Voyager 1: to the edge of the Solar System
Launched in 1977, that's one loooong trip.
(only a matter of time before it collides with an alien ship and becomes Veeager -- but that is the future.)
here
Quote: rxwineLaunched in 1977, that's one loooong trip.
Has that great 8 track player and Beta video tape technology on board. Somebody pinch me..
Quote: JerryLoganHow far STRAIGHT out does space go?
As least as far as the longest tape measure ever made. Thats far enough for me..
Quote: rxwineOr very close ...and perhaps to intersteller space in about 4 years.
Launched in 1977, that's one loooong trip.
I remember reading some years ago that NASA never dreamed that Voyager would last this long--it would, of course, keep going on its trajectory no matter what, but it wasn't expected to continue to function and transmit data for so long.
Quite a piece of engineering.
On the other side, we find more universes. No reason to think ours is the only one...
I think you're thinking galaxies.Quote: dwheatleyOn the other side, we find more universes. No reason to think ours is the only one...
The universe is singular, and is supposed to be all-encompasing. Yet, to describe it as expanding does beg the question....
But the question "What's on the other side?" does not apply
The universe is NOT expanding. It's just that the contents of the known universe are getting further apart.
If we peer to the edge on, say, the "up" side (over the north pole), we guess ... 15 billion years old. If we peer to the "bottom" ... or left, right, back, forward, we guess the same amount.
Are we at or near the center? What are the chances of that?
If we aren't near the center, wouldn't we guess, say, 5 billion peering "bottom" or 11 billion peering "left" or 9 billion peering "right"?
If we can't see the edges, then how can we use them for guesses? If we don't see the edges as different distances away, are we to assume we're at the center like the flat-earth people in the dark ages?
NB: the question holds if you sub in "furthest seeable object" for "edges."
Quote: JerryLoganSo if it keeps on going STRAIGHT out into infinity, where does it end? I know, the question so twisted MKL's mind that he came up with a mobius ribbon or some stupid thing just so he didn't have to put any thought into it. Now's the chance for you brainiacs to deliver and prove you can do more than move that slide rule back & forth. How far STRAIGHT out does space go?
I think this assumes spacetime is "straight" which may not be the case.
If you walk in a straight line on the earth (on any Great Circle), you will end up exactly where you started. The third dimension of surface curvature brings you home.
It's been posited that spacetime may be similarly curved in a fourth physical dimension (which pretty much exists). In other words ...
If you fly in a straight line in space (on any Great Circle or whatever they would call that), you will end up exactly where you started. The fourth dimension of spacetime curvature brings you home.
This, I think, is called a "closed universe."
Quote: DJTeddyBearThe universe is NOT expanding. It's just that the contents of the known universe are getting further apart.
This is just semantics. If we heat up the air inside a balloon, does the balloon expand, or do the contents get further apart? To me, it's the same thing.
As for what's on the other side: there certainly could be something on the other side, if our notion of the universe as encompassing everything is flawed. If you are a fish living in the water, you wouldn't understand the concept of land or space, but it's still there. Multiple universes occupying the same meta-space is not my idea, just my favourite.
Quote: rxwineLaunched in 1977, that's one loooong trip.
I think my name, along with those of millions of others, is etched on a gold disk attached to the spacecraft (along with a map of our solar system, and recordings of "greetings" in many languages...) I vaugely recall my school participating in some NASA publicity stunt at the time to develop interest in the program.
As an aside, what kind of batteries last for 33+ years?... Nuclear. Many eons from now, a whole alien planet is going to be really pissed when this radioactive waste falls from the sky onto one of their pre-schools. Of course with my luck, the only thing that survives that disaster will be the gold disk with my name on it and a map back to Earth. I apologize now to my future ancestors who will have to deal with the open can of alien whoop-ass.
Quote: AyecarumbaI apologize now to my future ancestors who will have to deal with the open can of alien whoop-ass.
Wasn't that the premise of Battlefield Earth? Some aliens found Voyager out in space, followed the map back to earth, killed 99% of us, and turned the other 1% into slaves. If not Battlefield Earth then the 10-book "Mission Earth" series by the same author.
