Ask a physicist anything. (8)

[Wiccan_Child]

I've heard of particles moving faster then the speed of light. I read it is some school litterature in highschool. i cant remeber the name of the particle. I thought i might inform you of this!

No known particle travels faster than light, but such particles are called 'tachyons'.

 

[Naraoia]

(some physicist believe that, when a particle accelerates, its mass increases, which is one reason why it's impossible to hit lightspeed; I personally don't ascribe to that idea)

Maybe you answered this before, but what is your take on this? Increasing mass seemed like such a great reason why you can't reach light speed. What's wrong with it? Is it too intuitive to be true?

 

[Nabobalis]

Do you happen to use Bessel functions in your work?

 

[Zippy the Wonderslug]

If there was a massive earthquake or some type of incredible explosion that would send our planet's orbit, and we're talking just a very tiny and small fraction here, a little bit closer to the sun, how does Earth still avoid the sun's intense gravitational pull?

It would seem like this huge, continual force from the sun would start out extremely little but eventually this would begin to tug at us exponentially until we're spinning directly into it's path.

Am I making any sense to this question?

I know that our planet doesn't have a perfect orbit, but what keeps it all in check?

Thanks ahead!

 

[razeontherock]

Ok, I don't want to get too far into cosmology, but:

Weird Galaxy Glows Bright in Amazing Telescope Photo - Yahoo! News

I'm still struggling with this "expanding space" idea. From the link:

"These intriguing features, and the strong radio signals from Centaurus A, strongly suggest that the galaxy is the result of a violent galaxy merger. The dusty band is likely the remains of a spiral galaxy that is being ripped apart by the gravitational pull of a massive elliptical galaxy, ESO officials said."

Now if space itself is expanding, and this is a separate property from any actual motion of heavenly bodies -- don't all such theories predict that 2 galaxies couldn't possibly collide, ever? Yet we see evidence of exactly this happening ...

How do we explain that?

 

[NGC 6712]

Ok, I don't want to get too far into cosmology, but:

Weird Galaxy Glows Bright in Amazing Telescope Photo - Yahoo! News

I'm still struggling with this "expanding space" idea. From the link:

"These intriguing features, and the strong radio signals from Centaurus A, strongly suggest that the galaxy is the result of a violent galaxy merger. The dusty band is likely the remains of a spiral galaxy that is being ripped apart by the gravitational pull of a massive elliptical galaxy, ESO officials said."

Now if space itself is expanding, and this is a separate property from any actual motion of heavenly bodies -- don't all such theories predict that 2 galaxies couldn't possibly collide, ever? Yet we see evidence of exactly this happening ...

How do we explain that?

The expansion of spacetime on the local scale is negligible and local motions of objects overcome any such effect. It is only on the very large scales where the expansion manifests itself.

 

[razeontherock]

local motions of objects overcome any such effect.

That would be painfully obvious if our galaxy were being intruded upon by another ... Still, doesn't the expanding universe idea have the big bang at it's center? Why doesn't this phenomena falsify that?

 

[Wiccan_Child]

Ok, I don't want to get too far into cosmology, but:

Weird Galaxy Glows Bright in Amazing Telescope Photo - Yahoo! News

I'm still struggling with this "expanding space" idea. From the link:

"These intriguing features, and the strong radio signals from Centaurus A, strongly suggest that the galaxy is the result of a violent galaxy merger. The dusty band is likely the remains of a spiral galaxy that is being ripped apart by the gravitational pull of a massive elliptical galaxy, ESO officials said."

Now if space itself is expanding, and this is a separate property from any actual motion of heavenly bodies -- don't all such theories predict that 2 galaxies couldn't possibly collide, ever? Yet we see evidence of exactly this happening ...

How do we explain that?

The expansion of space accelerates galaxies away from each other, but there are more forces at work than just that. Electromagnetism, the weak nuclear force, and the strong nuclear force, are too weak to change the way galaxies move, but gravity, now that can be strong enough.

On average, galaxies move away from each other due to the Big Bang. Locally, gravity can be stronger than this 'Big Bang force' - that is, after all, how galaxies themselves stay together. So galaxies that are close together can exert gravity on each other that overrides the average moving-away effect, creating local structures like clusters and filaments.

Short answer: gravity .

That would be painfully obvious if our galaxy were being intruded upon by another ...

