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Forum » SpaceEngine » Science and Astronomy Discussions » Science and Astronomy Questions
Science and Astronomy Questions
midtskogenDate: Friday, 07.10.2016, 16:40 | Message # 811
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Brilliant, Watsis. Accellerated particles experience a universe pretty different from ours.




NIL DIFFICILE VOLENTI
 
WatsisnameDate: Friday, 07.10.2016, 23:28 | Message # 812
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Totally. smile Another fun fact:

If we imagine that particle slamming into Earth, from its frame of reference the Earth's atmosphere (which I'll take to be 100km thick by the convention of where space begins) is only 41 nanometers thick. This is below the limit of what you can see with an optical microscope (~200nm). The whole Earth would be about the thickness of a particle of baker's yeast.

To calculate, the relativistically contracted length equals the length in the rest frame, divided by the dilation factor (gamma).

When two relativistic particles collide, it is not like two spheres hitting each other. It is more like two flat disks hitting each other. We can (indirectly) observe the effects of this in particle accelerators. smile





 
steeljaw354Date: Saturday, 08.10.2016, 01:10 | Message # 813
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Watsisname, How would Earth be different with a moon like the one I suggested on page 54?
 
PlutonianEmpireDate: Saturday, 08.10.2016, 01:27 | Message # 814
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Psychologically speaking, why do a lot of people find disappointment in answers from scientists? Like for example, the answer that we can never ever achieve true FTL like in Star Trek/Star Wars, or the answer that Alf Cen cant have Gas giants like Avatar, or that Astrology is bogus?




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steeljaw354Date: Saturday, 08.10.2016, 01:29 | Message # 815
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PlutonianEmpire, Science has many things unanswered, some believe that what they say is fake since they can't see it for themselves, the roundness of the Earth for example. They want to see what they want to see, not 'boring' answers from scientists.
 
WatsisnameDate: Saturday, 08.10.2016, 06:21 | Message # 816
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Quote PlutonianEmpire ()
Psychologically speaking, why do a lot of people find disappointment in answers from scientists?


A few reasons, I think. The obvious one is that sometimes people like believing things even if they're not supported or even contradicted by evidence, so it can be like science is ruining it for them.

Another is a problem of communication by scientists -- they spend many years working and communicating with one another with a technical jargon, which is hard for most people to access. And it's difficult for scientists to explain complex ideas in common language. The physics program at my college emphasized this difficulty by trying to get students to explain usual physics terms and concepts in common language. It's surprising how difficult it is for students to describe something as simple as 'acceleration' without using words like 'velocity' and 'per'. When you get to more advanced topics, explanations can be so filled with jargon or rely on previous knowledge that it becomes indistinguishable from 'techno-babble', and the people you explain it to might wonder what the heck it all means or how did you figure it out or how do you have any confidence in it or why should it be important to understand? I think this is a very hard problem in popular science reporting, and I have huge respect for people who are skilled at it. I try but think I am not very much good at it. smile

Lastly there are people who think the scientific process takes a lot of the mystery and wonder from nature, and turn it into some cold, mechanical explanation. Which I personally disagree with, and love Feynman's quote on it. I think studying nature and understanding how things work brings me an even stronger sense of wonder than I had before. It makes me more curious and raises new and fascinating questions.

Quote steeljaw354 ()
Watsisname, How would Earth be different with a moon like the one I suggested on page 54?


To be sure I understood correctly, are you saying if the moon has an orbital period about the Earth of 6 days (so a smaller orbit), in addition to the larger mass?

0.0199 Earth masses is about 62% more massive than the Moon, so this would not in itself be a huge change. It would make tides 62% larger. But if its orbital period is just 6 days, then its distance must be reduced to about 140,000km, or 36% of its current orbital distance. This will have a very big effect.

The strength of the tidal force is proportional to the mass of the satellite and inversely proportional to the cube of its distance. Meaning if the moon is brought in to a third of its previous orbital distance, then the tidal force becomes 3^3=27 times stronger. A 62% more massive Moon with 36% less distance would make the lunar tidal force 35 times stronger! The current max tidal change is in the Bay of Fundy, Canada, at 16.3 meters. However, we can't just multiply that by 35 to get the new max tidal change, because part of the tidal change is due to the Sun, not just the Moon. Solar tidal force is about half as strong as the Moon's. This means about two-thirds of the current tidal change is caused by the Moon.

