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Depends on how you look at it. If the inflationary phase of the "whole" universe never stopped, and the universe we see is just one bubble of many that "dropped out" of the inflation when that area decayed to a lower energy state, there is no way any of them would ever "run into" each other or be causally linked in any way; they would be moving away from each other at an ungodly high speed.
The inflationary phase of the Universe will eventually stop. Eventually all particles will decay and we will be back to a quantum state, where virtual particles pop in an out of existence. The total energy of our Universe is zero, everything we see and dont see is on borrowed time.
I'm loving reading this thead! Always, since earliest age, wanted to be a Cosmologist and study quantum mechanics, astrophysics, space and time etc... sadly, flunking even simple algebra nixed that idea
So i'm content with reading Hawking, Neil deGrasse Tyson, Einstein, and anything the library has to offer on cosmic subjects, and buying Videos about the universe .... doesn't mean i understand most of it, but i sure enjoy it!! (hope you don't think i'm silly)
You would also enjoy a friend of mine's video called "A Universe from Nothing", you'll find it on YouTube it was originally presented at AAS 2009. The authors name is Lawrence Krauss. From a laymans perspective, he translates why what we know is what it is. Its an excellent video if you like Tyson. Tyson is an interesting character, he's so energetic and enthusiastic all of the time and makes a lot of jokes to keep the audience attuned. He also has a lot of original thoughts. One of his videos, on the philosophy of science with Richard Dawkins is a great one too you might like on YouTube again.
Math isnt required to understand physics. What is required to understand physics is translating the every day aspects of what we've unveiled into something we can understand. Becoming a post doc in physics is what requires the math. On the quantum side, nothing is obvious and the math is strongly fundamental in understanding why the world is the way it is, however you can still understand the underlying concepts without the math.
If only all of the astrologers were astronomers think how much further our civilization would be!
Quote:
Originally Posted by NightBazaar
You're not alone. I do the same thing. The accelerated expansion is more noticable in extremely large scales of the universe. The filaments of the cosmic web structure of the universe seems to suggest that. At much closer local scales though, the expansion really isn't noticable because such objects are still gravitationally bound together.
Dark Energy is suspected to be the culprit for the acceleration of the expansion, but there isn't enough known about Dark Energy, whether it's a property of space, a completely different force, or what. We just don't know. But at larger scales we have a pretty good idea that the expansion rate is greater than Gravity can handle. Some suspect that if there are other unknown extra spatial dimensions, gravitons (hypothetical elementary particles) may be leaking out of our familiar 3-dimensional spatial configuration and slipping into more complex extra-dimensional configurations. On the other hand, it's possible that what's being termed as "Dark Energy" might be Gravity manifesting itself with a different characteristic, rather than being an attractive force, maybe its become a repulsive force. We don't know that much about Gravity or extra dimensions either.
We're pretty sure its dark energy, but we have another decade before we'll probably be much more certain. On the extra dimensions note, gravitons being defined as the "particle of gravity" in laymans terms doesnt "leak" in other dimensions. Its the only force that acts on all spacial dimensions. What that means is gravity can travel in all of our dimensions, but in order to see it, we have to have much more sensitive instruments to detect such subtle movements. Our instruments today arent anywhere near close enough to do this, but we're getting there.
Quote:
Originally Posted by NightBazaar
Yes. They're right there. See them? Right over there.
Or maybe like Schrodinger's cat, your car keys both exist and don't exist at the same time. You'll only know if they still exist if they can be found.
lol :-)
I received a PM about "why our Universe makes it look like we're in the center". We are in the center of the Universe as relative to us. What does that mean and why is that though? We can see 13.7 billion light years away from us in *every* direction. That's because the big bang occurred 13.7 billion light years ago. That doesnt mean the Universes edge is 13.7 billion light years away -- it means that light has only had 13.7 billion light years to travel. In 300 million years, we'll be able to see 14 billion light years away. Its our cosmic horizon. That horizon increases 1 light year per year! Lets say you did instantly transmit yourself 13.7 billion light years away from Earth. Your NEW cosmic horizon, relative to your new location, means you are still in the center and everything around you goes out as far as 13.7 billion light years. So to anyone, you are the center of your own Universe. But it is not the center of all that exists, its just the limit on how long light can travel to you based on the age of the Universe.
