I don’t understand the underlined bit here. Even if there were/is a point in the universe from which everything evolved, how would we know which direction to point our telescope? Hasn’t making more and more powerful telescopes just proven that we are never going to be able to view our universes limits? It’s not like we are going to find a wall at the extent of our vision, is it?
OK. I knew that but hadn’t thought about it. I withdraw my statement.
It doesn’t matter in what direction you point the telescope. The “point” from which everything evolved has expanded and now encompass the whole universe. If you look at something long away enough, you’re looking at the origin of the universe, regardless of the direction.
You couldn’t “see” back past about 400k years following the initial expansion; the density of matter was such that electrons and protons existed only in a free state, and thus the universe was opaque to photons. Only after atomic matter condensed (into hydrogen, helium, and lithium) were photons able to travel freely; those that have not been captured make up the cosmic microwave background, now a very low temperature (2.7K) photon “gas” that has cooled as the universe has expanded. The earliest thing we can observe is the 21cm line radiated by neutral hydrogen due to hyperfine splitting.
And regardless of where you look, you’re looking “back” at the origin, whether you’re pointing a telescope at the quasars near the edge of the observable universe, or at the details of subatomic structures; the Universe is everywhere, and echos of its birth resonate back and forth. If you just had a really powerful and all-knowing calculator (i.e. Laplace’s Demon) and a strictly deterministic physical universe then you could extrapolate said knowledge from a grain of sand; unfortunately, we know (or at least it is apparent) that the universe is not uniquely deterministic on the smallest scale we can probe, and so our ability to see into the past is nearly as limited as seeing into the future.
Stranger
If there is, we should destroy them before they destroy us.
I don’t think Bryan is quite the diplomatic envoy we were looking for! 
This sentence is grammatically incorrect. Nothing outside the solar system is close by for colonization purposes. Therefore, it is a known untruth, & the verb should be in the subjunctive. 
Nuke 'em from orbit.
What. We were going to get to that point eventually.
It bears repeating what the others above have said - there’s no ‘direction’ you can follow to the point of the big bang. People tend to thing of the big bang like a firecracker - something exploded and flung everything out, and its’ all traveling away from the center point.
If that were the case, then the relative speed between us and other celestial objects would vary based on the direction we looked - galaxies that were ‘flung out’ from the explosion in the same direction we were would be traveling beside us with no relative velocity between us, and things that were flung out in the opposite direction would have twice the velocity we have, and it would all converge back to a point.
But what you find when you look out into the universe is that no matter which direction you look, everything is receding from everything else. That means there’s no ‘center point’ from which we were all ejected. Rather, space itself is expanding - a better, but not perfect, analogy would be points on the surface of a balloon. Partially inflate a balloon, then draw dots all over it. Now start blowing up the balloon more. The dots all start moving away from each other. From the standpoint of any one dot, all the others are moving away from it. There’s no dot that has other dots getting closer, and no dots that are stationary with respect to others. The whole thing is growing.
The reason the balloon analogy isn’t perfect is because it still sort of suggests a center - the middle of the balloon. But that’s not the case, but if you think in terms of the entire universe expanding in every possible direction, you’ll be closer to a good visualization of what’s happening.
The reason you see earlier stars when you look far away isn’t because you’re looking in the direction of the big bang - it’s because you’re looking back in time. The farther you look, the older the light is that you’re receiving. You can look in any direction to see remnants of the big bang - you just have to look far enough that the light you see was generated when the big bang happened (actually, as Stranger pointed out, the only light you’ll be able to see is the first light generated, which happened several hundred thousand years after the big bang - until then, the universe was too hot and dense for electrons to recombine with ions, so the universe was just an opaque plasma. When it expanded enough that the temperature dropped to the point where electrons could recombine with ions, the universe suddenly became transparent.
Another misconception is that looking this far lets you see the ‘edge’ of the universe. That we’re in a big balloon that has its edge some 13.7 billion light years from here. But that’s not the case. The universe may be absolutely immense. It was all created 13.7 billion years ago, but it could be trillions of light years in size. It might be so vast that the 13.7 billion light year sphere that we can observe is a mere speck in it. We can’t see farther than that because we can only observe at the speed of light (i.e. you can’t see further, because light from objects 25 billion light years away will not have reached us yet). But it’s entirely possible that if you were magically transported a trillion light years from here, you’d be in another 13.7 billion light year observable bubble.