Quote: WizardWasn't that the premise of Battlefield Earth? Some aliens found Voyager out in space, followed the map back to earth, killed 99% of us, and turned the other 1% into slaves. If not Battlefield Earth then the 10-book "Mission Earth" series by the same author.
Scientologists? I recall that "Battlefield Earth" was made into a movie with John Travolta. I've never seen it, since I heard that it stunk.
Quote: IbeatyouracesMany scientists think that the universe is expanding. Using this theory there has to be a theoretical "end" to the universe and this begs the question, if there is an end to the universe, and everything is contained in the universe, then what the heck is on the other side?
One does not imply the other. The expansion of the universe means that more space is constantly being created everywhere, pushing the galaxies apart from each other.
It does not require the spatial extent to be finite, although, the most commonly accepted point of view is that the universe is finite after all. That again does not mean that it has an "end". The surface of a sphere, for example, is finite, but does not have boundaries.
Quote: ItsCalledSoccerI
It's been posited that spacetime may be similarly curved in a fourth physical dimension (which pretty much exists). In other words ...
If you fly in a straight line in space (on any Great Circle or whatever they would call that), you will end up exactly where you started. The fourth dimension of spacetime curvature brings you home.
This, I think, is called a "closed universe."
Close, but not quite. First, curvature is an inherent property of the manifold (space), and does not require additional dimensions to exist. There is no fourth spacial dimension (there are actually 10 dimensions in string theory, but that's a different story, irrelevant to to this question), but that does not mean that the space is necessarily flat.
Also, strictly speaking, it does not have to be curved to be finite and unbounded. A surface of a 4d torus is technically flat (it has zero curvature), yet finite. Something that appears "curved" from a higher-dimensional view, may very well be internally flat. A familiar example is a surface of a cylinder - it is created by protruding a curve (circle) vertically, but is euclidean (i.e., does not have any curvature).
"Closed universe" is a term for a universe having positive curvature (like a sphere or a cone), "open universe" is a universe with negative curvature (like saddle shaped), and "flat universe" is euclidean space (a 4-torus essentially) with zero curvature. An interesting tangent is that "closed universe" is finite not only in space, but also in time - at some point the expansion will change to contraction, everything will get closer and closer together, creating a singularity (a "black hole" containing all the matter), and time will come to an end. Open and flat models on the other hand are both infinite in time.
There is a large and growing amount of evidence in cosmology, that our universe is actually flat in this sense.
Quote: weaselman
There is a large and growing amount of evidence in cosmology, that our universe is actually flat in this sense.
Well, I couldnt prove the earth is flat so now I will just go with "the universe is flat"
as for space-time curving, isnt that something that can't be detected by observation, sort of in the same way that the speed of light always is the same when measured?
Quote: AyecarumbaAs an aside, what kind of batteries last for 33+ years?... Nuclear. Many eons from now, a whole alien planet is going to be really pissed when this radioactive waste falls from the sky onto one of their pre-schools.
Many eons from now it will be harmless, except as dead weight.
Odds are no one and nothing will ever run accross either Voyager, or to the Pionneers X and XI, by accident. And given likely costs, no one will launch an expedition from Earth to retrieve them.
Quote: NareedMany eons from now it will be harmless, except as dead weight.
Odds are no one and nothing will ever run accross either Voyager, or to the Pionneers X and XI, by accident. And given likely costs, no one will launch an expedition from Earth to retrieve them.
I think you took him too seriously.
I have just about finished "The Universe", the History Channel series, and will review it soon [season one that is]. I've really enjoyed it.
Quote: odiousgambit
as for space-time curving, isnt that something that can't be detected by observation, sort of in the same way that the speed of light always is the same when measured?
Well, first of all, we are talking about space curvature here, not space-time curvature, and second, being the inherent property of the manifold, it most certainly can be detected by observation.
Speaking of space-time curvature for example, we observe it constantly by experiencing gravity (the essence of the Einstein's general relativity is equating gravity to the curvature of space-time). Detecting the curvature of space is kinda trickier, because it, if exists, is going to be very very tiny, way beyond the accuracy of our measuring devices. If the curvature was significant, it could trivially be detected by a simple geometric procedure such as measuring angles of a triangle (in flat space the sum of all angles is exactly 180 degrees, in a curved one, it will be more or less, depending on the sign of the curvature) or dividing the circumference of a circle by the radius, and noting the deviation of the result from Pi.
