First, let me emphasize that expanding space is not a physical phenomenon. It's a common misconception that there is something like the fabric of space, which expands over time, stretching out systems and carrying objects with it. Expanding space is just a convention that simplifies some of the mathematics in cosmological contexts. It represents a choice of coordinates on spacetime. It is not a physical process.

Since the idea of expanding space is a tenacious misconception, I've put a great deal of further reading at the bottom of this post.

That being said, the universe is expanding, and that means that objects are moving apart in a fairly uniform way, on average. At the largest scales, this expansion seems to be about the same everywhere (homogeneous) and the same in every direction (isotropic), but this is certainly not true at smaller scales. For cosmic voids -- regions less dense than the cosmological average -- their expansion has been slowed less by gravity than the universe at large, so they are expanding faster than average. Conversely, regions that are denser than average expand more slowly, due to their higher self-gravity, and they can even stop expanding and collapse. This collapse process is how galaxies are formed. Galaxies themselves consist of stably orbiting material and hence are not expanding or contracting (except to the extent that they are disturbed by newly accreted material).

Asymmetry in a system and its environment can also exert a tidal influence, which basically means that gravitational forces are different in different directions. This can cause the system to expand at a different rate in different directions, resulting in structures like filaments and sheets in the large-scale structure of the universe.

Regarding expanding space not being a physical influence, see for example this entry in the AskScience FAQ. If you prefer to hear it from eminent cosmologists, here is an excerpt from a 1993 interview with Steven Weinberg and Martin Rees:

> Popular accounts, and even astronomers, talk about expanding space. But how is it possible for space, which is utterly empty, to expand? How can ‘nothing’ expand?

> ‘Good question,’ says Weinberg. ‘The answer is: space does not expand. Cosmologists sometimes talk about expanding space – but they should know better.’

> Rees agrees wholeheartedly. ‘Expanding space is a very unhelpful concept,’ he says. ‘Think of the Universe in a Newtonian way – that is simply, in terms of galaxies exploding away from each other.’

> Narlikar puts it differently. ‘Space is not utterly empty: it has visible matter in the form of galaxies and also a lot of dark matter.’ Weinberg elaborates further. ‘If you sit on a galaxy and wait for your ruler to expand,’ he says, ‘you’ll have a long wait – it’s not going to happen. Even our Galaxy doesn’t expand. You shouldn’t think of galaxies as being pulled apart by some kind of expanding space. Rather, the galaxies are simply rushing apart in the way that any cloud of particles will rush apart if they are set in motion away from each other.’ The matter inside individual galaxies does not take part in the general expansion because it is held together by gravity.

Beyond these, here are articles discussing the point further:

(1) A diatribe on expanding space. This is pretty technical, but it's the most direct attack on the idea of expanding space. One key quote is that

> there is no local effect on particle dynamics from the global expansion of the universe: the tendency to separate is a kinematic initial condition, and once this is removed, all memory of the expansion is lost.

If a system is not expanding, then cosmic expansion is simply not relevant to it.

(2) The kinematic origin of the cosmological redshift. Very well written and less technical, although there are mathematical arguments. The main point of this article is that the cosmological redshift -- often framed as a consequence of space expanding -- is more directly just a Doppler shift. One of the introductory paragraphs reads:

> A student presented with the stretching-of-space description of the redshift cannot be faulted for concluding, incorrectly, that hydrogen atoms, the Solar System, and the Milky Way Galaxy must all constantly “resist the temptation” to expand along with the universe. One way to see that this belief is in error is to consider the problem sometimes known as the “tethered galaxy problem,” in which a galaxy is tethered to the Milky Way, forcing the distance between the two to remain constant. When the tether is cut, does the galaxy join up with the Hubble flow and start to recede due to the expansion of the universe? The intuition that says that objects suffer from a temptation to be swept up in the expansion of the universe will lead to an affirmative answer, but the truth is the reverse: unless there is a large cosmological constant and the galaxy’s distance is comparable to the Hubble length, the galaxy falls toward us. Similarly, it is commonly believed that the Solar System has a very slight tendency to expand due to the Hubble expansion (although this tendency is generally thought to be negligible in practice). Again, explicit calculation shows this belief not to be correct. The tendency to expand due to the stretching of space is nonexistent, not merely negligible.

(3) On The Relativity of Redshifts: Does Space Really "Expand"? The least technical of the batch, this article is also focused on the interpretation of the cosmological redshift. It includes the choice paragraph:

> While it may seem that railing against the concept of expanding space is somewhat petty, it is actually important to set the scene straight, especially for novices in cosmology. One of the important aspects in growing as a physicist is to develop an intuition, an intuition that can guide you on what to expect from the complex equation under your fingers. But if you [are] assuming that expanding space is something physical, something like a river carrying distant observers along as the universe expands, the consequence of this when considering the motions of objects in the universe will lead to radically incorrect results.

