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N0B0DY
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27 Jun 2017 02:59

Thank you all for your very informative and enlightening replies! So I presume the distance of Betelguese will be corrected for the next version :)
 
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Starlight Glimmer
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30 Jun 2017 11:00

What if a new comet was discovered, and it was going to impact mars? 
 
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DoctorOfSpace
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30 Jun 2017 11:56

It would impact Mars and a lot of astronomers would have a fun time
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Spacer
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30 Jun 2017 11:57

DoctorOfSpace wrote:
It would impact Mars and a lot of astronomers would have a fun time

but not our rovers i guess  :)
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Mr. Missed Her
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01 Jul 2017 05:37

Spacer wrote:
DoctorOfSpace wrote:
It would impact Mars and a lot of astronomers would have a fun time

but not our rovers i guess  :)

Well, it most likely wouldn't destroy our rovers directly, but the impact would be bad news for our rovers. The impact probably would kick up a lot of martian dust, resulting in a long sandstorm that would block out the Sun and finally kill the long-lived Opportunity. But wait! Curiosity doesn't have solar panels, it's nuclear powered! And radio signals could probably penetrate the dust, so Curiosity should still be fully functional.
 
Mr. Missed Her
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01 Jul 2017 05:41

Also, I heard Jupiter emits a wide range of radio waves very intensely in some directions. Is it possible for a gas giant to emit radio waves in a similar manner, but in a very narrow frequency range?
 
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06 Jul 2017 02:19

Q1: Is the wormhole in SpaceEngine using Ellis-wormhole metric (i.e. Image)? 
Q2: Is the warp drive using Alcubierre metric? 

What I mean by using is that the lensing effect of curved space-time showing in the game.
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06 Jul 2017 14:28

Assuming there were to be a multiverse somewhere out there, what's the likelihood it could be of a fractal of some sort, or have a fractal "appearance?"
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JCandeias
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12 Jul 2017 07:00

This looks like the least wrong place to put this, so here goes.

Someone made a theoretical planetary system that maximizes the number of planets in the Habitable Zone. The result? 416 planets. Yes, really. Check it out: http://nautil.us/blog/i-built-a-stable- ... ign=buffer

Someone needs to make an addon for SE with this crazyness (or any of the other slightly less crazy variations he started with)... :)
 
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12 Jul 2017 10:45

Here is one question. I don't know how many of you are going to agree with this statement, but:
What if gravity does not exist? Maybe there's Electromagnetism instead of gravity. I am trying to learn as much as possible about everything, including electromagnetic forces. Say what's your opinion. :)
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Watsisname
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12 Jul 2017 22:29

You can try to treat gravitation as an aspect of electromagnetism, but that would just complicate electromagnetism, specifically by adding something which is indistinguishable from gravitation.  Let's see why they must be different things by checking some observations. :)

We'll start out simply.  Perhaps the simplest observation we can make is that certain materials can become "charged".  For example, we can rub a plastic rod with some wool, and suddenly it gains this magical ability to attract things, like small bits of paper.

We can also see that this charge can be transferred.  Touch the rod to a free-hanging metal sphere, and now the sphere is charged and exhibits the same behavior.  Now do this exact same process for another metal sphere, and bring the two close together without touching.  They repel!  That's interesting.  Apparently this "charge" stuff doesn't like itself.

Ok, now let's do something a little different.  We'll take another metal sphere, and while holding the charged rod close to (but not touching) it, touch the sphere with a wire connected to ground.  Then remove the wire, and then the rod.  The sphere is now charged, even though we never touched it with something charged!  Furthermore, this sphere will also attract the other two spheres we prepared earlier, and attract small bits of paper.


What this shows is that there are two types of charge.  Two objects with the same charge repel, and the "opposite" charges attract.  This is well known to us of course, but it's instructive to think about how to show it, and then what it implies:

If we think gravitation is an aspect of electromagnetism, then it should seem odd that masses always attract, while charges can attract or repel.  It should seem odd that we can give an object either charge and it always has the same attraction to Earth.  

Well, maybe "mass" is just another kind of charge, which attracts all the other kinds of charge?  Sure, you could try to go with that.  But like I claimed above, that's equivalent to adding something equivalent to gravitation to electricity at this point.

Let's investigate a little more deeply, and bring in magnetism:


We observe that a charged object moving through a magnetic field experiences a Lorentz force. However, this is not true for massive but uncharged objects, or for objects (charged or otherwise) moving through a gravitational field.  This really indicates that gravitation and electromagnetism must be different kinds of interactions associated with different kinds of physical properties.

Perhaps now you are thinking,
"But no Lorentz force appears within a purely electric field.  Maybe a gravitational field is just an electric field?"  

But that still doesn't work, because of how electricity and magnetism are related:

A stationary charge produces an electric field.  Electric currents (moving charges) also create magnetic field.  But by relativity, an observer moving alongside a moving charge will say the charge is stationary and thus there is no magnetic field, while different observer may say that it is moving and is producing a magnetic field.  So electricity and magnetism are related by relativity, and together form the electromagnetic field.

This works differently for gravitation.  A gravitational field doesn't split up into different types depending on your speed relative to the source.  If gravitation is electric field in the rest frame and magnetic field in the moving frame, then you should still be able to demonstrate Lorentz forces on uncharged objects.


