“I assume that you mean that your personal “‘Hubble Expansion’ theory” has holes in it.”
Hmmm …
The Hubble Expansion
“During the 1920’s and 30’s, Edwin Hubble discovered that the Universe is expanding, with galaxies moving away from each other at a velocity given by an expression known as Hubble’s Law: v = H*r. Here v represent’s the galaxy’s recessional velocity, r is its distance away from Earth, and H is a constant of proportionality called Hubble’s constant.”
“The exact value of the Hubble constant is somewhat uncertain, but is generally believed to be between 50 and 100 kilometers per second for every megaparsec in distance, km/sec/Mpc. (A megaparsec is given by 1 Mpc = 3 x 10^6 light-years). This means that a galaxy 1 megaparsec away will be moving away from us at a speed of between 50 and 100 km/sec, while another galaxy 100 megaparsecs away will be receding at 100 times this speed. So essentially, the Hubble constant sets the rate at which the Universe is expanding.”
Let’s see, according to this Hubble expansion description and formula, a galaxy is either moving away or receding from us … I can think of a situation where an object is either moving away or receding from us that could possibly impact on us? Jeez … it looks like a pretty simple formula …
There are actually other galaxies colliding with the Milky Way in addition to the Magellanic Clouds, but I think they’ve only been discovered recently. At least one of them is so close to us that it’s closer than some of the stars in the Milky Way and it’s pretty hard to see because it blends in so well with the stars in the Milky Way.
That quote isn’t saying that all the supernovae are old stars that are suddenly blowing up because of the galactic collision. These are actually relatively young stars whose formation was triggered by the density waves from the collision, and they’re so massive that they’re going supernova at a very early age.
Here’s a simple formula, too: a=-GM/r^2. According to this formula, I should be plummeting toward the center of the Earth, accelerating at the rate a!
But yet I’m not! What’s going on? Hang on, what’s this thing underneath me? It appears to be a “chair” and the chair is exerting a force on me that prevents me from accelerating as that formula predicts.
Is the formula full of holes? Completely wrong? No, it simply describes the motion of an object affected by gravity but no other forces. Just because a formula exists doesn’t mean it always applies.
In the absence of other effects, galaxies follow the Hubble flow. However, they are not bolted onto a particular point in space. If the gravity between two galaxies is strong enough, space still expands between them, but they travel toward each otherthrough space faster than the space can expand and carry them apart. Remeber, v=H*r, but F=GMm/r^2, so for objects that are close to each other (like nearby galaxies or, oh, say, you and the Earth) the Hubble flow is a small effect, but gravity is very strong.
Imagine two railroad cars moving slowly away from each other. If you are on one car, and your friend is on another, you can run along the cars so that, despite the fact that the cars are moving apart, you and your friend are moving toward each other.
(By the way, if you give a direct quote like you did above, it’s nice if you mention where it comes from.)
Indeed, that’s incorrect. Expanding a bit on what Bob said: The “ripple” is a density wave through the interstellar medium, which can cause new star formation. The rule with stars is that the more massive the star, the faster it burns through its nuclear fuel, and the quicker it reaches the supernova stage. Massive, hot, blue stars don’t live long, so star-formation regions are full of bright blue stars and supernovae (and supernovae can cause density waves of their own which cause even more star formation).
Eventually, the blue stars all go off in SN explosions, so in older regions where star formation has been absent for a time, we find smaller, more pedestrian stars like our Sun and red dwarfs, which live for much much longer. A density wave passing through the interstellar medium would effect a star’s heliosphere (the hollow in the interstellar medium carved out the solar wind) but it won’t trigger any star deaths. Stars only die when they run out of fuel. In the case of smaller stars mean that they have to run out of hydrogen. For smaller stars, death is much less spectacular: no galactic-scale explosion, just bloating up into red dwarfs, then slow shrinking and cooling.
Sorry if that was long and pedantic, but I’m not TAing this year, and I gotta get it out of my system.
