New Study Shows Universe Still Expanding On Schedule 173
The Bad Astronomer writes "A century ago, astronomers (including Edwin Hubble) discovered the Universe was expanding. Using the same methods — but this time with observations from an orbiting infrared space telescope — a new study confirms this expansion, and nails the rate with higher precision than done before. If you're curious, the expansion rate found was 74.3 +/- 2.1 kilometers per second per megaparsec — almost precisely in line with previous measurements."
Re:8 year old's question (Score:3, Informative)
Re:8 year old's question (Score:4, Informative)
Nothingness. There is no space & time outside the physical universe. If that doesn't bake your noodle, I don't know what will.
The nice thing about Religion^H^H^^H^H^ science is that it advances one funeral at a time. (With apologies to Max Planck :)
Re:Units (Score:5, Informative)
Due to expansion, the speed of objects accelerating away from us is proportional to the distance from us. So according to this, an object at 1 megaparsec from us will be receding at 74.3 km/s, while an object at twice the distance will be moving twice as fast.
Re:Units (Score:4, Informative)
No, a *parsec* is 3.26 light years. A Megaparsec is 3.26 MILLION light years.
Re:8 year old's question (Score:5, Informative)
Unless you have a generic curiosity, don't try to hard to read that, as it is not related to the universe's expansion. The grandparent was just being random or joking. A Hilbert space is just what you get when you treat the set of all continuous functions as a vector space. It has several different possible basis sets of functions you can add up to make any other function, e.g. sine waves via Fourier analysis. Instead of having unit vectors like x, y, and z, you would have unit vectors like sin(x), sin(2x), sin(3x), etc. (which makes it infinite dimensional). The concept is really important to physics, especially quantum mechanics and any where else things like Fourier analysis would be done with some mathematical rigor. But it is not what the universe is expanding into.
The typical analogy used for what the universe is expanding into is like a balloon being inflated, with that being a 2D universe on the surface of the balloon. You could ask about the third dimension it is expanding into, but that is not really relevant (at the moment at least). The only thing that really matters is the curvature of local space (how non-flat any given spot on the balloon is). Short of discovering some new theories unlike what we've seen before or something like brane theory, the equivalent of the 3D dimension in the balloon analogy would be unreachable and meaningless, as it would not be able to affect things in anyway beyond the curvature of the surface.
Re:Units (Score:5, Informative)
Re:8 year old's question (Score:5, Informative)
"There is no space & time outside the physical universe.
Are you sure? How do you know?"
He doesn't need to know: that's a per-definition fact.
A different question would be if the physical universe is composed of four dimensions or there are more.
Re:Units (Score:5, Informative)
Space itself can expand such that the objects (events?) within it are moving apart at faster than c. Any two objects separating faster than c can't measure that -- they cannot pass any signal between them. Any light (or other signal) which leaves one will be redshifted away to nothing before it gets to the other. They are outside each other's observable universe. I'm pretty sure this has to handled using General Relativity, I don't think Special Relativity has any concept of expanding or contracting space-time. Space-time described by Special Relativity is flat and static.
Re:Not to be pedantic (Score:2, Informative)
Doppler shift. Seriously.
Light can experience doppler shift like sound can (well, really any wave can see a doppler shift). So if two objects are moving away from each other, light from one to the other will be red shifted. If two objects are moving closer together, the light will be blue shifted.
Since chemicals have known spectral emission/absorption lines, you use that data compared with your observational data of distant objects to figure out the actual shift. Add in some math and you can even figure out how fast they are going. Hubble was one of the first to do the observations and noticed that *everything* outside the local group was red shifted. Andromeda and other members of the local group are gravitationally bound, including our galaxy, so you get other interesting values, including a blue-shifted Andromeda which gives us the idea that it will eventually collide with our galaxy as we more accurately measure that.
But if the universe wasn't expanding, you'd expect that you wouldn't see such consistent and uniform redshifts in EVERY direction. And this concept has been backed up with data using a specific type of supernovae as a "standard candle" to figure out distances and confirm that the redshifts are telling us what we think they are telling us. Everything with bigger redshifts we've been able to also measure with a standard candle has been further away from things with smaller redshifts.
The thing is, this red shift is also what allows us to measure the size of the observable universe, because this measured expansion is so uniform. And the constant used to describe this expansion is the Hubble constant. This particular bit of science isn't exactly new either. Hubble did the work almost a century ago now.