32

We see signals coming from the Moon all the time because EME has been a thing since after WW2. Every other amateur radio operator knows how to do it and it's very popular. Do check the wiki linked above. The TL;DR for the article is: lots of people use the Moon as a relay for radio signals on purpose and for fun. Those geeks have even created a festivity of ...


14

Yes, if it's cleverly designed: Depends on signal to noise ratio If it's just putting out a "beep", like Sputnik 1, it will attract attention. That's clearly an artificial signal, it stands out to anyone casually looking at the frequency spectrum, its easily detected, and it will attract some investigation. The more random the signal looks, the ...


12

Western Union sets up Japanese or Chinese offices after WW2. With a US occupation force in Japan after the WW2, this could've even been ordered by the US president. The ITA2 system (from 1924 onwards) had 5 bits per character, and was really only suitable for the English language and those sharing its alphabet, it had 2 channels of 32 characters, one for A-Z,...


8

Unnoticed doesn't mean undetected. It can also mean people detect you, but don't care. There are plenty of satellites in orbit transmitting to various people on the ground and to other satellites. Establish a shell corporation allegedly working in a field that would be expected to launch satellites: telecommunications is a classic, of course; earth imagery ...


8

Dead: The difference between preserving living tissue and dead is that you have to keep living tissue viable, while dead tissue you don't. Everything you can do to living tissue, you can do to dead. So by a huge margin, dead tissue is easier. Every preservation technique you can use on organic material, you can use on DEAD tissue, from embalming to ...


8

Running my hand along my face, a few hours after shaving, I feel I can detect the individual hairs. Waiting 10 hours, yeah I can feel more. Next morning, oh lots more. I'd be very confident that I could learn that pattern, especially as it grabs on my hand as a drag it over it, and use it to estimate with good certainty how much time had past. Pity in this ...


6

Digital telegraphy gets an earlier start. 1943 - The Colossus Computer is invented. This is the first digital computer and is used to break codes. timeline diverges.. It is realized that multiple Colossi working in parallel can greatly reduce the time for computation, and the redundancy also reduces the impact of mechanical failures. The parallel ...


6

Excluding "passive systems", like a light sail accelerated from an Earth based laser, have photon propulsion ever been seriously considered for starship drives? Yes. See the Atomic Rockets page on photon rockets. The classic photon rocket is an antimatter-powered drive propelled by gamma rays. Similar drives show up sporadically in science fiction. ...


6

There is a good chance they will be noticed Is anyone watching the moon closely? Thanks to Donald Trump's Space Policy Directive–1 (AKA: "the Boots on the Moon directive"), the answer to this is almost certainly yes. According to this, it is the USA's goal for the "return of humans to the Moon for long-term exploration and utilization". ...


5

The question of stability will produce very different answers depending on the exact parameters of the system, but it seems that there are regions in parameter space of stability and regions of parameter space of instability. The one example of confirmed significant non-coplanarity I know of is $\upsilon$ Andromedae A, a system containing three (and perhaps ...


5

It would have taken cheap telex terminals that could be placed on every desk. In real life, I have had the choice between sending a telex or making a phone call. I had a phone on my desk, but would have to take a telex message to a central communications office. Unless there was some complication such as international calling and time zone differences, it ...


5

Essentially you'd have to invent most of the modern cell phone: an input system and display that doesn't depend on mechanical devices printing things on paper. This was basically the email system of the 1990s. Had cell phones not been developed, a more widespread email system linked to "phones" could have easily replaced a lot of calling. Indeed,...


5

The trouble with all those fringe sciences is that eventually one of them sticks, and becomes real. If we end up building interstellar travel, its a safe bet that 2020 physics says the engine we used was impossible, just as 1850 physics said time dilation of fast moving objects was impossible. That said, I reckon there is one that's feasible within near ...


5

Let's look at historical data. SN 1054 has an estimate of its distance from Earth at 6500 ± 1600 light years. It was visible by day. Then there is SN 1006, which was bright enough to cast shadows! It happened about 7,200 light years away from us. Astronomers from the time estimated its brightness to be ¼ that of a full Moon: Egyptian astrologer and ...


4

The Atomic Rockets page on photon drives conveys that at perfect efficiency in converting reactor power to a collated gamma ray beam (not happening; there will be waste heat, dispersion...), it takes three hundred megawatts of power to produce one newton of thrust. Unless you'd like to have your building-sized spacecraft accelerate with less than a millionth ...


