I'm only very casually knowledgeable in QM, but my understanding is that photons are waves that propagate through the electromagnetic field. They are not the medium, the medium is the field.

As for measuring their wavelength, the most classic example is using a double slit to create a wave interference pattern, then measuring that. Lasers make this easiest and most accurate but it's possible to get an idea of the scale of these wavelengths even using white light.

Lastly, wave particle duality and the uncertainty principle don't really work with most "mechanical" interpretations, at least in a general sense. They're helpful if you're thinking about specific aspects of photons and other particles, but the reality is that quantum behavior just has different rules and trying to understand through the lens of more intuitive mechanics just doesn't work all that well a lot of the time.

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The skeleton on echinoderms is classed as an endoskeleton because it is enclosed by the dermis. But it takes the outside shape of the animal rather than an internal structure. The plates themselves exist within the skin, the skin tissue existing above, below, and between the plates.

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If they were close in time, sure. It's hard to imagine a biogenesis event now, for example, because existing life is so ubiquitous that it'd have a hard time competing against everything.

Clearly all the dna of eukaryotes is so related that it cannot be due to chance. But could it be that archae and bacteria formed from separate abiogenesis events?

Or could eukaryotes have formed multiple times? We know that encapsulation of bacteria to form organelles has occurred at least twice, namely for mitochondria and for chloroplasts. Could it be that different eukaryotic kingdoms have mitochondria that are not related?

>If the conditions necessary to spawn life essentially produced a population, rather than an individual, then I don't know that we'd be able to tell the difference without seeing it in action.

Yes this is essentially what I meant, the question whether all life comes from one single cell, of if at some point the conditions were such that many cells formed that were very similar, maybe even with similar dna that was being copied, floating around.

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>Another way to view it: When light is emitted, it is quantized (discrete). It is not continuous. When you turn the dimmer switch on an LED, it doesn't produce a bigger or smaller light beam, it produces a larger or smaller number of photons. Each electron you pass through the LED excites an electron to later decay back to ground state.

Though there is also the other way of altering the energy content of a photon, by impacting its frequency (and by extension wavelength.) It's just not useful for affecting the intensity of visible light.

Since we're explaining the photon's essence, I figured making that explicit might help to avoid further confusion.

Sure, but having an exoskeleton implies you don't have an endoskeleton.

Do you have an area in mind that this might happen? Every environment on Earth that's suitable for organic life's survival seems to already be swarming with microbes

Basically there is a dysfunction and or loss of vmat2 (vesicular transporter) which is important for dopamine to go through reuptake. I learned about it in some neuroscience classes. Without that transporter the dopamine cant reuptake.

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As far as model 1 vs model 2. They're both kind of incorrect. A photon is not like a neutron. Photons are massless (not exactly because they have momentum, but that's the way it goes...) a photon is also not the "medium" through which EM radiation travels. A photon is a way to "quantize" (or break down into the smallest possible unit/packet/measurable piece) a beam of light.

Another way to view it: When light is emitted, it is quantized (discrete). It is not continuous. When you turn the dimmer switch on an LED, it doesn't produce a bigger or smaller light beam, it produces a larger or smaller number of photons. Each electron you pass through the LED excites an electron to later decay back to ground state. This decay emits a photon. The more electrons you pass through the LED, the more photons get produced, these photons constructively interfere to produce a higher intensity light.

Try not to think of a photon like a tiny ball of something. It is just a term to describe a unit of a type of energy.

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Intensity is a measurement of the number of photons arriving times the energy of each photo. The question is asking about a single photon, which is actually meaningful to speak of. Are you saying that the single photon's energy (wavelength/frequency) is changing?

>Re “dosage compensation”, is it generally true that more copies of a gene means more gene expression?

Yes, it is true to varying extents.

Cancer cells often have genetic errors adding extra copies of oncogenes, which helps boost their growth etc. That wouldn't work if everything just got compensated back to baseline.

>Aren’t most genes regulated by homeostatic feedback systems?

There is a fair bit of that, but it wouldn't necessarily compensate fully. It also wouldn't be uniform, so some genes would have relatively more expression compared to others, which itself could have problematic effects.

>And what about the many, many plant species that get along just fine with duplicates or triplicates of their entire genome?

Well, at least those don't skew the relative dosage of different genes. It's still usually lethal in animals though, so it's an interesting question.

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This is, in a way, a simple question, but I think it can have some fun deviations.

So, if you haven't seen it before- here's a famous example of an astronaut dropping a hammer and a feather on the moon, and they hit the ground at the same time. This is an illustration of basic physics. You apply Newton's Second Law, which says F = ma, and you say the force of gravity is equal to mg, so you end up with

F = mg = ma

And so you can cancel m on both sides and just get a = g so you see the acceleration an object undergoes is not dependent on mass, so any object falls the same speed. And on the Moon, that works. And it illustrates the principle perfectly. Of course, there is a reason we did that experiment on the moon and it's so cool- it goes against what we feel should happen. On Earth, you drop a hammer and a feather, and of course they fall at very different speeds. The difference comes from the air resistance on the Earth.

