Ask a Physicist

[Lyinginbedmon]

With the number of physicists around here and the seeming eager and readyness they have to answer what I'm sure are simple questions or fun challenges to explain, I figure we might as well have a place for them to readily seek out said challenges and questions and further enlighten the LRRum populace.

Guess I'll submist the first question then:

The sun is a massive gravity-generating object at the centre of the solar system, around it are the planets on which it continually pulls. As you get closer to the sun, it's gravitational pull on you gets stronger (So if you get close enough you pretty much can't escape).

Why then is it that the orbits of some planetoids in our solar system (Mercurcy and Pluto for example) pass close behind the sun but come right back out to fly much further away?

And why is it that in 3D space with gravity operating on a 3D level the planets all line up on relatively the same 2D plane?

[Alja-Markir]

I'm not a physicist per se, but I have answers for you.

Answer 1 - Those objects with extremely elliptical orbits, such as comets, operate under all the normal rules of gravity. When a comet approaches the sun, the sun exerts more pull on the comet. The comet accelerates to very high speeds, while simultaneously getting closer and closer to the sun. Once it reaches a certain point, the gravitational pull is too much and the comet radically shifts in direction and is slingshotted around the sun.

As the comet then flies away from the sun, it loses speed because the sun's gravity is now pulling it backwards. This slows the comet down considerably, but the comet has so much inertia that it is able to pretty much just barely break free. As it gets farther and farther away, it slows to a crawl. Furthermore, as it gets further and further away, the sun's gravitational effect on the comet drops as well.

This is why comets take a very long time to finally turn around again. The comet never actually escapes the sun's pull, though, which is why it eventually reverses course. And then the cycle begins all over again.

Answer 2 - The planets all fall within relatively the same orbital plane because of the nature of the formation of the solar system. Imagine, if you will, a big mass of matter and energy, a cloud of sorts, but one which is spinning itself into a disc. That's vaguely what the solar system looked like rather a long time ago. Over time the matter slowly took shape and organized itself, forming the planets as well as the sun, all within the same plane of rotation.

It's kind of like a centrifuge. If you stick a bunch of liquids of different densities together in a vial, then stick that vial into a centrifuge, the liquids will separate out based on density. Needless to say, the properties of the formation of a solar system are indescribably more complex, but the analogy is sound.

~Alja~

[Keab42]

Alja's pretty much spot on. His second answer is the current best guess for solar system formation, it's something that we're still investigating.

[epocalypse]

How likely is it to see a cohesive unified theory in our life time, and what are the largest current obstacles (outside of time traveling particles) standing in the way?

[BritchesStitches]

Well... I don't think we want to get into a discussion as to whether String Theory is valid (or if it's even a real theory)... but that's somewhat cohesive and unified.

As for what's standing in the way... Gravity?

[Keab42]

Well the LHC and a couple of planned experiments that will use greater energies are hoping to provide data that will help us get closer to a GUT.

Gravity is the biggest problem, it acts over such vast distances and we have no idea how the force itself is transmitted, we've got theories, but no evidence.

But there are other things that stand in our way as well. The theory is that at high energies, such as those found in the moments after the big bang that the forces unify, hence the experiments such as the LHC.

[Lyinginbedmon]

How does the LHC intend to accurately duplicate the events of the Big Bang when it occurs in a pre-existing universe on a planet with substantial gravity?

[epocalypse]

...

shut up, they might hear you!!

[BritchesStitches]

How does the LHC intend to accurately duplicate the events of the Big Bang when it occurs in a pre-existing universe on a planet with substantial gravity?

The intent isn't to accurately duplicate the Big Bang, but to observe particles when put under similar, high energy conditions (as Keab42 said). It's an on-going process.

[Lord Chrusher]

The LHC was never meant to recreate the big bang; it was intended to recreate some of the conditions that existed early in the universe.

[steelfox]

I heard about some swirl thing in the sky near the LHC.

Was that real, if so what the hell is it?

[Master Gunner]

There was a missile that malfunctioned and made a big swirl-type thing in Norway or something. Haven't heard of anything anywhere near the LHC though.

[Lord Chrusher]

A few weeks ago some weird swirly things were seen over Norway and Russia due to some Russian rocket tests. I have not head of any connections with the LHC.