3

This is related to @JohanHagström's suggestion but somewhat "harder". I felt it would be inappropriate to do a "delete all and insert" on his answer. SETI, and the related question of how much recognisable information we're broadcasting to the Universe, and the related SF trope of approaching aliens watching our TV, is predicated on the ...


3

The easiest way to understand this for a maths novice is to leave axial tilt to the end, and just think of this using an abstract sphere for as long as possible. Step 1 - Angle of incidence to power ratio. If we ignore axial tilt, and my crude mspaint, the amount of energy absorbed from the sun for any point on the planet at any given time looks roughly like ...


3

There are 5 effects I think have been overlooked here. First, the obvious uses; Anything a nitrogen canon can do, this can do better, as its maximum pressure seems to he unbounded in the question, and the sphere can easily be placed near or in things to strengthen the directional focus, (we cant use other gasses to build a cone cause they'd mix together). A ...


3

0-24 hours is easy; most men who shave can estimate within around 6 hours by feel. 1-3 days is pretty easy for me to determine number of days (but nothing more precise) by feel. After that, it's just "scruffy" and hard to gauge by feel. For longer periods of time, Agent Jones needs to know his beard's average growth rate...and have a ruler handy......


3

Your signal integrity might improve! Chasly notes this possibly in the comment. I was just reading an article about this. https://www.syfy.com/syfywire/why-is-there-a-normal-galaxy-sitting-at-the-edge-of-the-universe This exceedingly distant galaxy could be viewed on earth because the lensing effect of a black hole in between pulls the light back together. ...


2

This is link to Food preservation types and technique : https://en.wikipedia.org/wiki/Food_preservation The answer it's very difficult, because there are many factor to consider, bacteria, yeast, external agent, wheater condition, moisture, pathogens for a dead flesh, the duration of a dead tissue depends on type of tissue. A good example of food ...


2

Given that the OP has added or clarified a condition to the question: You are too focused on food and livestock. While I indeed need to feed my crew, I need organic matter for other reasons, too. Moreover, I need them to be as close to original as possible. For example, I need most of the DNA and proteins intact and easily accessible for manipulation in ...


2

Dead You can vacuum seal and then irradiate dead tissue to kill everything living inside of it and then store it at a moderately cold temperature to result in only minimal tissue damage. You can then, if you so choose, pop that dead tissue out of the vacuum seal 200 years later and grill it into a steak, assuming that you had steak to start out with. Most ...


2

Checkout Purdue University's online impact effect calculator, at: https://impact.ese.ic.ac.uk/ImpactEarth/ImpactEffects/ Diameter is not the only factor at play. You need to consider angle, density, and depth. A massive asteriod of ice gently brushing past the ocean is of lower consequence than an iron asteroid of the same size hitting granite at a 90 degree ...


2

Yes. Using electrodynamic propulsion. https://www.scientificamerican.com/article/kilometer-long-space-tether-tests-fuel-free-propulsion/ Electrodynamic propulsion relies on a long charged electrodynamic tether. The tether is charged by the spacecraft and by interacting with magnetic fields in space, it can generate propulsion. It still costs energy, but ...


2

Meteor Burst Communications 'might' fit the bill. Wikipedia link The system would be limited in the amount of data that could be sent with each 'burst' transmission (not so much if its Aliens I guess) but even if a suspicious signal was intercepted (and you'd probably have to be looking for it anyway) detecting the point of origin for any particular ...


2

Encryption declassified Telex was how the Lorenz machines communicated. After WWII, the Lorenz and Enigma encoders were kept classified, as was the work of Bletchley Park. Some documents are still not available, but it is widely suspected that these were given to friendly nations who had no crypto themselves, as a "good enough" solution to get them ...


2

Chaotic initial placement of an N-body system results in everything in the sun or oort cloud. So, no. It wont be planar. I've ran a few N-body simulations trying to see what I can get to form, and randomly placing bodies (using c++'s std::normal_distribution) always resulted in a chaotic explosion. Doesn't matter if I modelled 10 bodies or 100 bodies or 1000....


2

I did not see it mentioned anywhere else, so I thought I would add: If you use a parabolic or other type of beam-focusing antenna, it's possible that only someone at or near your receiver location could even detect the signal. Combined with the other obfuscation techniques mentioned in other answers, this could further help conceal your signal.


2

Your world has FTL ships, therefore in your world relativity works differently from how it works in our world as science currently understands it, therefore no hard-science answer can be given. This is the only possible answer to your question as it currently stands. There is an answer, within relativity theory, to the question of how to precisely determine ...


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