We do not see space expanding locally. What expansion there is at a particle level is resisted so they are not moving farther apart then rebounding…they are holding together the whole time. Think of it like tension in a rope. Even if that rope is stretched by the tension in this case it is a constant tension that is always there. For example without space expansion two atoms might be 1" apart. With the expansion they are 1.00000000000001" apart. Thing is we have always seen the 1.00000000000001" measurement because it is always there. Note those numbers are totally made up for illustration and bear no resemblance to reality whatsoever.
Certainly we see the expansion on large levels. Indeed that is why we know about it. Hubble made the initial observations in the 30’s.
Nope (other than telescopes ;)). If you designed a local experiment (well you’d probably have no chance unless you did this experiment in outer space) to measure the change in distance due to the expansion between points A and B, one km apart, your distance measurement would have to be accurate to a change in distance of about one 10^-15 meters per second. Not possible with today’s experimental weaponry, and probably not ever.
One hypothetical end to the universe is The Big Rip. In The Big Rip, the expansion of space accelerates until even things that are very close (say, the molecules in your body) are moving apart faster than the speed of light. From a human perspective, that would be a Bad Thing.
With my calculator (an hp 48gII), I was able to just type in 80 km/s/Mpc, 1 m/yr/au, hit convert, and it did the work for me. But I’ll go through this step by step.
I agree there.
Wikipedia says that a parsec is roughly 31 trillion kilometers, or 3.1x10^13. Mega means million, so a megaparsec would be 3.1x10^19 km. The number you divided by in this calculation represents the number of km in a gigaparsec.
We’re agreed here again.
Previously you used the number of gigaparsecs in a kilometer instead of the number of megaparsecs so you were three digits off. You converted that number to a percentage though and used that number here, which went the other way two digits, thus ending up one digit off.
In fairness, I likely would’ve made a mistake or two myself if I had to do all that by hand like you did. That’s a lot of work compared to just typing the original value into the calculator followed by the units to convert it to and hitting convert. The units feature is one of my favorite features about this calculator.
That’s very cool (that Google can do that). I had no clue it would do that for you. I’ll need to play with it some to get a sense of how it works but still…way cool (since I do not have an HP-supercool calculator of my own ).
This gives you an idea of how much the universe is expanding on a more human-sized scale. That basically means that for two objects one meter apart, the expansion of space is pushing them apart at 2*10[sup]-18[/sup] meters per second. To get an idea of what kind of speed that is, going at that speed it would take you 100 million years to traverse one hydrogen atom. Quite sluggish. Also quite undetectable and negligible in pretty much any experiment you can think of.
And if the two objects each weigh 1 milligram, the acceleration due to gravity is 6.67x10[sup]-17[/sup] m/s[sup]2[/sup] so that quickly overcomes the expansion of space.
Think about the universe expanding as an explosion (Pretty much accurate) the big bang flung things out with such a great amount of force that it is still expanding today (extremely simplified, countless other factors are at work here) like a bomb exploding each little piece of the bomb moves rapidly away from its center and therefore further away from each other. The universe is, in fact expanding from a central point, if it were expanding from all areas at once (which violates the laws of gravity among other things) galaxies would never collide which they do, all the time. In fact the Andromeda Galaxy (our intergalactic neighbor) was recently discovered to be blue shifted which means its coming toward us and not away (this works kind of like the dopplar effect only with light) it will probably collide with the milky way some time in the distant future.
If all galaxies were moving away from a central point, then after 13 billion years, there should be a huge void of emptiness around that point. Instead, we see a homogeneous distribution of smaller voids (which are still really big compared to galaxies), which is consistent with the model of the expansion happening equally everywhere. Instead of one single bubble, it’s multiple adjacent bubbles, each of which are inflating.
This is actually exactly wrong, pretty much - it’s not an expansion of matter (an explosion) but an expansion of space, as many posters above have pointed out.
Galaxies certainly could overcome the speed of expansion. The gravitational attraction between galaxies is immense. Andromeda’s blueshift (which, incidentally, was not recently discovered - we found out in 192) is primarily cited as evidence for galactic clustering around a central point. No one knows whether a collision will happen - certainly no one calls it “probable” with any legitimacy - since we don’t know its proper motion, that is, its motion across the sky rather than just towards or away.
sorry i had a really informative post addressing all the problems you had with mine but the site logged me out and I lost it. You are right about andromeda not being that recent. I feel like your splitting hairs when you say that my analogy of an exploding grenade is not correct as it succinctly illustrates the expansion of space in so far as the expanding matter is a metaphore for the galaxies expanding. Space as a mathematical factor cannot expand only the things that space is separating can grow further apart in this way space is “expanding” if this is indeed what you meant by this it is your explaination that is incorrect. In that my explaination of the universe’s expansion is incorrect it was only very basic. Nearly every current theory on universal expansion is based on the principal that it either is majorly influenced by or at the least was at first due to inertia which is the basis of Hubble’s Model which was the basis of my post. other recent theories are a small part of much larger universal equation theories, the Higgs boson theory, the M-theory, various Higgsless theories and more since no one knows what the “right” answer is I was merely trying to give everyone a basis by which to understand most of the current theories on the market today. Also, andromeda has been monitored and it is strongly predicted that it will collide with the milky way but none of us need worry about that as it is still several googol years in the making.
Not at all. There are many conclusions that would fall out of your hand-grenade model which aren’t observed, and many observed effects that aren’t explained by your model. For example, try and explain these:
-How did the early universe expand faster than the speed of light if the expansion was in matter and not the metric?
-Why isn’t there a “hole” where there is no matter at the center of the original explosion?
-The cosmic microwave background radiation is uniform in absolutely all directions - if we were flying out from some central point, wouldn’t we expect to see a blue shift in the direction we are going and a red shift away?
-Galaxies, other than Andromeda, are all moving away from us observationally - they all are redshifted - and the amount of redshift depends on distance. But wouldn’t we expect that stars in the direction of our explosively-driven travel would be less redshifted (since we are moving towards them while they move away) than ones in the opposite direction (since we are both moving away from the central point)? This isn’t observed.
This is an important distinction.
No, space itself can certainly expand. Mathematically, you just describe it as a change in the metric over time. The “expansion of the universe” works exactly that way - that’s what the FLRW metricis, and it’s the standard model of cosmology which you are citing.
Indeed, the expansion of the universe is often referred to as the “Metric expansion of space” with the hopes of avoiding this confusion.
While you are quite right that inerta is usually described as the dominant factor in the early universe, it is not the dominant factor now. The cosmological constant and “dark energy” seem to be. This is the current “Hubble constant” model.
I don’t know of any connections between M-theory and the expansion of the universe, although I’m not a string theorist, I’m just a lowly observational astronomer. But I’m intrigued! Could you send a cite?
Reasonable people can disagree about whether a collision will occur, since predictions are just based on pretty poor estimates of the proper motion of Andromeda. But it certainly won’t be “several googol years,” almost all estimates peg it in the region of 5-10 billion years. You might be reading “GYr” wrong.
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