The thing about curvature of the space is that it is connected to the total amount of matter (or, more precisely, on energy density ) in the universe. If that amount is equal to a certain value, the space is flat, if it is greater, we have a closed universe, otherwise it is open.
The latest estimates come up with values just shy of the critical mass (they used to be way, way lower actually, but with the addition of dark matter and dark energy, are now almost hitting the mark), suggesting that the universe might be slightly negatively curved. However, that assumption causes other problems (basically, cosmological equations show, that a universe that was curved after Big Bang would have to become more curved with time, while a flat universe would remain flat. Given, that the current curvature, if any, is really tiny, it seems unlikely that the universe was initially created with such a minute curvature. A more logical conclusion would be that the universe really is flat, and it is our mass estimates that are a little off).
Quote: dwheatleyQuote: DJTeddyBearThe universe is NOT expanding. It's just that the contents of the known universe are getting further apart.
This is just semantics. If we heat up the air inside a balloon, does the balloon expand, or do the contents get further apart? To me, it's the same thing.
As for what's on the other side: there certainly could be something on the other side, if our notion of the universe as encompassing everything is flawed. If you are a fish living in the water, you wouldn't understand the concept of land or space, but it's still there. Multiple universes occupying the same meta-space is not my idea, just my favourite.
I don't think it's just semantics at all.
Some people have likened the expanding universe to raisin bread baking. That is, all the raisins in the loaf are moving away from each other as the loaf expands. Add to that that the loaf sits in an oven whose walls don't move at all. In that scenario, the universe (oven walls) is NOT expanding even though everything (raisins) is moving away from everything else. (Not a perfect analogy, but hopefully illustrative.)
Using the balloon, heat up the air inside the balloon. If you're using a microwave oven, then it's the same deal: oven stays the same size while all the contents of the balloon get further apart. Or, heat it up inside a room: walls of the room stay the same size while all the contents of the balloon get further apart.
These are just illustrations and analogies, which all break down at some point, but it tells the story of how the universe could NOT be expanding and yet everything is still moving away from everything else.
Quote: weaselmanOne does not imply the other. The expansion of the universe means that more space is constantly being created everywhere, pushing the galaxies apart from each other.
It does not require the spatial extent to be finite, although, the most commonly accepted point of view is that the universe is finite after all. That again does not mean that it has an "end". The surface of a sphere, for example, is finite, but does not have boundaries.
Close, but not quite. First, curvature is an inherent property of the manifold (space), and does not require additional dimensions to exist. There is no fourth spacial dimension (there are actually 10 dimensions in string theory, but that's a different story, irrelevant to to this question), but that does not mean that the space is necessarily flat.
Also, strictly speaking, it does not have to be curved to be finite and unbounded. A surface of a 4d torus is technically flat (it has zero curvature), yet finite. Something that appears "curved" from a higher-dimensional view, may very well be internally flat. A familiar example is a surface of a cylinder - it is created by protruding a curve (circle) vertically, but is euclidean (i.e., does not have any curvature).
"Closed universe" is a term for a universe having positive curvature (like a sphere or a cone), "open universe" is a universe with negative curvature (like saddle shaped), and "flat universe" is euclidean space (a 4-torus essentially) with zero curvature. An interesting tangent is that "closed universe" is finite not only in space, but also in time - at some point the expansion will change to contraction, everything will get closer and closer together, creating a singularity (a "black hole" containing all the matter), and time will come to an end. Open and flat models on the other hand are both infinite in time.
There is a large and growing amount of evidence in cosmology, that our universe is actually flat in this sense.
Heh ... give me a break, I did it in just a couple of lines of text! Hell, you can't even explain scientifically thoroughly how a fart stinks up the room in a couple of lines!
Its sometimes related as :: hey you guys can't answer the question so I can understand it, therefore scientists have some sort of hidden agenda, therefore God exists.
Quote: ItsCalledSoccerHeh ... give me a break, I did it in just a couple of lines of text!