Actually it is - or will be, in a few billion years. The Andromeda galaxy is hurtling towards us. Run!

Still, doesn't the expanding universe idea have the big bang at it's center? Why doesn't this phenomena falsify that?

That's not quite how it works. The Big Bang theory says that the universe has been expanding for 13.5 billion years from a tiny, hot, dense state. The Big Bang itself is this ongoing expansion, it's not a thing that has a location, nor does this expansion have a centre somewhere in the universe we can send a spaceship to.

Everything expands away from everything else. We don't see the Earth moving away from us, but we see distant galaxies accelerating away, and further ones accelerating away even faster. However, this is what you'd see no matter where you are in the universe. There's no central point, as every point is moving away from every other point.

 

[NGC 6712]

That would be painfully obvious if our galaxy were being intruded upon by another ... Still, doesn't the expanding universe idea have the big bang at it's center? Why doesn't this phenomena falsify that?

Actually two galaxies colliding results in on average about zero collisions between stars. What does happen is the gas present in each system becomes turbulent and this induces a large star formation event.

No centre for the Big Bang. Spacetime expansion is at all places at once.

 

[David Jerome]

What is the second fastest (naturally) moving particle?

 

[razeontherock]

So galaxies that are close together can exert gravity on each other that overrides the average moving-away effect,

Everything expands away from everything else. We don't see the Earth moving away from us, but we see distant galaxies accelerating away, and further ones accelerating away even faster. However, this is what you'd see no matter where you are in the universe. There's no central point, as every point is moving away from every other point.

It would be interesting to model what sort of "zone" needs to exist, for galaxies to be close enough to overcome expansion, but far enough away not to crash into each other for however many zillions of years, such that we can witness it now

 

[razeontherock]

What is the second fastest (naturally) moving particle?

Photons? (That's why the Klingons do so well)

 

[selfinflikted]

ed.

 

[Wiccan_Child]

It would be interesting to model what sort of "zone" needs to exist, for galaxies to be close enough to overcome expansion, but far enough away not to crash into each other for however many zillions of years, such that we can witness it now

It would, but the calculation is intractable.

If we take a purely mathematical approach and try to model how three (or more) bodies of arbitrary mass, position, and momenta, would move at any given point... it turns out it's impossible. You simply cannot run through the algebra and say, "OK, if they had these initial conditions at t = 0, they would have these conditions at t = t" - c'est impossiblé.

Instead, we have to use statistical approximation using iterations and computer simulations.

So, trying to model this galactic 'boundary' with so many variables would be even more impossible (if that makes any sense ). You'd have to factor in your own galaxy's mass, the mass of the other galaxy, its position and velocity, etc, and all the other factors like the other galaxies in the local area, and you have to take into account the fact that galaxies aren't nice, discrete objects, but huge conglomerates of stars (the dynamics of stars within a galaxy is quite fascinating in itself).

And let's not even get started on dark matter...

 

[Wiccan_Child]

What is the second fastest (naturally) moving particle?

Well, apart from c, there's no hard limit on how fast a particle can go, so any particle can go at any speed. That said, you tend to find neutrinos moving at almost c, so I'd say them.

 

[razeontherock]

Well, apart from c, there's no hard limit on how fast a particle can go, so any particle can go at any speed. That said, you tend to find neutrinos moving at almost c, so I'd say them.

Wait, I thought tachyons could beat light, which would make light the second fastest thing?

 

[razeontherock]

If we take a purely mathematical approach and try to model how three (or more) bodies of arbitrary mass, position, and momenta, would move at any given point... it turns out it's impossible. You simply cannot run through the algebra and say, "OK, if they had these initial conditions at t = 0, they would have these conditions at t = t" - c'est impossiblé.

So what we can know has hard limits? Ok ...

 

[Naraoia]

Wait, I thought tachyons could beat light, which would make light the second fastest thing?

That would be... the infinity-eth fastest, no? Tachyons, if they exist, can move at any speed above c.

... Sorry, just had to.

 

[razeontherock]

Tachyons, if they exist, can move at any speed above c.

Well, that's just tacky, showing off like that

 

[Wiccan_Child]

Wait, I thought tachyons could beat light, which would make light the second fastest thing?

Tachyons aren't an actual type of particle, though; they're the name given to any particle that goes faster than light. 'Tachyon' is the same kind of word as 'sub-luminal' - it's not an actual particle itself.