Well, geez, I’m not real good at celestial mechanics, but the formula F=GMm/r^2 looks something like Keppler’s law. Shouldn’t we be able to calculate then, for two galaxies 300 Mpc distant, for example, the two galaxies net recessional velocity if the gravitational effects are, as you say “very strong”, relative to the Hubble expansion, v=H*r ? I’d really like to see a calculation, with real numbers, that shows the net recessional velocity between two galaxies? Even better, the calculation between us and Andromeda would be kewl! Would answer the question I think?
Podkayne answered part of my original question, which included what exactly IS expanding. At first I thought they meant each galaxy is flying away from each other, but then I read about our Local Group, that it stayed together, so I thought they must mean GROUPS of galaxies expand from each other, each one staying together as a group. Now this concept of Podkayne is a new idea to me, that space everywhere, with everything in it, is expanding, not just the space among very large groups of galaxies. But as he points out, the attraction of galaxies in a group for each other locally overwhelms the lesser force of the expansion of the space that is expanding everywhere! Now I’m wondering if the concept SPACE includes the atmosphere of earth, or better yet all that space in the atom! If that huge football field of space in each atom between the electrons and the nucleus as baseballs is not expanding at the Hubble rate, then what exactly isolates that space, which I will call Teensy Space or Microspace from the Macrospace among the planets, stars, and galaxies? If atomic space is expanding, then are the attractive forces of the teensy little nuclei and electrons in it stronger than the Hubbly expanding Microspace, thus keeping things together?
We honestly don’t know if the space within each atom is expanding, because that would take a theory of quantum gravity to describe. However, if it is, then it’s a miniscule rate. Assuming a Hubble constant of 65 km/s/Mpc, and an atomic radius of 1 Angstrom, we get that the space within the atom is expanding at a rate of 2.1*10[sup]-28[/sup] m/s. The electric attraction between the proton and electron is easily able to overwhelm that.
In all honesty, I must admit that I what I posted might not be totally correct. For one thing, it’s hard to boil down physics to everyday language sometimes, and for another, I don’t really know all the physics that goes into this, since general relativity really isn’t my forte.
Space expanding everywhere isn’t really right. Remember that massive objects affect spacetime; they are not passive travelers through it! So gravitational attraction between two bodies does (if I understand my reading correctly) actually prevent the expansion of spacetime over small distances. So the galaxy and the solar system (and the atoms in them) don’t expand.
I think (and I hope that someone who has a deeper understanding of the subject can help me out if I’m wrong) that the train car analogy I used before is part of the picture, but not the whole deal.
DeutschFox: If you can believe it, I had a whole calculation all typed out for you when Netscape crashed and died! I’ll redo it (in a text editor this time!) soon, but I must be off for now–I have a Halloween party to go to.
Just in case anyone savvy is reading, and before I redo the whole damn thing, does anyone know if it’s fair to say, in a very simplistic way, that if the Hubble velocity (v=Hd) is greater than the escape velocity, a gravitationally bound system will be unbound? Or is that completely wrong according to GR??? Thanks for you help!
Einstein did not disagree with the concept of an expanding universe.
Einstein wasn’t right about any major scientific isssue after 1915? Maybe it’s all in your definition of “major”, but I think the only way you can say that is if NO ONE else has been either.
And GMm/r^2 is not Keppler’s law.
The recent find actually has another galaxy currently colliding with the Milky Way, on the other side of the galaxy.
Geez, I can’t even spell Kepler correctly. And your right about the formula …
"In his law of universal gravitation, Newton states that two particles having masses m1 and m2 and separated by a distance r are attracted to each other with equal and opposite forces directed along the line joining the particles. The common magnitude F of the two forces is
F = G x (m1 x m2 / r^2)
where G is an universal constant, called the constant of gravitation, and has the value 3.439x10-8 lb-ft2/slug2 in U.S. units and 6.673x10-11 N-m2/kg2 in SI units."