Yeah, but it was a wrong explanation :)
The loaf of bread is expanding inside the oven, and the walls of the oven are not moving ... because the loaf is smaller than the oven, that's all. If it was the same size, it would either stop expanding, or the oven would have to expand with it.
This is not what happens with the the expansion of the universe at all, not even as an illustration.
For the analogy to be correct, the loaf itself should be equated to the universe, not the oven (not everything inside the oven is moving away from everything else - everything otside the loaf of bread is stationary). The universe (loaf) is most certainly expanding, as in becoming larger in volume. This is indeed a proper analogy, but it does not help to answer the original question, because loaf of bread is bounded.
Quote: weaselmanYeah, but it was a wrong explanation :)
The loaf of bread is expanding inside the oven, and the walls of the oven are not moving ... because the loaf is smaller than the oven, that's all. If it was the same size, it would either stop expanding, or the oven would have to expand with it.
This is not what happens with the the expansion of the universe at all, not even as an illustration.
Careful ... the "couple of lines" comment referred to spacetime and the curvature of space, not the loaf analogy.
It's true that if it was the same size, it would either have to stop expanding or the oven would have to expand with it. Or the loaf might start to contract.
But the illustration holds. If there's some "oven wall" out there that the expansion hasn't yet hit, and the universe is defined as "everything inside of those oven walls," then it holds. We don't know this; we only know about what we can see (the loaf). If you define the universe as "the loaf," then the oven walls would be something outside the universe that might contain it. Either way, the illustration holds.
Note that I don't necessarily think it's the way things are. It's just that the illustration holds.
Quote: ItsCalledSoccer
Careful ... the "couple of lines" comment referred to spacetime and the curvature of space, not the loaf analogy.
Ah, yeah. Well, that one was, like I said, almost right, if not for two wrong points - the implication that compact manifold must be curved in order to be unbounded, and the notion of fourth spatial dimension, that does not really exist (not in the way you present it anyway).
Quote: ItsCalledSoccer
But the illustration holds. If there's some "oven wall" out there that the expansion hasn't yet hit, and the universe is defined as "everything inside of those oven walls," then it holds.
Well, yeah ... IF that was the case, THEN the illustration would be correct. But it's not, so it isn't.
Quote:We don't know this;
Yes, we do.
Quote:we only know about what we can see (the loaf).
We actually know lots of stuff about things we can't see. Superstrings, black holes, Big Bang, etc. etc.
If you are saying we can't be totally, absolutely, and completely sure, I'll give you that.
We can't even be sure that the universe with all its content, including us, and our own "memories" has not just jumped into existence a moment ago (in some sense, it can be argued, that thermodynamically it is more probable than Big Bang, and 14 billion years of evolution).
Everything is possible, but some things are just more sensible than others.
Quote:If you define the universe as "the loaf," then the oven walls would be something outside the universe that might contain it.
I don't know what you call "universe" then. There is nothing "outside the universe" in the definition I use, because universe is the very thing that contains everything.
(There is also a multiverse theory, but that's more of science fiction than science, and not much to do with the loaf anyway).
Quote:Note that I don't necessarily think it's the way things are. It's just that the illustration holds.
Well, if you are saying that it holds, but just doesn't illustrate the way things are, then, I guess, I can agree :)
PBS was showing a feature on Mandelbrot last night (pretty sure it was a repeat)
This convinced me that atoms /solar systems/ galaxies and the Universe itself is the result of a fractal equation. As they all tend to have indivdual systems with swirling componets in different sizes.
Quote: weaselmanAh, yeah. Well, that one was, like I said, almost right, if not for two wrong points - the implication that compact manifold must be curved in order to be unbounded, and the notion of fourth spatial dimension, that does not really exist (not in the way you present it anyway).
This never made intuitive sense to me. If the universe is expanding, then it has to be claiming its new territory somehow. This, I think, is a pretty good indicator of a fourth physical dimension. Whether or not there is some ultimate limit (whether "oven walls" or contraction due to gravity) is still under debate. But if contraction is an ultimate possiblilty, then there we have our "oven walls," existant for intrinsic reasons rather than a superdimensional "boundary" that's just out there somewhere ... but an "oven wall" nonetheless.