We’ve done some measurements which would support the notion that the universe is really much bigger. For example, we’ve measured the topology of space, and it turns out to be really flat. This is a surprising result, because space should be curved unless the average matter density is so exactly on the money that it exactly flattens space. But the other possibility is that space is curved, but the universe is so huge that any local curvature we can measure approximates flatness.
One nit I forgot to pick - everything is moving away from everything else, if it’s not gravitationally bound. We are gravitationally bound to our nearest galaxies, so the rule doesn’t apply. In fact, the Andromeda Galaxy is going to collide with us. Our galaxies are bound to our supercluster of galaxies. It’s at the largest scales where everything is moving away from everything else.
There will come a time, billions of years from now, when all we’ll be able to see is our own supercluster, and all the information about the big bang will be lost. If a new civilization evolves then, they wouldn’t necessarily ever know that a big bang happened. They might just see one big cluster of close galaxies and a huge void beyond.
Nitpick: the comoving distance to the edge of the observable universe–that is to say, the distance from an observer in an inertial frame to an object which light once emitted is now redshifted to unobservability, i.e. it appears to be moving at the speed of light–is about 46 billion light years away, though due to continued expansion of the intervening space the light was actually only about 40 million light years away when first emitted. This is due to the distance-proportional expansion of space which itself can and does exceed c at very long distances. This may sound counterintuitive but in fact the same thing happens, except in reverse, in a black hole (i.e. light emitted by an object that passes the event horizon is redshifted to nothingness from the perspective of an outside observer) and indeed many of the cosmological characteristics of the expanding universe resemble nothing so much as a black hole turned inside out, or (from the inside) running backward in time.
Also, Sam’s example of an expanding balloon is not as imperfect as he fears. Certainly, from a three dimensional perspective the balloon as a definite geometric center, but someone existing solely on the surface of the balloon, unable to measure or discern any distance in the radial (outward) direction, isn’t going to be able to point to a center. In fact, if you simplify our experiential universe to the two dimensional curved surface of the balloon, and call the radial dimension “time” with an axis labeled t, the analogy is an exact one; the center of the universe is in the t direction at time τ=0.
Stranger
That’s new to me and I don’t understand it. Wouldn’t the universe have to expand at a speed higher than light speed for this to be possible?
Yeah! If we destroy them, how can we use them as slaves?!
Yes. There is no relativistic limitation to the rate of expansion of spacetime, a fact often exploited to come up with Star Trek-esque workarounds to the limitation that mass-energy is limited to less than c, and radiation (electromagnetic, gravitational, nuclear interactions) goes only and exactly at c (although in order to use this, you have to come up with some kind of exotic negative vacuum pressure fairy dust that, as far as we know, doesn’t exist and likely wouldn’t be stable if it did). To be precise, we know that EM charge carriers (photons) move at c, we have good reasons to believe that mass charge carriers (gravitons) move at c, and it is assumed that the other gauge bosons (W, Z, and gluons) move at c, though their movements are confined to such a small interval that we can’t even measure it.
All we really know about anything that may or may not be outside the observable universe is that it is accelerating away from us at greater than c, and short of some miracle space warp drive we’ll never see into that part of our past. We do know from sky scans (WMAP) that no part of the universe appears to be repeated elsewhere, so it doesn’t seem that the universe is smaller and the observable boundary, i.e. warped back upon itself like a Klein bottle, which is good because unless the topology were trivial it might create problems with global orientability (i.e. an Alice handle) that would severely strain the laws of cosmological physics as we know them.
People like to conceive of the Big Bang as a point in space, but in fact, it is a singularity in time of infinite (or practically infinite) energy density; it might have been infinite in spacial extent to begin with, and the expansion we see is merely that already infinite volume becoming a larger infinite volume.
Did we bust your head yet?
Stranger
Moving on to the Star Trek angle - if the universe is in fact huge in relation to the 13.7 billion light year observable sphere we exist in, then that would suggest that faster-than-light travel will never be invented, and is not possible.
The logic goes like this: If the universe is infinite, or even orders of magnitude larger than ours, and if the laws of physics are the same everywhere, then you can calculate the odds of an identical world like Earth appearing elsewhere just through random chance, and it’s not infinite. That would imply that every possible variation on an ‘Earth’ and every other conceivable way that life might form also exists. And if faster-than-light travel was possible, then the first civilization to discover it could start creating self-replicating machines to populate the entire universe. And in fact, if it’s possible, then there would be huge numbers of such civilizations. We would have reached a new technological singularity in which the nature of the entire universe would have changed in a very short period of time.