Can it still be used to help calculate, with Hubble’s formula, the net recessional velocity of two galaxies or is that already considered in the Hubble constant?
The concepts I stated on Einstein were in, I believe, Time magazine addressing the most important people of the century or millennium? I know scientists will scoff at this kind of review, but then who does this Cecil work for? I will get the article for you to review …
In 1916, Albert Einstein announced his general theory of relativity and the following year produced his model of space based on that theory. Einstein argued that the universe was immobile, but Dutch astronomer Willem de Sitter calculated Einstein’s equation and proved that the universe was actually expanding. In 1922, Russian physicist Alexander Friedmann used Einstein’s equations to prove that the universe could either shrink or expand.
Hubble’s rule of an expanding universe
During the uncertainties of the era, Hubble was able to observe galaxies at distances up to 7 million light years away. By doing so he was able to come up with Hubble’s Law, which said that the further galaxies were away from earth the faster they moved away from our planet. Hubble’s rule proved the universe was expanding like a big balloon. In 1930, Einstein visited Wilson Observatory and viewed photos of galaxies taken by Hubble. After seeing the photographs, Einstein gave up his theory of an immobile universe for all time. The orbiting space telescope observing the universe is named after Hubble."
RM … is this correctly ??? or do you know something the general scientific community doesn’t know …
I’ll check. But for starters, I think that general relativity was published in 1915, not 1916. That quote doesn’t seem to be from the Time magazine century article.
1)Several times it was mentioned above that there had already been detected another galaxy now colliding with ours. What is its name? Also, 2) Is it really certain that the Maffei 1 and Maffei 2 Galaxies are NOT part of our Local Group? I used to read that they were and that Maffei 1 was a huge elliptical that would be reddish in color and the size of the moon if we could see it, but we can’t because it is through the galactic plane on the other side. I’m still aesthetically contemplating how space is expanding like clear jello, possibly even at the level of the space between the electrons and the nucleus, and the Even Teensier Space in among the protons and neutrons inside the nucleus. Add to this possibility the fact that just after the Big Bang the proton and neutron particles evidently didn’t exist, there was only gluons and quarks that then associated when things got cooler into little nuclei and electrons then came along somehow and we started to get atoms per se. Evidently the space within the atoms-to-be was always already there expanding but at a small enough rate to allow particle association.
Not only do I not know the name of the galaxy colliding with the Milky Way, it probably doesn’t even have a name. Most likely, it just has some dry number based on what observatory discovered it and how many similar objects that observatoy has discovered before.
RM … I’m sorry, this statement was not from a Time, Life, or People type magazine. I tried to find what a reporter might see in order to write an article on these subjects first …
Secondly, the concept of atomic level space expansion is way above my head … but …
I am still very interest in the apparent “fact” that galaxies are colliding. Is this consistent with the Hubble expansion? Secondly, I’m really not clear if the Hubble constant doesn’t already include the effects of gravitational attraction? If not, is it appropriate to combine gravitational effects such as Newton’s with the Hubble expansion formula? … and will this suggest that galaxies can collide per Hubble as modified …
or does the Hubble expansion model actually have holes in it, as I asked earlier. This is what I based my statement on, that specifically, “galaxies”, not local groups, clusters, etc., could not collide as the Hubble expansion seems to suggest. If galaxies can’t collide per Hubble, then they can’t, period … local groups or clusters or not! I had to ask for some vaseline. Now I am being told that the Hubble expansion does NOT exclude galaxies colliding … I really can’t see that, in anyway shape or form, in the Hubble expansion model. It could be that I am just too dense to understand, which is a real probability! … Thanks
An analogy to the expansion with colliding galaxies might be like hmmmm franchise expansion, yeh that’s it…fast food franchises aren’t limited to the USA, they’re expanding all over the world. They can still collide (be built in the sam e place), in fact, I know an intersection where there are thirty of them. See, if you build them fast enough, they can still collide.
Same with gravity. It’s acceleration overcomes the expansion as long as the galaxies are close enough.