I get a little confused ... at one point you mention that, just because we can't see things doesn't mean they're not there. Then, you say that, we can't see a fourth dimension so it doesn't exist. Some clarification would be helpful.
Quote: weaselmanWe can't even be sure that the universe with all its content, including us, and our own "memories" has just jumped into existence a moment ago (in some sense, it can be argued, that thermodynamically it is more probable that Big Bang, and 14 billion years of evolution).
This stood out to me as it closely resembles some arguments I've heard for a 8,000 (or whatever) year old universe in line with biblical timelines. If there is a God who indeed created the universe, then I would have no problem assigning to that God the power to create things with the appearance of age.
I always thought it made more sense to think of it in relativistic terms; that is, relativity has shown us that the exact same events can take very different amounts of time, depending on your perspective. Note that I don't necessarily think relativity explains the apparent discrepancy in biblical and cosmological age estimates, but it would make a little more sense to me than an arbitrary creation-with-apperance-of-age.
But hey, God didn't consult me on that issue.
Quote: ItsCalledSoccerThis never made intuitive sense to me. If the universe is expanding, then it has to be claiming its new territory somehow.
I know, it does not make intuitive sense. Our intuition simply isn't trained on things like higher dimensions, or (even more so) "the entire space", because all our experiences happen IN space, it is impossible to imagine an object with no space at all outside of it, but universe is exactly this object. There is no space or "territory" to claim for the simple reason that all the "territory" is already inside the universe.
This unintuitive stuff in science is more of a rule nowadays than an exception, and it's only going to get worse in the future. The times of mechanistic models are long gone.
Quote:
Whether or not there is some ultimate limit (whether "oven walls" or contraction due to gravity) is still under debate.
It is? Who is debating it? Can you provide some references to the "oven walls" proponents?
Quote:But if contraction is an ultimate possiblilty, then there we have our "oven walls," existant for intrinsic reasons rather than a superdimensional "boundary" that's just out there somewhere ... but an "oven wall" nonetheless.
No, not at all. Contraction, like expansion, does not imply a boundary or an existence of anything besides (outside) the manifold itself.
Quote:I get a little confused ... at one point you mention that, just because we can't see things doesn't mean they're not there. Then, you say that, we can't see a fourth dimension so it doesn't exist. Some clarification would be helpful.
I did not say that anything can exist that we do not see. For some things that we can't see, we can find some indirect evidence. The existence of others we can deduce theoretically by exploring a theory that also produces observable results that we can verify. And finally, we can just arbitrarily say "God/fourth dimension/ether/foobar/unicorn/whatever exists because it makes intuitive sense to me".
This last approach, while has its indisputable advantages, is not very productive as far as understanding the reality goes.
Quote: IbeatyouracesMany scientists think that the universe is expanding. Using this theory there has to be a theoretical "end" to the universe and this begs the question, if there is an end to the universe, and everything is contained in the universe, then what the heck is on the other side?
I was always taught that the universe MUST be expanding unless it is contracting. Gravity would dictate that it cannot remain static. But this begs the question--where is the end of the universe if we can't be sure what it the beginning, center, and end? Couldn't we define the "end" of the universe several galaxies away or the parking lot of Circus Circus equally?
Quote: weaselmanIt is? Who is debating it? Can you provide some references to the "oven walls" proponents?
Is this a serious question? Whether or not the ultimate fate of the universe is eternal expansion or ultimate contraction is a HUGE topic and far from settled.
So .... let me try another way ...
When we look at the stars, we see that, no matter which direction we look, we are looking back about 15 billion years. This implies that we are at or near the center of the universe since, in all directions, we see 15 billion years back. I don't speak for cosmologists, but the concept of being at the center of the universe is, i think, very uncomfortable to that group, and is reminiscent of most of the dark ages where something similar (albeit for different reasons) was believed.
Going back to the loaf of raisin bread in the oven analogy ...
Pick an arbitrary point in the loaf and call it our location. Then, draw a 15 billion light year sphere around it, call it a hollow golf ball. We know about everything inside the surface of the hollow golf ball because the speed of light is constant, and everything that has reached us comes to us radially along the golf ball's radius. From our perspective, the universe is spherical and we see the same distance in all directions. Within the hollow golf ball, all the raisins are still moving away from us, and the universe is still expanding.