So the new, bigger, closer Moon would raise a maximum tide difference of 16.3*2/3*35 = 380 meters! And more average tidal changes around the world would be about 60 meters.

We can get a rough idea for how much of the world would be subjected to the new tidal change zones by matching maps of global tidal variation to maps of areas affected by sea level rise. Note that coastal tide variation is generally bigger than the variation over open ocean, due to how the tidal surge sloshes around local terrain.

I currently live about 30 meters above sea level on a bay, which experiences tide changes up to about 3 meters. The bay goes down to about 30 meters of depth. In this new Moon scenario, high tides would reach just above my house, and low tides would drain the bay out completely. Wow!





 
PlutonianEmpireDate: Saturday, 08.10.2016, 06:46 | Message # 817
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Actually I can quite relate to the difficulty of explaining the technical jargon I know to the average layman. My roommate, for example, has a hard time understanding the mechanics of just how our season changes even work, and I have had to it at least twice a year.

Quote steeljaw354 ()
They want to see what they want to see, not 'boring' answers from scientists.

Yeah I think this explains a lot of it. I know Ive felt this way a few times myself, unfortunately. wacko





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HuesudoDate: Saturday, 08.10.2016, 08:59 | Message # 818
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Quote PlutonianEmpire ()
or the answer that Alf Cen cant have Gas giants like Avatar

I'm curious about that. Is there a post explaining the reason?
 
JackDoleDate: Saturday, 08.10.2016, 09:35 | Message # 819
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Quote PlutonianEmpire ()
that Astrology is bogus?

I did not know this was scientifically proven!
I do not believe in astrology.
But that stars have an influence on my life, I do not consider it to be more improbable than the quantum entanglement.

Quote PlutonianEmpire ()
that Alf Cen cant have Gas giants like Avatar

Why can Alpha Centauri not have gas giants? (Of course there can be no Unobtanium. Therefore, it is called Unobtanium. If there was an element with the properties, it would not be a Unobtanium.)



The speed of light is, of course, a problem.

I have only understood it (to some extent) when I realized that the speed of light is not the highest speed attainable in the universe, but that it is the only speed that exists in the Universe!

Everything that exists in the universe moves with the speed of light through space-time.

A photon, which moves with the speed of light through the three spatial dimensions, stands still on the time axis.
There is no 'time' for the photon.
For objects like us, which move only minimally in the spatial dimensions, goes almost every movement into the time.
This means that we are moving at almost the speed of light on the time axis.

And the faster we move in space, for example with a space ship, the slower we move in time.
If we were able to fly with the speed of light, time would stand still. If we were able to fly to Alpha Centauri like a photon, about 4.5 years would pass in the outer world. For us, there would be no time at all because we were standing still on the time axis.

But the real speed with which we move is always the speed of light.



( For me, it's perfectly fine if people are a little skeptical about the things that are told by scientists (the village elders, the shamans, the wise man of the tribe, whatever).

Otherwise we would still stare at the mountains on the horizon, and think that is the edge of the world that can not be overcome.)





Don't forget to look here.



Edited by JackDole - Saturday, 08.10.2016, 11:10
 
apenpaapDate: Saturday, 08.10.2016, 09:51 | Message # 820
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Quote JackDole ()
I did not know this was scientifically proven!
I do not believe in astrology.
But that stars have an influence on my life, I do not consider it to be more improbable than the quantum entanglement.


Well, it's practically impossible to prove a negative, so technically it's not scientifically proven that astrology is bogus. However, we can test its predictions and find that they don't come true more often than random chance indicates. Put another way, you can take any horoscope, switch around the predictions between signs, and you'll find people still report the prophecies mostly came true, even though they're now getting prophecies for the wrong sign.

Quote
Quote PlutonianEmpire ()
that Alf Cen cant have Gas giants like Avatar

Why can Alpha Centauri not have gas giants? (Of course there can be no Unobtanium. Therefore, it is called Unobtanium. If there was an element with the properties, it would not be a Unobtanium.)


Alpha Centauri can't have gas giants because we would have found them by now. Since Alpha Centauri is so nearby, we can place an upper limit on the mass of any undiscovered planets that could still be there just by the limits of our current methods. I'm not sure exactly where this limit lies, but it's below gas giant level.