Chemical engineer by education, Process engineer in a steel mill by trade (we manufacture electrical steel).

There are no metallurgical differences nor chemical differences to my knowledge. I work in decarburization (carbon removal) and finishing(we anneal then coat the steel in a non conductive coating), but talk to the metallurgists who control the heat chemistry and what they DO care about are

-Carbon

-Manganese

-Phosphorous

-Silicon

-Chromium

-Nickel

-molybdenum

-Titanium

-Copper

-Tin

-Aluminum

-Nitrogen

-Oxygen

-Lead

-Boron

Some of these are only present up to ~3% while others are on the orders of PPM (parts per million) or PPB (parts per billion).

To the original question, any one of these elements being out of wack can ruin the heat and make it a different grade of steel or completely ruin its properties. I have never heard of Iron 54 or 56 ever even mentioned regarding melt chemistries. So I would say this supports a lack of difference both chemically and metalurgically between the isotopes

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This varies wildly depending on the type of trauma, location of damage, and the mechanism, how and what kind of damage occurred.

"Coma" is actually an annoying term, largely because it's super non-specific. It can range from completely unresponsive and brain-dead with few if any central nervous system brain functions and full life support requirements, to persistent vegetative state, where someone may open their eyes, breathe on their own, have reflexes, but otherwise never interact or have meaningful expressions.

"Waking up" is also not a super explicit term, either, because plenty of people open their eyes and are "awake", but after massive brain injuries and trauma, many never recover meaningful function, and simply have reflexive movements, don't track or respond to stimulus properly, etc. Are they truly "awake", or do their eyes just open?

We generally can give people a decent idea of what kind of function to expect after trauma-related swelling, inflammation, blood collection, etc., has receded and resolved, but that can take weeks to months, dependent on the injury. Running various tests like MRIs and CTs to see blood flow to the brain and areas of injury like infarcts or mechanical changes can give us better ideas of the extent of damage, but again, time can change some things and give better pictures.

Very obvious traumas we usually know within a few weeks whether someone will wake up, less time if other organs are involved and/or failing. Less obvious or extensive traumas.. Well, months, sometimes, and even then, the results are mixed, and some "wake-up" more so than others.

When you see signs of hypoxic brain injury on imaging or when multiple organs start to fail, then less likely. When you fully take them off the sedative and paralytic meds inducing the coma, but they don't show any non-reflexive neurological responses or if formal brain death exam is positive then unlikely

To add a note about plants: plants do have nutrient needs just like animals (ex: beets like extra boron). And different plants need different nutrients. And within the same species plants need different nutrients at different times of their lives (vegetative vs. fruiting). It's not just sun, water, air.

Plus plants have many symbiotic relationships with bacteria and fungi in their soils. The plants provide sugars to the soil and the bacteria and fungi help transport nutrients to the root zone. Different plants work with different fungi/bacteria so diversity of plants means diversity of soil biology.

None of this refutes your points, it's just more complex on the plant side than most people think.

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Friend of mine was in a cycle accident at speed was in a “trauma” coma for about six weeks is alive but suffered some brain damage, the brain is very plastic though and was able to re-learn some skills lost from the trauma.

I think the time before it’s likely they won’t ever awaken is very much dependent on the type of injury. The level of brain activity can be monitored in more detail these days and the amount of “activity” and whether it is increasing or decreasing plays a big part.

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What about those old-fashioned iron lung machines from decades ago, didn't people live with those for years?

I don't know for sure, but thinking about how it works for humans I suspect that in many species the hormone levels would be weird for a typical individual of either sex and that might cause infertility. It's usually pretty hard to prove a negative though, I wouldn't be utterly shocked if something fairly basal like a frog might have one set of gametes or the other come out functional.

Would a negative-pressure ventilator like an iron lung solve some of these problems, and if so, is there active research into developing more lightweight alternatives? What about diaphragmatic stimulation?

OP asked about accident-induced coma, while this study specifically excludes trauma-induced comas, concentrating on comas arising from medical conditions like diabetes, heart attack, or stroke.

I looked around a bit, and while I wasn't able to find any relevant papers quite as explicit as this is one, from what I found it doesn't look like the odds of recovery from trauma-induced comas are much better, and they may be worse.

>A single photon strikes an atom, raising its energy level. How many photons are then re-emitted, isotropically?

There's not enough information to determine that; it depends on the level scheme of the atom. If the atom is excited to its first excited state, there can only be one photon emitted. But if it's in a higher excited state, it's possible that multiple photons will be emitted in a cascade.

>To me, wave energy propagation in all directions would no longer have a discrete direction, so how can I conceptualize the "number" of photons re-emitted?

I'm not sure what you mean here, or why you're relating the angular distribution of emitted radiation to the number of photons.

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