But ... the hollow golf ball (our known universe) may or may not be identically equal to the size and shape of the loaf. It would be colossolly improbable for that to be the case. In this analogy, there is more "loaf" outside the hollow golf ball, which we cannot possibly know about, but it's there.
Once you get outside the hollow golf ball, there's no difference between the remaining loaf and the oven walls. This is what I mean. If the whole "oven wall" thing confused matters, then disregard it. It's just an analogy meant to promote understanding, and all analogies are imperfect and break down.
Note: this illustration has one key assumption: that we are NOT at the center of the universe. If we are, and if we have the bravery to acknowledge that, IF that were the case, then the rest of this breaks down.
It implies that 15 billion light years is the current limit of the most powerful telescopes.Quote: ItsCalledSoccerThis implies that we are at or near the center of the universe since, in all directions, we see 15 billion years back.
But to screw with people's heads for a second...
Those telescopes can look in all directions (albeit not at once), anything beyond their 15 billion light year limit is unknown.Quote: ItsCalledSoccerNote: this illustration has one key assumption: that we are NOT at the center of the universe.
Therefore, it is not a mistake to say that we are at the center of the known universe.
Quote: DJTeddyBearI agree with most of what what you said, except this:It implies that 15 billion light years is the current limit of the most powerful telescopes.
But to screw with people's heads for a second...
Those telescopes can look in all directions (albeit not at once), anything beyond their 15 billion light year limit is unknown.
Therefore, it is not a mistake to say that we are at the center of the known universe.
That's an interesting side-point. Who's to say that, just because we can only see a certain amount back in time, that that time MUST be the age of the universe? What if we knew everything else we know now, but could only see 8,000 years back? Would we call it conclusive proof that the biblical account was true? Or would we leave room that there are things yet to be discovered and figured out?
And, if we're so quick to give ourselves the benefit of the doubt and say we still need to figure things out if we could only see 8,000 years back, why are we so married to our "conclusive proof" just because it's 15 billion years instead of 8,000? It seems arbitrary and irrational to me, and is damn sure unscientific.
Of course, the easy answer to that is the fossil evidence that goes back much further than 8,000 years. But by slipping in "biblical", you're inviting people to suggest that when the world was created, fossils that appear very old were created at the same time.
Quote: DJTeddyBearNow you went and done it. You slipped the word "biblical" in there...
Of course, the easy answer to that is the fossil evidence that goes back much further than 8,000 years. But by slipping in "biblical", you're inviting people to suggest that when the world was created, fossils that appear very old were created at the same time.
Ummm ... nope. You're seeing something that's not there, but thanks anyway for assigning motive.
:eyeroll:
Quote: rdw4potusI think the Biblical account is only 8000 years old if you adhere to a very strict (and somewhat mis-translated) version of Genesis 1:1-31. My understanding is that every line that says "on the _ day, God _" is more accurately translated as "in the _ age, God _"
Young earth creationists claim about 6000 years old, based on a back working of the age of the prophets and the long line of ages and begats in the book of Genesis.
Quote: DJTeddyBearNow you went and done it. You slipped the word "biblical" in there...
Of course, the easy answer to that is the fossil evidence that goes back much further than 8,000 years. But by slipping in "biblical", you're inviting people to suggest that when the world was created, fossils that appear very old were created at the same time.
I already talked about that in an earlier post, but think about it this way ...
Consider the twins paradox, where the first twin goes on a journey near the speed of light for a while and the second twin stays on earth. When the first twin returns, he is, say, 3 years older. But the second twin is, say, 80 years older.
Now think of things from the first twin's perspective and take away all knowledge of time dialation. The first twin returns and says, "I've only been gone a couple of years, how in the hell did you get so old?" The second twin says, "You haven't been gone a couple of years, you've been gone 80 years."
Who's correct, the first or second twin? Answer: they're both correct.
Extending the analogy, let's say that someone goes on a near-light-speed trip when the big bang happened. Look at things from the traveler's perspective and take away all knowledge of time dialation. He travels around for, oh, 8,000 years and comes to earth. The traveler says, "I've only been traveling for 8,000 years, how the hell is the universe 15 billion years old?" An earthling says, "All the fossils and the sun and the speed of recession of the other galaxies and background radiation and whatever else says the universe isn't 8,000 years old, but 15 billion."
