like the Cuirass from Hayak medical. This is essentially a barrel-like chamber you wear over your abdomen which creates a vacuum allowing ventilation support. You breathe into a 'negative space' and thus gain support. It has advantages and drawbacks.

I have used this with two patients with Motor Neuron Disease both of which could not cope with positive pressure ventilation via a face mask (NIV) and it worked well, that is to say they had symptomatic relief.

This treatment was done at the patient's home overnight and during the day as their disease progressed. The Cuirass shell itself is cumbersome and the ventilator is large and noisy so this isn't a great option (but the only one we had considering the decision not to have a trach). The only reason it was successful is because both these patients and their families were highly committed and willing to put up with the difficulties of using the device. It's certainly not for everyone.

I asked myself the same question about whether this technology was developing and would improve but I think that as the majority of patients cope with NIV there is no impetus to throw money at negative pressure. Indeed negative pressure ventilation via Cuirass is a less recent development than NIV and I think it's unlikely to improve because NIV is so 'easy'.

Speaking as a specialist nurse in home ventilation so happy to be corrected/expanded upon

Edit: with respect to ventilating neuromuscular patients it very much depends on the condition. I have many patients with Duchene's Muscular Dystrophy who have been on NIV for well over a decade and are coping really well. These patients seem to me more likely to die from their cardiac issues than respiratory when managed well on a ventilator.

Thanks for the response, I really appreciate it.

Maybe my assumption is wrong. Can you tell me if it is true or not that an atom acts as an "isotropic radiator" upon "spontaneous emission" of a previously absorbed photon?

https://en.m.wikipedia.org/wiki/Isotropic_radiator#:~:text=An%20isotropic%20radiator%20is%20a,sphere%20centred%20on%20the%20source.

Here is where I ran across this:

See at 6:24 to 6:40 of this clip... https://youtu.be/SDqCx4FiJSo

Afaik, that depends on how old the patient is. Chances go way down pretty quickly, but there have been near full recoveries surprisingly late. Read a particular case study of a young man with traumatic brain injury where the whole case study has you keep going "this man is so done for" and yet he advised the doctors on the final paper. Mental.

Here, found it: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3902071/

Wouldn't want to be a doctor making such a grave call with such a lack of certainty. Hate idea of giving up on someone who would have made it, but also of keeping a family from moving on for so long for nothing at all, or a patient who won't ever progress beyond opening his eyes and flinching again. "Waking up" is a multistep process, and you can get stuck on any step of the ladder, incl. those where you are not conscious, or can't move. (Ideally, both together, being stuck on just one truly sucks. E.g. locked in syndrome. Or vegetative state patients who are not yet conscious, but start screaming and screaming.)

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That sounds plausible. So to further and solidify my understanding, space itself is not expanding, just that physical entities (e.g. galaxies and therelike) are moving apart carried by their initial momentum.
But what I don't quite understand is the notion that this expansion (or motion) seems to accelarate relatively to each other, to a point where distant objects become unreachable for us even with we could travel at the speed of light. Or am I mixing things up here?

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No. Space doesn;t expand within galaxies, it expands between galaxies, in the empty spaces.

It's not known if space is a physical object. We do not have the ability to see it expand at a microscopic level. (And also we have no way to get outside the galaxy.)

And here you ruined my plan to chop or a finger and grow a clone in the backyard

Animal cells: permeable, squishy, weak yet adaptable Plant cells: rigid, self-contained, angular.

Grafting plants onto other plants is like building with legos, grafting animals to animals is like trying to stack jellyfish into the shape of the eiffel tower. It's a wonder we can even do it at all.

Can you name some examples?