Ghideon

My intuitive answer is that your example is about shell theorem. If I remember correctly: Assume a sphere S with charge Q on the surface. Then the electric field outside the sphere of charge is like that of a point charge; the field outside the sphere does not rely on the radius R of the sphere S. Shell theorem implies that another sphere S2 with same charge Q but different radius R2 will have the same field outside as the first sphere S. I do not know if the shell theorem accounts for the dynamics if a single sphere is uniformly modified* to have a different radius but identical center. If the shell theorem holds, so that the behaviour is at all times modelled by a stationary point charge, then there should be no radiation? Did the example contain one sphere changing its radius or two different spheres with identical charge on their surfaces? *) I do not assume that such movement is practically possible, just that the uniform charge Q stays uniform on the surface while R is changed and the whole sphere stays stationary relative the observer.

As far as I know a laser is a device that emits light. Maybe you are looking for electron emitter such as those used in cathode ray tubes?

A free electron laser employs electrons as a gain medium. Photons are emitted, not electrons. edit: x-post

I think @wtf means proof of work in this case. Proof of work* requires that a certain amount of computational effort has been expended for some purpose. Verifiers can subsequently confirm this expenditure with minimal effort on their part. It's a way to deter denial-of-service attacks and other service abuses by requiring some work from a service requester, usually meaning processing time by a computer. Very simplified it is a protection against a Sybil attack where the reputation system (bitcoin in this case) is subverted by creating multiple identities. If this will work in the long run for Bitcoin or other related block chain based applications I do not know. *) Text is based on https://en.wikipedia.org/wiki/Proof_of_work **) Paper: https://link.springer.com/chapter/10.1007%2F978-0-387-35568-9_18

That means that a system consisting of two particles, one "normal" and one "dark", will accelerate? Question: How does that affect conservation of momentum? On a larger scale: what happens to massive objects that get close to the DM halo according to your ideas? When for instance an intergalactic star is getting close the outside edge of a halo of a galaxy, is the star deflected by the halo? What happens to any DM that is affected by the intergalactic star's gravity?

Can you provide som insight in a process allowing that halo to form? From your attached PDF (emphasis mine): (https://www.scienceforums.net/applications/core/interface/file/attachment.php?id=23186) How do you reach an equilibrium instead of a runaway effect?

One trouble is that the first one has unbalanced parentheses:

If I may ask; what is the task in the homework you are working on? Are you, for instance, working on a fiction story or trying to provide a plausible interpretation of the Egyptian stone reliefs? (At the time of writing this is located in the Homework Help section)

After some more reading I think it is kind of the other way around; unbounded nondeterminism states that the amount of delay in servicing a request can become unbounded as a result of arbitration of contention for shared resources while still guaranteeing that the request will eventually be serviced*. With means that by definition, n has to exist. Dijkstra argued that it is impossible to implement systems with unbounded nondeterminism. Hewitt argues that the actor model has the property of unbounded nondeterminism built in, allowing computations that cannot be implemented by Turing Machines. Hewitt has based a justification on metastability of electronics**: "There is no bound that can be placed on how long it takes a computational circuit called an arbiter to settle"****. I have not yet read the Clinger paper*** that according to wikipedia contains a mathematical treatment of the actor model and unbounded nondeterminism. My understanding at this time is that Dijkstra, Hewitt and the actor model is: if the "stop" message is can't be postponed forever why can it still be postponed for an unbounded time? (I am not claiming that your question is wrong, just modifying it to illustrate my understanding) Sources: *) https://en.wikipedia.org/wiki/Unbounded_nondeterminism **) https://en.wikipedia.org/wiki/Metastability_(electronics) ***) https://dspace.mit.edu/bitstream/handle/1721.1/6935/AITR-633.pdf?sequence=2ActorLite ****)https://arxiv.org/vc/arxiv/papers/1008/1008.1459v8.pdf

I think* that is an important part to decide: is the ship included or not? What would benefit the plot most? Once decided there are probably viable options for both cases: A preserved ship due to some circumstances (see for instance answer of @Phi for All). The ship could have been preserved as part of culture or emerging religious movement. Or it could be seen as an important resource; some ruling class of the passengers will guard the ship and try to maintain power by controlling the resources (medicine, metal, knowledge, other ...) Or the ship could be gone because all of it was used (leaning behind old relics, valuable in the current medieval setting). Other options are to let the ship be lost rather than decayed. The landing could have taken place in water or in some mountains where the ship is lost, covered by snow and ice. In the context of chemistry AFAIK the climate have an impact on decay of materials. So one option is to have some property of the planet and the landing spot explain the fate of the ship. For instance an extremely dry desert vs some very humid conditions. For instance acidic** rain could explain how decay of the ship progresses. The above are just some intentionally wildly different examples intended to show that whatever benefits the plot (ship left vs ship destroyed) could be supported by something plausible-looking scenarios without referring to magics. Side note: In a setting where magic is possible there will inherently be events, powers or artefacts that science can't explain? *) Without detailed knowledge about the plot I can only give some rough guesses. **) Not acid, just acidic enough to have a scientifically established effect on the materials of the ship.

I would start by thinking about how the fiction ship survived the trip and how it landed. If the ship had some futuristic properties or features allowing it to cope with radiation, micro meteorites or other hazards in space then the plot may allow for such features to make the ship resistant to the conditions on the planet's surface. My personal opinion: a possible plot hole is why the passengers did not use whatever they could salvage from the ship to make buildings, tools, weapons or whatever.

The CoM of the system as a whole will not move. The CoM of the frame will move which means vibration.