We'll go one last step and examine electromagnetic vs. gravitational waves.  

Moving charge produces a magnetic field, and changing magnetic fields produce electric fields, and vice versa.  If a charge should move in a particular way (in the technical jargon, a "changing dipole moment"), then these changing electric and magnetic fields propagate at the speed of light.  That is, they make an electromagnetic wave.  An example of a changing dipole moment is two particles oscillating back and forth, like two masses on a spring.

A similar thing happens in gravitation, but the nature of the source required, and the behavior of the waves, is different. Instead of requiring a changing dipole moment, it requires a changing quadrupole moment.  An example of this kind of motion is two objects orbiting each other, or a mountain on the equator of a rapidly spinning ball.  This emits gravitational waves, which also propagate with the speed of light, but instead of affecting charges, they stretch and squeeze space.



In summary, I hope this was a good introduction or review of some of the physics of electromagnetism, and perhaps helps convince you that these really are two very different kinds of interactions. :)  Finally, not only do they have different sources and behaviors, they have *very* different strengths.  The electromagnetic interaction is about 1036 times stronger than gravity!
 
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Marko S.
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13 Jul 2017 02:28

The explanation with metar rods and spheres that attract and repel can be dismissed. That's school explanation. You explained well everything.
But, if magnetic forces are 1036stronger than gravity, does that mean that we can create some sort of anti-gravity craft? Nikola Tesla was working on that, and he completed the patents! But sadly, everything was taken from him when he died. I just feel sorry for him. There's a lot of thing that would be possible if only he got the funding from non-greedy people. This is off-topic, but I want to mention this.  And thanks for your time trying to explain the gravity! :) Even if time doesn't exist. xD
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Watsisname
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13 Jul 2017 13:27

Marko S. wrote:
Source of the post But, if magnetic forces are 1036stronger than gravity, does that mean that we can create some sort of anti-gravity craft?

It is easy to use magnetic forces to levitate things, but the difficult part is keeping stability, or levitating more than a very small distance (the magnetic force drops as 1/r^3).  You can stabilize a paramagnetic levitator with spin, or you can use diamagnetic materials.  A fun demonstration of totally stable magnetic levitation is through the Meissner effect with superconductivity.  We also use magnetic levitation for high speed trains. 

If one desires a more general kind of flying craft that balances the gravitational force at any desired altitude?  That's more difficult to imagine from the physics.  Levitation works not by producing opposing gravitational forces, but by producing opposing magnetic forces.  There isn't a convenient magnetic field around the Earth to use for this -- Earth's field is very weak and oriented in different directions at different latitudes.

Let's do the math.  Magnetic pressure is [math]

Pressure is force per area, and we want the magnetic force produced by opposing Earth's magnetic field to balance the gravitational force on us and our craft which is mg.

The Earth's magnetic field at the surface ranges from 25 to 65 microtesla.  Let's pretend it is 65 microtesla everywhere and oriented vertically.  What surface area on an opposing magnet would you need in order to levitate a 60kg person against this field?

[math] = 350000 m2 = 35 hectares.

That's more than 6 times the area under the great pyramid of Giza!  Pretty impractical, not to mention that this size of magnet on your levitating craft would add to the weight which will add to the size requirement.  In other words, this will never work.

In order to levitate a 60kg human on something about 1 square meter in size, the field strength must be about 40 millitesla, or about 1000 times stronger.  We can achieve this very easily with modern magnetic materials or electromagnets, but of course, it requires having the same magnetic base on the ground below you everywhere you go to produce the opposing field, and by Earnshaw's Theorem, you have to use something more complex than just static paramagnets to maintain stability.

So perhaps Tesla himself figured out a way to build a stable magnetic levitator back in his day, but by the physics, it cannot be a thing that acts like a flying car and solves all our transportation problems.  Sadly. =(
 
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Starlight Glimmer
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13 Jul 2017 14:29

What if Earth had 2 moons? 

Like half moon sized moons, 1 orbiting half the distance of Earth and the moon, and the other orbiting where the moon is now?
 
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Marko S.
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13 Jul 2017 16:30

Starlight Glimmer wrote:
What if Earth had 2 moons? 

Like half moon sized moons, 1 orbiting half the distance of Earth and the moon, and the other orbiting where the moon is now?

Well, first noticable thing would be that, we would see 2 moons in the sky, logically. :)
Second is that the waves system would be different. If the closer moon, let's name it Moon A, and the other Moon B, is curently seen on the sky, the sea waves would be higher than if the Moon B would be curently on the sky. But, what if both Moons are on the same side? Would the waves be higher? Probably. But it depends on the positions of the Moons.
Third thing is the Eclipse. We would not have the Eclipse what we have now. If the Moon A is blocking the Sun, it would be the same as the Eclipse we have now. If I'm not mistaken, then it would cover the whole Sun. That's because the Moon A (closer one) is double the size of the Original Moon and at the same time it is closer twice than it should. But, the story is different for the Moon B. You can already guess that there wouldn't be the Total Eclipse.
That's my explanation and if you have another related question, ask. :D And if I missed something, there's always Watsisname that can explain everything. :) :)
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