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JackDoleDate: Saturday, 08.10.2016, 11:06 | Message # 821
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Quote apenpaap ()
Put another way, you can take any horoscope, switch around the predictions between signs, and you'll find people still report the prophecies mostly came true, even though they're now getting prophecies for the wrong sign.

This proves only that so far no one has succeeded in making exact predictions.
Or rather, if someone has made any exact predictions, he has kept them to himself, and they are not generally known.
But it does not prove that astrology is nonsense.
Although I personally think astrology is nonsense. But even I myself have occasionally been wrong. cool

Quote apenpaap ()
Alpha Centauri can't have gas giants because we would have found them by now.

Okay, I did not think of it. I think I can accept that.

However, I must confess that I am generally somewhat skeptical about our ability to discover exoplanets.
It is the talk of measured values which are so enormously small that, statistically speaking, they are almost not true.
But of course I can not really judge this. dry





Don't forget to look here.

 
steeljaw354Date: Saturday, 08.10.2016, 11:38 | Message # 822
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Watsisname, I mean if that moon would stay in the orbit our current moon is in and rotate once every 6 days, like the earth was never hit by the mars size object and captured this moon into the orbit we have currently.
 
HuesudoDate: Saturday, 08.10.2016, 13:21 | Message # 823
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Quote apenpaap ()
Alpha Centauri can't have gas giants because we would have found them by now.

Oh, I thought you meant that something impeded A Cen from having gas giants
 
PlutonianEmpireDate: Saturday, 08.10.2016, 18:49 | Message # 824
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Yeah, the current upper mass limit for worlds orbiting Alf Cen is approximately 10 Earth masses, based on RV measurements. smile




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WatsisnameDate: Saturday, 08.10.2016, 22:57 | Message # 825
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Quote JackDole ()
It is the talk of measured values which are so enormously small that, statistically speaking, they are almost not true.


Well, the the charge of the electron is 0.0000000000000000001602 Coulombs, but we can measure it and know it's true. It's mass is 0.0000000000000000000000000000009109 kilograms, but we can measure it and know it's true.

Measurement of small numbers is not in itself a problem at all. The problem is precision. To distinguish any number from zero, your measurement must be of sufficient precision such that the number itself is significant. A quantity might even be huge -- say 100 kilometers. But if your ability to measure distance is only precise to 1000km, then 100km is indistinguishable from zero.

If a planet causes its star to wobble by only 1 meter per second, then to discover it you must be precise to tenths of a meter per second. Which we can do! smile Similar idea for transit method. We must be able to measure changes in the brightness of the star to hundredths, thousandths, or even ten thousandths. Which we can do. Then, further confidence that this measurement is real -- that it really is a planet -- comes from repeated observation. A real planet must consistently produce the same result with each orbit.

Quote steeljaw354 ()
Watsisname, I mean if that moon would stay in the orbit our current moon is in and rotate once every 6 days, like the earth was never hit by the mars size object and captured this moon into the orbit we have currently.


Oh, I completely missed your second post -- sorry! Ok, so first off, it's pretty hard to know what Earth's rotation rate would be in this scenario.

Earth's current rotation rate slows down due to the tidal interaction. The rate of change of the rotation rate is proportional to the square of the Moon's mass (some really neat astrophysics behind this), so the 62% more massive moon would slow Earth's rotation rate about 2.6 times faster. Instead of losing about 1.7 milliseconds per century, we'd be losing 4.4 milliseconds per century.

However, this rate of change isn't constant and depends very sensitively on how far away the moon is. Since the real moon was formed from the impact and was originally much closer to Earth, there's a complex history of change in Earth's rotation rate. And the moon-forming impact itself surely changed Earth's rotation as well, which would not happen in this captured-moon scenario. So we can't really say what the length of day on Earth would be now -- we can only say how quickly it is changing.

What would the moon look like? It would be 62% bigger, and 2.6 times brighter when full. It would be a bit more impressive of a presence in the sky, but not a whole lot. Correction: it's 62% more massive, not 62% larger. It's actually smaller -- 79% the size of our Moon. It is 38% fainter when full. Less impressive in the sky, but it makes bigger tides. Neat.

It would be interesting if it has a 6 day rotation rate. People, or whatever other intelligent life exists in this world, would not only see different phases of the moon but also different faces.

Tidal evolution would also affect the moon's 6-day rotation rate. Using the formula for tidal locking timescale:



The moon would become tidally locked pretty quickly -- only about 10 million years.





 
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