[Master Gunner]

Obviously, the Higgs Boson did it.

[iamafish]

the higgs boson came back from the future to do it

[Snowfire]

No. That would be the neutrino good sir. Or the tachyon.

[Lord Chrusher]

I am going to take a stab at answering Lyinginbedmon's first question. But I am going to ask then answer a different question first.

Why do objects orbit a star rather than fall in?

If the object was initially at rest with respect to the star then it would fall right in. However in general an object will have some speed in a direction perpendicular to a line that runs through the star and the object. Gravity tries to pull the object towards the star but since it is also moving in a transverse direction rather than moving directly towards the star it moves towards the star at an angle. This process repeats its self, causing the path of the object to curve. If the object was originally moving in just the right direction and at just the right speed the orbit will be circular. If the object is moving slower, the object will move closer to the star, picking up speed as it gets closer. However it never moves directly towards the star, always to the side of the star. Eventually the object is moving perpendicular to the star and starts to move away from the star and starts to slow. The object moves out to where it previously was and turns back, completing an orbit. If the object was initially moving faster than it would in a circular orbit it move farther away from the star before moving back towards the star and pass through its initial location. In any case the object tries to fall towards the star, but always misses it causing the object to move in an elliptical orbit.

[Re'ozul]

If the universe is expanding, does it have something that could be classified as an edge?
I have trouble imagining this all the time.
How do you calculate the "size" of the universe without coming to the ballooon analogy?

[Arius]

How do you calculate the "size" of the universe without coming to the ballooon analogy?

It's like a soufflé?

[Lyinginbedmon]

If the universe is expanding, does it have something that could be classified as an edge?
I have trouble imagining this all the time.
How do you calculate the "size" of the universe without coming to the ballooon analogy?

The question I think your tiptoeing around there is

"What's outside of the universe?"

The simple answer there is, we don't know. Heck we can't even see one side of the universe much less anything beyond it.
The less simple answer is, it could be just about anything.
The least simple answer is, absolutely nothing, not even space. That's the least simple because the human brain has trouble with the concept of absolute nothingness, beneath even the low levels of existence in the empty vacuum of space.

[theDreamer]

Lyinginbedmon.

Universe means, literally, "everything that exists."

There is nothing outside the universe.

The universe is infinitely large.

The stuff in the universe are just expanding ever outward into the nothingness that is more universe.

Of course, I could be wrong, but then the English language and Bill Bryson have failed me.

[Snowfire]

Ah. Not technically true. There is the possibility that this entire universe is just the intersection of two four dimensional objects. Which means this entire universe could just be an experiment in a lab somewhere. Of course, that begs the question of where that lab is...but that's too darned confusing to go into at this sort of time.

I'll update this to explain later.

[Arius]

Wait, what if there were multiple bangs?

Then sooner or later, the stuff from our bang will start crashing into the stuff from the other bangs. At least within the bang, everything is moving away from each other. In a multibang universe, galaxies are fucked. The cosmos would crash into each other and then a big crunch would no longer be the worst possible outcome, arguably of course, since the big crunch would mean an end to the galaxies. But what is worse? An absence of existence or a wasted existence?

Also, heh... Multibang.

[DmitriW]

Wait, what if there were multiple bangs?

Then sooner or later, the stuff from our bang will start crashing into the stuff from the other bangs. At least within the bang, everything is moving away from each other. In a multibang universe, galaxies are fucked. The cosmos would crash into each other and then a big crunch would no longer be the worst possible outcome, arguably of course, since the big crunch would mean an end to the galaxies. But what is worse? An absence of existence or a wasted existence?

Also, heh... Multibang.

I can only assume that the collision between "bangs" would be scarcely any worse than a collision between galaxies. Things would get shaken up a bit, but outright destruction would be more-or-less unheard of.

Also, if my totally-uneducated theory about what the Big Bang actually was is even scientifically possible, let alone accurate, than the odds of a multibang universe are more-or-less nil.

[BritchesStitches]

Yeah, the question of "what's outside the universe" is along the same lines of "what happened before the big bang?" there was no space nor time before the big bang. And yeah, the universe is expanding in the sense that things are getting bigger/further apart.

Also, I'm not too sure about this, but I believe a current theory is that there was a small bang followed by a big bang... that's kind of a multibang.