Thanks everyone for a fun thread so far, lets keep it coming!
The inflationary phase of the Universe will eventually stop. Eventually all particles will decay and we will be back to a quantum state, where virtual particles pop in an out of existence. The total energy of our Universe is zero, everything we see and dont see is on borrowed time.
Check your ignition.
In some models, the inflationary phase does indeed continue forever in at least some parts of the universe.
In some models, the inflationary phase does indeed continue forever in at least some parts of the universe.
This is very true. And a good time for a disclaimer of course. Not every answer we physicists have is the right answer. All we can say instead of a "Yes" to a question is "Based upon the current evidence and modeling we have available, it appears that it should, yes." New data and new theories / models can always change how we think of things in the future. I personally believe that once the Universe cools completely, meaning all particles have decayed, there's nothing left to expand. That's my "Yes" right now. :-) :-)
We're pretty sure its dark energy, but we have another decade before we'll probably be much more certain. On the extra dimensions note, gravitons being defined as the "particle of gravity" in laymans terms doesn't "leak" in other dimensions. Its the only force that acts on all spacial dimensions. What that means is gravity can travel in all of our dimensions, but in order to see it, we have to have much more sensitive instruments to detect such subtle movements. Our instruments today arent anywhere near close enough to do this, but we're getting there.
It would be very interesting to know what's going on out there (re: dark energy). Lawrence Krauss also said this about Dark Energy. It's label we use which basically means we don't know what it is right now. I'm sure I'm just paraphrasing it, but he's right. We don't know exactly what it is. What we know about it is from the effects that can be detected. But if you can conclusively solve it, they might just name it "Ben Energy".
The term, "leak," was used for lack of a better term for the sake of easier visualization. But assuming that there are extra dimensions (which we don't know for sure), we have absolutely no idea what those extra dimensions would be like. They may be too small for current instruments to detect, although there are some hopes that the LHC might provide some indirect clues pointing to extra dimensions. Or they might be too large for current instruments to detect.
If gravitons exist, then it provides another link to better understand the universe. While gravitons are hypothetical particles, it'd be pretty likely that there would be any Gravity without them. I think we can safely assume that gravitons would be extremely tiny particles. In the course of the evolution of the universe from the very moment (zero time) the Big Bang until now, there is nothing to say that gravitons must be solely confined to space-time (3 spatial dimensions + 1 dimension of time). If there are other dimensions within the universe, then it is at least possible that gravitons could drift into an extra-dimensional configuration to less available in our familiar 3-dimensional configuration. That doesn't mean gravitons would cease to exist, but for our purposes, they might as well. The universe might well have more spatial dimensions then the 3 we know about. The problem is that we have no idea what it would be like in a configuration of 4 or 5 spatial dimensions, which includes our 3. It's those extra dimensions that are unavailable for viewing, and even if we detect clues of extra dimensions, that doesn't mean we'd have a direct view of how it would work. So could gravitons "drift" or be absorbed by an extra-dimensional configuration? Beats me, but there's nothing to say it can't.
Think about this. Gravity is considered the weakest of the 4 known fundamental forces. It's the oddball. We don't know that much about it, although we know its an attractive force. It's powerful enough to hold entire planets, stars, galaxies, superclusters, etc., together. So why are we able to pick up a pebble off the ground so easily. The gravity of the planet should be strong enough to "glue" that pebble to the ground, and yet we can lift it up, against gravity, with ease.
It's the weakness of Gravity that raises the question, why is gravity so weak. Some physicists think that it's possible that gravitons might be small enough to exit the 3-D space of our universe and slip into a higher configuration of extra dimensions. Whether that's how it is or not, is anyone's guess.
We have a pretty good model of the Big Bang, that it began with a brief period of Inflation, which would've been many times faster than the speed of light. Following Inflation, the universe began Expansion. It was slowing down at the space of the universe grew larger. I suspect that slowing down of growth was probably due to Gravity. It was thought that the space of universe showing still be slowing down, but it was discovered that it wasn't slowing down, but had begun accelerating at increasing rates. Gravity has somehow been losing it's grip on the growth of the space of the universe. While Gravity works fine at smaller scales, it's not working very well at all at extremely large scales.