Unlike gravity, air resistance is not a constant. It depends on a couple of things- like the shape of the object, the size of the object (and when we say size, we have to be specific. It's the size of the object in the direction of travel- the part of the object getting hit by the air) and the speed of the object (the faster an object is going, the stronger the air resistance is. The equation for air resistance is captured in the famous drag equation and says Fd = 1/2*p*(v^2)Cd*A where p is air density, v is the velocity through the air, Cd is the drag coefficient, which is dependent on the shape of the object (but not the size) and then A is the "reference area" (which is the surface area of the object in the direction of travel).

So, when in the presence of air, using Newton's second law things look a little different. Now you say:

F = ma = mg - 1/2*p*(v^2)Cd*A

(There is a minus sign between them because gravity and air resistance work in opposite directions, gravity pulls down while air resistance pushes up). Now, you can no longer cancel m because mass isn't in the air resistance equation. So, you can solve for a and say

a = g - 1/2*p*(v^2)Cd*A/m

So, when you look at the above equation, if the object has the same Cd and same A, and the mass gets bigger, then acceleration will be bigger (since the term you're subtracting off gets smaller), so in that case, you would say "the heavier something is, the faster it falls." And the works to a certain point. Say, a child's toy ball filled with air vs a bowling ball. About the same size, same Cd (since Cd is just based on shape) and so about the same area, so the more massive bowling ball falls faster. Or a more dramatic example. A piece of paper, or a piece of plywood cut to the same size. The two objects have the same Cd and A, but the plywood is more massive, so it falls faster.

But of course, a lot of times, when something gets more massive, it also gets bigger, so then A would increase as well. So, really, what matters for two objects the same shape, is the ratio between the surface area and the mass. Now, since volume of a sphere (and thus mass) grows with the radius of the sphere cubed, and surface area only grows with radius squared, a large bowling ball that's made out of the same material as a small one will still fall faster (since the mass to surface area ratio is still higher), but a small, dense bowling ball that still weighs less than a larger, less dense bowling ball, could fall faster.

Now, taking this a step further, we have always been operating under the equation that the force of gravity is just mg which is a really good approximation when the thing that's being dropped is much smaller than the thing it's being dropped on, but if we use Newton's law of gravitation we'll see the equation should really be

Fg = -G*m1*m2/r^2

where G is the gravity constant, m1 and m2 are the two masses, and r is the distance between them. So, this shows, perhaps unintuitively, that when you drop a bowling ball on Earth, the bowling ball is pulling just as hard on the Earth as the Earth is on the bowling ball. However, since F = ma since the forces are the same, but the mass of the Earth is so much bigger than the mass of the bowling ball, the acceleration of the Earth is much much smaller than that of the bowling ball, so the acceleration of the Earth is essentially zero. However, what if instead of dropping a bowling ball on Earth, we dropped Mars? Now, while Mars is still a lot smaller than Earth, isn't not so much smaller that the acceleration of Earth would be essentially zero. So, in this case, if we dropped the Moon on Earth vs dropping Mars on Earth, Earth and Mars would collide quicker than the Moon and Earth (assuming dropped from the same height) because Earth would accelerate more towards Mars than it would towards the Moon, because Mars is a lot more massive than the Moon.

I watched that whole video to see the ping pong ball experiment and am now disappointed.

This may be the simplest answer.

We may just not have been able to observe things long enough to make the determination of how the initial event took place. Even if we ran tests in the perfect environment and were able to replicate those tests 1000 times faster, it would take us a million years to see a single success that took a billion years. What if it happens more than just once (say, a thousand times) in that time period? That's still 1000 years to observe success.

It wasn't until the late 19th century that we could even observe cellular division, so at best we've been at it for 150 years. Not to mention that we haven't been looking/testing for it for very long. We may have a long way to go.

A lot going on here. I think of a photon as a packet of light energy (frequently this is referred to as a "quantum" of light energy). This packet consists of some electromagnetic distortion. This distortion has a wavelength and a frequency. These values are interchangeable due to the speed of light. Additionally, through the speed of light relationship, the energy of the photon is defined by its wavelength and frequency. We can then measure a photon using a photodetector. Think of a photodetector like a solar panel with more precise electronics. When a photon hits the photodetector, it transfers its energy into a semiconductor, the photon energy is absorbed and converted to electrical energy. The electrical energy is measured and then we can work backwards from electrical energy to photon energy to wavelength.

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