But we don’t see any evidence of that. There may be other civilizations that have created self-replicating machines and completely dominated their own observable universe, but we’ll never know because we can’t interact with them, and they can’t interact with ours. And once we limit the possibilities to our own visible universe, the odds start to drop enough that we can plausibly say that it’s possible that intelligent, spacefaring life with replicating machines could evolve elsewhere in our own universe, but they just haven’t done so yet.
In other words, when constrained to a single 13.7 billion light year sphere, ‘statistically possible’ does not necessarily equate to ‘certain’ or even ‘likely’. But when the numbers get truly immense, ‘statistically possible’ starts to converge on ‘certain’.
Starting when, though? It’s entirely possible we are the first intelligent species ever to evolve in the universe. Also possible that while life is common in the universe, intelligent life is extremely rare; look how long it took to emerge on Earth.
And, they might even taste good!
Well… I must say I’m quite surprised. It’s not like I’m versed in physics but these are things I think I should have known. A little like suddenly discovering that the Earth orbit the Sun or something similar after having always assumed it was the other way around. In this particular case, I always assumed (and indeed I had no reason to make this assumption) that the universe was expanding at the speed of light, uniformly.
So, is the universe expanding at an unknown but uniform rate, or is the expansion rate dependant on the distance from the observer, with no upper limit?
Look at it this way: Let’s say that space is expanding at a fixed rate, like our balloon inflating. In that case, an object a certain distance from you will be moving away at a certain speed, but an object twice as far will be moving at twice the speed.
Take a sheet of elastic material, and draw dots on it. Now stetch the sheet uniformly, and watch the dots. The ones closet to each other will move apart slowly, but if you measure the rate of change between two dots at either end of the sheet, it will be much faster than the ones close to each other. The sheet is expanding at a uniform rate per unit area, so the effect multiplies as the distance increases.
An astronomer named Edwin Hubble (the Hubble telescope is named for him) first discovered this - he found that when measuring distant objects, the light from them red-shifted in proportion to how far away from us they were. The farther you look, the more red shift you see. Red shift indicates velocity - the more red shift, the faster the thing is moving with respect to us. At some point, the light will never reach us at all, because our relative velocities are higher than the velocity of light. Anything beyond that distance is completely outside our ability to observe.
That’s what I alluded to earlier when I said that billions of years from now we will lose all evidence of the big bang. As time goes on and the universe continues to expand, things not bound to us by gravity will continue to red-shift away. Eventually, we will not be able to see anything other than our local cluster of galaxies (Which by then may have merged into a huge globular cluster of mostly burned-out stars or something). All other objects we can see today will be outside of our light sphere. A civilization evolving at that time would have no knowledge of anything but the stars that are still gravitationally bound to each other. They’d have no reason to believe in a big bang because they’d have no evidence of it. There’s a good science fiction story in there somewhere, I’d imagine.
Unless you are assuming that Earth developed along some optimal path and that it’s flatly impossible for a technological society to emerge quicker than ours did (a claim that seems extremely suspect), then this logic doesn’t hold.
As the size of the universe grows to infinity, ‘exceedingly rare’ converges on ‘certain’. That’s my point. The argument you are making only works if the numbers are relatively small, when ‘exceedingly rare but possible’ is still meaningful. That may be the case in our observable universe.
My point is that if faster than light travel is truly possible, then the whole of the universe is visible to every ‘light sphere’ like our own within it. If that’s the case, and those light spheres can interact, then the near-infinite nature of the universe implies that we should be absolutely inundated with other species and their faster-than-light spaceships.
I think it would be exceedingly arrogant to suggest that the earth represents the absolute earliest possible moment that life of our complexity could have evolved anywhere. You could make the claim that it couldn’t have evolved until we’d gone through enough generations of stars to produce rocky planets rich in heavier elements, but that still gives you a window of billions of years.
In our own civilizational evolution we’ve gone through catastrophes and social breakdowns which set us back by hundreds or thousands of years. The Dark Ages, for example. Had those not occurred, you can speculate that it’s entirely possible that we could have had a technological civilization 500 years ago. And given the observed rate of change of technology compared to the glacial rate of general planet development and evolution, we must assume that it would have been possible for complex life to appear and form technological societies at least millions of years before us. And if it’s even remotely, infinitesimally possible, then given a big enough universe, it’s certain to have happened. And once you have faster-than-light travel and replicating machines, it would only have taken one of them to completely populate and change the entire universe over that period of time.