The Astronomy Thread

Ukerric

Ukerric

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Captain Suave said:
Bummer.

I did always wonder how they were going to deal with this issue. Chop at sea is inevitable.
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They have a locking system. Unfortunately, it's designed around Falcon 9 boosters, and the Heavy central cores are slightly larger, which means their locks don't work. So they use a temporary securing system... which isn't good enough.
 
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Mudcrush Durtfeet

Mudcrush Durtfeet

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Ukerric said:
They have a locking system. Unfortunately, it's designed around Falcon 9 boosters, and the Heavy central cores are slightly larger, which means their locks don't work. So they use a temporary securing system... which isn't good enough.
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They've said they'll modify it for the next one. It might be that they wanted to make sure they could do the landings before they spent the money on modifying the locking device.
 
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khorum

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I mean they've been at it for years... it would be weird if they weren't ready for an unmanned test soon. This was made last year but had that upright assembly video recently.

 
Sentagur

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Captain Suave said:
The trick is that mass isn't a concept coupled to volume. Mass is an attribute carried by the Higgs field. What we think of as matter occupies volume due to being dispersed across space by the balance of strong/weak forces vs gravity. Once gravity wins that battle the focus of the Higgs field concentrates in a point. You aren't actually making anything bigger or smaller, you're just changing the distribution of mass over space. (Or maybe space itself concentrates. This is where my pop physics education starts to fail me.)

Matter is 100% empty space. If you could cut open quarks with an infinitely small knife you wouldn't find anything inside them. Matter as we know it is just a phenomenon that occurs when the forces and the Higgs field are balanced within a certain range. It's just different forms of energy repelling and attracting each other, all the way down. That's why E=mc^2, and why particle physicists measure masses in units of energy.

(It's easy enough for me to type this, but it's a complete mindfuck when you think about it in practical terms.)



Density = mass / volume. From an outside observer's perspective, volume is not "removed", exactly. The term just becomes 0 as the mass concentrates due to gravity overwhelming everything else. Holding volume at 0, you can put however much mass you want at that point. Forces go up and the event horizon expands, but nothing actually gets "bigger" due to the addition of more mass because mass does not require or carry space.

From the perspective inside the singularity gravity literally destroys the X, Y, Z, and time dimensions from spacetime and "volume" has no meaning.
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Are you sure about all of this. It sounds like a hypothesis material because at this time we can not examine anything about a black holes and all we have are mathematical models as far as i am aware.
Another point i am having a difficult time wrapping my mind around is the matter=100% empty space claim.
I have seen numbers 99.9999(or more 9s) % but not an even 100%
I get the idea that electrons, protons and neutrons are energy fields in space but at one point of compression wouldnt they start amplifying(or neutralizing) each other instead of just settling into 0 volume space with only the higgs(mass) increasing? Just seems incomplete to me, like we are missing a large chunk of information of what exactly is happening in the singularity.
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Sentagur said:
sounds like a hypothesis
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All scientific claims are hypotheses. Experiments can only prove claims false, not prove claims true. The best we can do is say, "Our observations thus far do not contradict this hypothesis."

Sentagur said:
Another point i am having a difficult time wrapping my mind around is the matter=100% empty space claim.
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I'll admit that statement is too hand-wavy to be strictly true. I came across it in a book recently (I think by Tegmark). Importantly, I believe it only applies in a non-quantum framework. At the quantum level you end up dealing with stuff like Pauli Exclusion Principle and the possible quantization of space at the Plank scale, and in that context it's not correct.

Quantum mechanics is really fucking weird and I don't even pretend to understand it.

Why doesn't matter pass through other matter if atoms are 99.999% empty space?

"The concept of empty space is actually quite tricky, since our intuition "Space is empty when there is no particle in it" differs from the formal "Empty space is the unexcited vacuum state of the theory" quite a lot. The space around the atom is definitely not in the vacuum state, it is filled with electron states. But if you go and look, chances are, you will find at least some "empty" space in the sense of "no particles during measurement". Yet you are not justified in saying that there is "mostly empty space" around the atom, since the electrons are not that sharply localized unless some interaction (like measurements) takes place that actually force them to. When not interacting, their states are "smeared out" over the atom in something sometimes called the electron cloud, where the cloud or orbital represents the probability of finding a particle in any given spot."