My point is that it is possible that gravitons (over very large scales) could be drawn into spatial dimensions that are higher in number and more complex than our three spatial dimensions. It's also possible that Dark Energy might turn out to be a different side of what is now the force of Gravity. Another possibility is that Gravity might go through oscillating stages of strength and weakness as the space of the universe continues expanding. Who knows, at some point in the future, gravity could get the upper hand again and begin compressing the universe back to square one. At the moment, that doesn't appear to be the case, but there's no reason to think it couldn't happen.
So what were you saying again? Oh yeah, that gravitons don't "leak" in other dimensions, and that Gravity is the only force that acts on all spatial dimensions. It might not be the ONLY force that acts on all spatial dimensions. Enter, what it termed "Dark Energy". Do we actually know Dark Energy isn't a different force? It would appear that it too acts on all spatial dimensions. While with local objects Gravity still rules. But at larger scales, it appears to be losing out. How would you know that gravitons don't leak out in other dimensions? If they do, then Gravity could become weaker (becoming more diluted) by spreading out into extra-dimensional configurations (I'm beginning to hate that word) if there's a finite supply of gravitons in the universe. If somehow the supply is closer to infinite, or that it can somehow be replenished, that too would have to raise some questions. It appears that the more the space of the universe increases, the weaker Gravity gets at large scales, ultimately to the point that it's effect would eventually reach zero.
The idea isn't something I came up with. It's a subject that's being looked at by physicists. If there's something that really wrong about it, I'm all ears. I do agree with your point, but only as it relates to what we currently know about the universe, or have good reason to believe. Sometimes though, especially when it comes to the really BIG QUESTIONS about the universe, it's not a bad thing to think outside of the box for fresh ideas.
Great thread. How about explaining the Alcubierre warp drive? The way I understand it, you contract space time in front of a spherical object (a ship) and expand space time behind it creating a "bubble" in the middle. I read somewhere that a NASA scientist has found a way to test this theory but before I even attempt to understand the bit about changing the drive's geometry, can you explain in layman's terms how you go about expanding and contracting space-time and why it would result in a form of propulsion?
You're not alone. I do the same thing. The accelerated expansion is more noticable in extremely large scales of the universe. The filaments of the cosmic web structure of the universe seems to suggest that. At much closer local scales though, the expansion really isn't noticable because such objects are still gravitationally bound together.
Dark Energy is suspected to be the culprit for the acceleration of the expansion, but there isn't enough known about Dark Energy, whether it's a property of space, a completely different force, or what. We just don't know. But at larger scales we have a pretty good idea that the expansion rate is greater than Gravity can handle. Some suspect that if there are other unknown extra spatial dimensions, gravitons (hypothetical elementary particles) may be leaking out of our familiar 3-dimensional spatial configuration and slipping into more complex extra-dimensional configurations. On the other hand, it's possible that what's being termed as "Dark Energy" might be Gravity manifesting itself with a different characteristic, rather than being an attractive force, maybe its become a repulsive force. We don't know that much about Gravity or extra dimensions either.
The best explanation I have encountered for Dark Energy thus far is the Casimir Effect, or zero-point energy.
At least it is a theory that can be tested, and has already been observed on a much smaller scale. Which is more than can be said about extra-dimensions or hypothetical particles.
Great thread. How about explaining the Alcubierre warp drive? The way I understand it, you contract space time in front of a spherical object (a ship) and expand space time behind it creating a "bubble" in the middle. I read somewhere that a NASA scientist has found a way to test this theory but before I even attempt to understand the bit about changing the drive's geometry, can you explain in layman's terms how you go about expanding and contracting space-time and why it would result in a form of propulsion?
There are several problems with Alcubierre's warp drive. Not least of which is that is relies heavily on the existence of a hypothetical particle (tachyons) or other exotic matter (negative energy). The next biggest problem is the amount of energy required. In order to travel from one end of the Milky Way galaxy to the other end would require several orders of magnitude more energy than is available in the observable universe.
