Missing mass in the universe? Is there a flaw in my reasoning?

Question

The outer galaxies are expanding at a rate close (some say more) to the speed of light.Thus the mass of these galaxies should also be close to infinty?
If you reason that the galaxies are not expanding but that only the space between the galaxies is increasing, I want to ask this question: " The space between the Earth and the Moon does not increase, nor the space between the Earth and the sun nor the space between the Sun and Alfa Centauri. So how does space carefully mannage to insert itself only in the space between galaxies?.

Answer 1

The expansion of the universe acts in the following way: as you go farther away from any point, you will move away faster from that point. For a distance of 1 mega-parsec, the speed is about 70 km/sec. Now, Alpha Centauri is about one and ahalf parsecs away, so the rate it would be moving away from us due to the universal expansion is only about .0001 km/sec, or a few inches per second. This is too small to be detected by any instruments we have and is way smaller than the orbital speed of that star around our galaxy. For the sun, we divide even this small speed by a factor of about 300,000. The orbital speeds of the planets and the reaction speeds of the sun are far, far below this amount.

In other words, the universal expansion is only detectable when the separation between objects is comparable to distances between galaxies. For anything closer (and even closer galaxies) the 'peculiar' motions of orbits, etc outweigh the velocities of expansion.

As for the galaxies that are quite distant from us moving at close to the speed of light, there is no measurable effect from the increase of mass from this velocity (unlike the observable ones for subatomic particles moving at those speeds) since no force produced close to us affects those galaxies in time for us to observe the effect.

Answer 2

Good questions. First, it is not necessarily true that galaxies are moving at the speed of light. They may be moving more slowly in their localities, but the expansion of space makes it seem like they are moving faster (even beyond the speed of light) relative to us. The first link I provide below will explain that it is a matter of defining distance and time to arrive at the true speed and its relation to Special Relativity.

As for the observation that inflation seems not to have an effect on the earth-moon system, there are a couple reasons for this. First, most of the expansion in the universe happened very early in its history, long before our solar system came into existance. The "Inflationary Epoch" in which most of the expansion occured happened in a blink of an eye, even before atoms had a chance to form out of the quark-gluon plasma.

This initial expansion phase did not result in a smooth distribution of matter. The universe was "clumpy", with regions of relatively dense matter and vast space inbetween. These clumps later evolved into the galaxies we see today. The clumps have long been moving apart from each other, even as the initial expansion phase slowed down, which accounts for the red shift we see for faraway galaxies.

Cosmic expansion is still going on, but at a much lower rate than the first spurt. In fact, most cosmologists believe it is accelerating again. But the effects of this inflation are no where near as strong as the force of gravity that is holding our local matter clumps (galaxies and star systems) together. It has been calculated that inflation accounts for just one septillionth of the size of earth's orbit over the age of the solar system.

It will never be strong enough to rip our galaxy or solar system apart, but the faraway galaxies which have only a very tenuous connection to us will fade away.

Answer 3

The expansion of space is small compared to orbital and proper motion on scales up to galaxy clusters. The Hubble constant of 71 km/s/Mpc (kilometers per second per mega-parsec) amounts to a mere 22 mm/sec (78 meters/hour) per light year, or less than a third of a kilometer per hour over the distance between here and Alpha Centauri. This is minuscule compared to the velocity of the star.

Answer 4

I think it's gravity that's holding the sun, earth, moon, etc. in their orbit around each other without the distances increasing.

Answer 5

It's speculated that a form of energy dubbed 'dark energy' is causing the expansion of space, but only at the largest scales.

Answer 6

Their mass is close to infinity as we observe it. However, an "observer" on that galaxy would observe that it is our mass that is close to infinity. Each observer sees changes only in something in motion with respect to himself. He does not see changes in his own mass because he thinks that he is at rest and everybody else is moving..