Sentagur said:
Just seems incomplete to me, like we are missing a large chunk of information of what exactly is happening in the singularity.
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Yes. No one knows what happens in the singularity. As best we can tell, the laws of physics as we know them cease to operate. Whatever physics is going on in a singularity is unobservable to us.
 
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Sentagur

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Captain Suave said:
All scientific claims are hypotheses. Experiments can only prove claims false, not prove claims true. The best we can do is say, "Our observations thus far do not contradict this hypothesis."
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I get this part. You have observations, then you formulate a hypothesis and then you attempt to falsify it and if it survives a few rounds of that i guess it turns into a theory.
My point was that trying to falsify anything about black holes would be extremely difficult given how we just recently actually confirmed their existence (couple of decades) and we can't examine them directly as far as i am aware.
 
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Sentagur said:
trying to falsify anything about black holes would be extremely difficult
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Yeah. Generally the best we've been able to do is mathematical inference based on implications of the broader models that are our current best guess. The good thing about physics is if it works anywhere, it has to work everywhere (except inside singularities). Of course if it somehow turns out that the laws of physics vary over time or space, we're completely hosed.
 
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iannis

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I believe the "matter is 99% empty space" is becoming an older way to think about it. That is an inescapable fact if you're thinking of matter as particles in space, but it starts to become logically absurd (which is more important than counter-intuitive) if you try to formulate it beyond the vaugeness of language. It's why they're moving into field theories. And they're successfully moving the conceptualization.

But that's going to be a little while before that becomes popularized. If you think about it the general conception of it lags a generation behind the work along the edges.

Matter is mostly empty space is EXACTLY what we were taught, and one way to think about it, but it's high school level insight at this point. By which I mean it's a somewhat educated functional understanding for most purposes but not a very accurate one.

I wrestle with that conceptualization fairly often. I hit it when I do a deep dive on a physics lecture or piece. It's all the interaction of fields. That 'empty' space isn't really empty and that thing we consider as the particle isn't really a particle. That model does work extremely well at and above an atomic scale. You can explain the entirety of chemistry with particles. Below it you begin to get results which that concept cannot explain, and worse, predicts against.

It sounds a little bit like luminous ether to me. But i'm just a dummy.

I might be wrong about this part -- it seems to me like you could rephrase the whole idea of unification as a question, "Why does it change depending on scale?"
 
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meStevo

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khorum

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meStevo said:
Light on details, but a Crew Dragon had an anomaly today during testing, speculated it was during SuperDraco testing, the abort thrusters.

www.nasaspaceflight.com

SpaceX's Crew Dragon spacecraft suffers an anomaly during static fire testing at Cape Canaveral - NASASpaceFlight.com

Just six weeks after splashing down in the Atlantic Ocean following a successful Demo-1 test…
www.nasaspaceflight.com www.nasaspaceflight.com

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That's the crewed flight slated for July or so right? Could they just use a different booster?
 
Ukerric

Ukerric

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khorum said:
That's the crewed flight slated for July or so right? Could they just use a different booster?
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No, it was the capsule used for the fist ISS flight, and scheduled for an emergency abort test. The test was that they'd launch, and then, at Max-Q (just after supersonic, when the worst dynamic effort are exerted and the flight is the most likely to have problem) they'd separate and land the capsule. They were test firing the Draco engines that were going to be used for the abort when the "anomaly" occured.

Apparently, the capsule is a loss.

If they have a spare capsule ready and they can solve quickly what went wrong (possibly problems from the sea touchdown), the testing schedule won't suffer overmuch. Otherwise, we're looking at 2020.
 
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meStevo

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This is neat.


A team of researchers from the Strasbourg Astronomical Observatory, Bologna Observatory and the University of Stockholm has identified a stream of stars that was torn off the globular cluster ω Centauri. Searching through the 1.7 billion stars observed by the ESA Gaia mission, they have identified 309 stars that suggest that this globular cluster may actually be the remnant of a dwarf galaxy that is being torn apart by the gravitational forces of our Galaxy.​
 
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