If such a bubble could be created, there would be no way for those inside the bubble to control, steer, or stop the spacecraft because the ship would be completely isolated from the rest of the universe. For that reason, some have suggested a donut-shape or torus would be a better approach than a bubble. However, that still does not get past the first two major hurdles.
I think Alpha Centauri is the closest star system to Earth (about 4 light years), and they've discovered planets recently. Say we develop a fast enough engine to send a probe there. Even if a probe goes super fast and takes it only a few years to get there and back, due to relativity how long would it take in our view? Could we even send a probe to take pictures and come back in our lifetime if it left today?
Proxima Centauri is the closest star at 4.243 light years distant. The Alpha Centauri stars (A and B) are 4.366 light years away.
A spacecraft that is 99.9% anti-matter by weight, assuming 100% energy transference to thrust, would take 19 years, 3 months, 24 days to make a round trip to Alpha Centauri, from Earth's perspective. The spacecraft's thrust would be 0.22178 G (2.173444 m/s^2), and would reach 74.53% the speed of light.
In order to travel faster, it would require more fuel than could be brought. To travel at 1 G (9.8 m/s^2) it would require 450% more anti-matter fuel than the entire weight of the spacecraft. For example, to send a 1 ton probe to Alpha Centauri at 1 G thrust it would require 4.5 tons of anti-matter, which would make the entire spacecraft weight 5.5 tons, and therefore never be able to reach its destination.
Time in Seconds from Earth's Perspective = 2*SQRT((k/T)*((((D/(2*k))+1)^2)-1))
k = (c^2)/T
c = 299,792,458 meters/second (speed of light)
T = 2.173444 thrust in meters/second^2
D = 4.13E+16 distance in meters to Alpha Centauri
I would like to further amend my post. While I used the most efficient means of generating energy - anti-matter (E=mc^2), it is not the most realistic. Unless we can figure out a way to harvest anti-matter directly from the sun, nobody is going to spend the astronomical cost to produce anti-matter for fuel. Which makes a 1,000 ton spacecraft, with 999 tons of anti-matter to propel a 1 ton probe, being sent to Alpha Centauri and back unrealistic.
We still not have mastered hydrogen fusion, but next to anti-matter, it is the second most efficient means of generating energy (E=0.008mc^2), and vastly more realistic than using anti-matter. A 1,000 ton spacecraft, with 999 tons of hydrogen fuel (again assuming 100% transference to thrust) to propel a 1 ton probe, would take 97 years, 10 months, and 10 days to make a round trip to Alpha Centauri and would not be able to accelerate/decelerate faster than 0.00177285 G (0.0173739 m/s^2). The spacecraft would reach 8.91% the speed of light at its fastest point at the middle-point between the Alpha Centauri and Sol systems.
As with anti-matter, any attempts to go faster would result in running out of fuel before reaching its destination. While the amount of time may seem vast, it is actually several thousand times faster than any chemical or ion rockets we have currently produced. The distances between stars is truly vast.
The amount of energy (in joules) required is calculated as follows:
Using Anti-Matter: E = (2*(c^2))*((1/(SQRT(1-(V^2))))-1)/(c^2)
Using Hydrogen: E = (2*(c^2))*((1/(SQRT(1-(V^2))))-1)/(c^2)/0.008
V = (c/SQRT(1+(k/(T*((T⊕/2)^2)))))/c
c = 299,792,458 meters/second (speed of light)
k = (c^2)/T
T = 0.0173739 continuous thrust in meters/second^2
T⊕ = 3.09E+09 Time, in seconds, from Earth's perspective to make a round trip to Alpha Centauri
As a result, and to ultimately answer the poster's question, there is no spacecraft that could be reasonably developed that could reach Alpha Centauri and return within the span of a human lifetime.
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You're not alone. I do the same thing. The accelerated expansion is more noticable in extremely large scales of the universe. The filaments of the cosmic web structure of the universe seems to suggest that. At much closer local scales though, the expansion really isn't noticable because such objects are still gravitationally bound together.
