Everything posted by swansont
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Dark matter
This is contradictory. If the accelerations cancel, there is net scceleration. We don’t have a sphere, and there is no center. The premise is we have mass uniformly distributed over all space.
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Casimir effect and cosmological constant
A single plate would feel no force. Symmetry tells you this, but also there’s no exclusion of any of the QM modes.
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Dark matter
How? It would all cancel.
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Casimir effect and cosmological constant
AFAICT this is proposing to use the same calculational approach for the cosmological constant as for the casimir effect, in terms of dealing with infinities, i.e. the renormalization.
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Dark matter
Perhaps not. It wouldn’t cause lensing or any net gravitational attraction.
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Dark matter
It appears clumped? If it was clumping easily it would be at the center. Who claimed it was perfectly uniformly distributed?
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What is going on with US news websites?
Top Google hit for daily covid cases is the New York Times, and it gives a graph of daily cases, along with the 7-day average
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Dark matter
AFAIK that’s why. If the only channel is gravitational radiation, then the dissipation is very, very weak. All collisions would be basically elastic.
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Alien origin thought experiment.
Super-earths are not the same as earth-like So they would be visiting the solar system, and we would be able to detect them if they weren’t hiding.
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Dark matter
I don’t think complete reflection is physically possible. Reflection requires a momentum transfer, since the momentum of the light changes, and thus energy transfer. So if energy is lost from the incoming light, the reflection can’t be complete.
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Casimir effect and cosmological constant
I am not aware of this interaction. Can you point to any peer-reviewed literature that says that the cosmological constant interacts with anything? That’s what you said. An equality that you wrote down as an assumption. The casimir effect requires conducting plates, which force a component of the electric field to become zero, something not true in free space.
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Alien origin thought experiment.
If you assume they exist, then “they don’t exist” can’t be part of the thought experiment.
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Casimir effect and cosmological constant
How does that work, physics-wise? It looks like you’re just waving your hands to get the answer you want. How does it “become” the cosmological constant? The casimir force can be derived by applying the conductor boundary conditions to the geometry. If L doesn’t matter then you don’t get that answer.
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Is this example of a "tactical foul" in soccer wrong?
We have ethics for when we expect people to self-police, and others involved to make sure people toe the line. In sports we have referees, because ethics don’t enter into it. If you foul someone, there is a penalty. You have to decide if it’s worth it. The sport makes the penalties harsher in certain situations to reduce the incentive to foul.
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Casimir effect and cosmological constant
I would say your understanding is incorrect. A gap in a conductor in a vacuum will not pass current unless there is sufficient voltage for there form an arc. The impedance of the vacuum is ~377 Ohms. If it were a conductor, having a separation distance has no meaning. If you can make connection it has to be via some physics, not unit analysis I didn’t say it was a force; I used force as an example that unit analysis doesn’t get you a connection between different situations.
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Casimir effect and cosmological constant
The casimir effect is, more precisely, a reduction of the electromagnetic vacuum energy owing to the presence of conducting plates. If you are going to equate this with the cosmological constant, you need to do more than unit analysis. A force is going to have units of force, regardless of the origin of it. You can’t e.g. say an electrostatic force is gravitational, just because they have the same units. IOW your assumption that these are connected would just lead to circular reasoning.
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Casimir effect and cosmological constant
Can you explain what it is you’re trying to show? Just throwing up a bunch of equations isn’t sufficient.
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Why did textbooks get so big?
One data point does not make a trend. Why might a particular publisher change a particular book from two volumes to one? Cost might be a factor. It’s possible that eliminating half of the book cover saves a few bucks. But I can find this as a two-volume set. (13th edition, at least. Later editions include modern physics, so the content is not the same)
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Could someone give me an appropriate criticism for this?
Sure
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Dark matter
Careful - they are not thought to interact via the weak interaction, but via some new method on the scale of, or weaker than, the weak interaction
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STVoy Class 9 Warp Core Energy Generation
One explicit avoidance of outright technobabble was the baryon sweep, which was an attempt to not just make something up http://blogs.scienceforums.net/swansont/archives/1043
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Dark matter
If it could interact electromagnetically it would emit thermal EM radiation. The ability to emit light has implications about how it behaves - easy dissipation of energy would allow it to “clump” more readily. And “dark” is also an acknowledgement that we don’t know what it is, as beecee has noted.
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Dark matter
Part of the reason it’s called dark is because it doesn’t interact electromagnetically, and is thus not visible
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STVoy Class 9 Warp Core Energy Generation
Folks, it’s fiction. Things are made up. There are attempts at continuity and they tried to not botch the science too badly, but at the end of it all, they’re telling a story. A friend from high school spent a year as the TNG science consultant (later was on the writing staff); I complained one time about an episode’s science and he admitted he was overruled because the writers liked the story line. There’s an excellent chance the discussion of the efficiency was to advance the story.
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Electron transfer reactions question (ElectroChemistry)
! Moderator Note Show us what you have done ! Moderator Note Absolutely not. This is homework help