According to my understanding* the computation in the actor model is mathematically proven to be something like this: a program that goes through the sequence (an)n∈N will always terminate since the sequence has a last element. The difference is, I guess, a mathematical difference between unbounded and infinite. In other words, the behaviour of the actor model can be reduced into something like the below pseudocode. It will always terminate at x=n even there is no upper bound for how large n can be: while x<n: x=x+1; The Turing machine on the other hand must contain something like the below, a piece of pseudocode that will not terminate**. while true: x=x+1; *) This is where my knowledge is limited; how to express this in a formally and mathematically correct way that agrees with the mathematical proofs and the science behind the actor model. **) In reality of course there will be a limit for the size of variable x and the program could terminate.

There is evidence of dark matter in galaxies that are observable in visible light. The bullet cluster may be of interest: https://en.wikipedia.org/wiki/Bullet_Cluster.

I do not know the formal mathematics in enough detail but I am interested in discussing this further. Here is an extract about the first case (1): Source: https://arxiv.org/pdf/1008.1459.pdf Second case (2): Source: https://en.wikipedia.org/wiki/Denotational_semantics_of_the_Actor_model As I have limited experience of this so the following (naive) interpretation may be wrong; I am interested in corrections or references: (1): For the turing machine to be unbounded it has to include an nonterminating computation, hence it may not terminate. (2): In the actor model there is no option for the actor to skip the stop message once the message is sent. The computation model allows for the stop message to be delayed/postponed for an unbounded time but eventually it will be handled, hence the computation has to terminate at some point. The computations (but not evidence) are described in https://arxiv.org/vc/arxiv/papers/1008/1008.1459v8.pdf

Computers from the era before transistors used vacuum tubes and they did not spin. But maybe you mean things like the mechanics of punch card devices or rotating drums like the ones used in the Atanasoff-Berry Computer? "Spinning cartridges" sounds like something from a Jacquard machine. I think you are too late; Jacquard created his machines more than 200 years ago (Vintage computers are interesting, and how is this related to the topic of Hewitt and actor model?)

Today I learned the English term antipode. In geography, the antipode of any spot on Earth is the point on Earth's surface diametrically opposite to it. A pair of points antipodal to each other are situated such that a straight line connecting the two would pass through Earth's center.* For example Sevilla in Spain and Auckland in New Zeeland are (approximate) antipodes.** (I got curious about diametrically opposite when reading another thread, thanks @joigus! ) *) https://en.wikipedia.org/wiki/Antipodes **) according to antipodesmap.com

I have not used marine plywood but when working with materials with high risk of tear out and splintering I normally cut oversize and trim with a router. For long cuts I find it easier to get good precision with the router the with sanding. In my case I do not have any saw that can cut to good precision and also not splinter plywood or chip board so I have to cut to oversize and then fix.

@Bill McC The topic is "Spotting Pseudoscience"; is your post meant as an exercise for other members?

Basic question @Bill McC: You seem to claim that mass equals volume. If mass equals volume then a 4 liter tank has the same mass when empty as when it is filled with water, since volume is 4 liters in both cases. Does that match what we observe around us?

Simply because I did not think of it, I did not understand your method enough to see Excel (or graphing software) as part of the solution. And excel number precision is 15 digits* and the method seemed to require more precision to be of practical use. *) Source: The list of specifications at support.microsoft.com/

Thanks for your reply. Can you elaborate on the steps to use to solve a general case; a case constructed in such a way that your method works? I give you the number [math]m[/math]. I know [math]m[/math] is the product of two integers [math]n[/math] and [math]n+2[/math] so your method should be applicable. Please show the steps required to calculate factors [math]n[/math] and [math]n+2[/math] using your method. In other words; in your posts so far I see numerical examples, I would like to see the formulas and steps expressed for any number [math]m[/math] where [math]m[/math] is the product of two integers [math]n[/math] and [math]n+2[/math] as per your statements about the limitations of your method.

Yes and no, I think. My intuitive approach was to not look at the wormhole and just treat B's travel as a "Black Box" according to A. From the point of view of observer A the equations of special relativity should predict the outcome regardless of how B managed to travel. Or in other words; A should be able to apply the equations of SR to the flat spacetime in A's frame of reference and get a valid result. Or leave SR and apply other formulas* but that, in my opinion, deviates too far from the twin paradox But I am not sure my approach is a correct way to try to apply SR in this scenario you have created. (Thanks by the way for an interesting and refreshing discussion!) *) probably General Relativity?

I meant that the answer I gave was quick, sorry for being unclear. But here is a quick one with an attempt at using the time dilation formula to illustrate my quick answer. Time dilation formula: [math]t= \frac{t'}{ \sqrt{1- \frac{ v^{2} }{c^{2} } } } [/math] Assume that an observer "A" , stationary relative to the earth, applies the above formula to calculate the time dilation and/or time experienced by the twin "B" travelling through the wormhole. From A's perspective B moves one lightyear in a very short amount of time (time much less than on year) and hence A uses a velocity v>c in the formula. The result contains the square root of a negative number since [math]1- \frac{ v^{2} }{c^{2} } < 0[/math] and hence SR fails in the scenario.

I find your question interesting! I have not done the math to check this (yet) but I get a feeling that the wormhole introduces a scenario that special relativity does not adress. Does the formulas used to resolve the twin "paradox" apply when faster than light travel is possible? Can an observer, stationary relative to the earth, apply SR to calculate the time experienced by the twin travelling through the wormhole? My reply is a quick intuitive answer and there may be more to your question than I realise at this time.