Who's correct? The traveler who says the universe is 8,000 years old or the people on earth who say it's 15 billion? Answer: they're both correct.
Again, I don't necessarily think that relativity provides an explanation for the age difference between the bible and cosmology. I just wonder why, since we know about relativity, we don't seem to really open to applying the fact that the same event can take very different amounts of time, depending on your perspective, to that particular discussion.
Hmmm....Quote: ItsCalledSoccerI already talked about that in an earlier post, but think about it this way ...
Consider the twins paradox, where the first twin goes on a journey near the speed of light for a while and the second twin stays on earth. When the first twin returns, he is, say, 3 years older. But the second twin is, say, 80 years older.
Now think of things from the first twin's perspective and take away all knowledge of time dialation. The first twin returns and says, "I've only been gone a couple of years, how in the hell did you get so old?" The second twin says, "You haven't been gone a couple of years, you've been gone 80 years."
Who's correct, the first or second twin? Answer: they're both correct.
Extending the analogy, let's say that someone goes on a near-light-speed trip when the big bang happened. Look at things from the traveler's perspective and take away all knowledge of time dialation. He travels around for, oh, 8,000 years and comes to earth. The traveler says, "I've only been traveling for 8,000 years, how the hell is the universe 15 billion years old?" An earthling says, "All the fossils and the sun and the speed of recession of the other galaxies and background radiation and whatever else says the universe isn't 8,000 years old, but 15 billion."
Who's correct? The traveler who says the universe is 8,000 years old or the people on earth who say it's 15 billion? Answer: they're both correct.
Again, I don't necessarily think that relativity provides an explanation for the age difference between the bible and cosmology. I just wonder why, since we know about relativity, we don't seem to really open to applying the fact that the same event can take very different amounts of time, depending on your perspective, to that particular discussion.
That actually makes a lot of sense.
For the record, I simply like to invoke the "You've opened a can of worms" thing, when someone brings the bible into a scientific discussion.
Quote: ItsCalledSoccerIs this a serious question? Whether or not the ultimate fate of the universe is eternal expansion or ultimate contraction is a HUGE topic and far from settled.
Yeah, I was asking about "oven walls" debate, not the ultimate fate.
Quote:When we look at the stars, we see that, no matter which direction we look, we are looking back about 15 billion years. This implies that we are at or near the center of the universe since, in all directions, we see 15 billion years back.
I don't speak for cosmologists, but the concept of being at the center of the universe is, i think, very uncomfortable to that group, and is reminiscent of most of the dark ages where something similar (albeit for different reasons) was believed.
Indeed, it is so "uncomfortable" (I would say, in fact, downright ridiculous), that, I think, it should just tell you right away that there is something wrong with your line of reasoning that takes you to such a ridiculous conclusion.
Imagine that you live on the surface of a sphere. Where is the "center" of your 2-d "universe"? The fact is, that every point on the sphere is exactly like any other. Your "view" from each point is exactly the same. If the sphere is being inflated, then you can pick any point on it, and see all other point uniformly rushing away from it in all directions, just as if you were in the center.
Quote:Pick an arbitrary point in the loaf and call it our location. Then, draw a 15 billion light year sphere around it, call it a hollow golf ball. We know about everything inside the surface of the hollow golf ball because the speed of light is constant, and everything that has reached us comes to us radially along the golf ball's radius.
In fact, we know (or can assume) more than that.
We know that the universe is about 15 billion years old, and that it has started from what we can consider a "single point", so we can tell, that, if our model of the world (the General Relativity) is correct, nothing can be farther than 15 billion light years from any point in the universe.
Could the GR, the Friedman model, the inflationary theory, the superstring theory just all happen to be completely wrong, and we are really living in gigantic "loaf of bread", sitting in an even more gigantic "oven", that we just can't see because it's too far away?
Well ... sure, it could ... Or it could be, that everything, including our memories and perception of reality just jumped into existence a moment ago ... Or, we could all exist inside a huge supercomputer ...
There is no reason to assume any of the above possibilities though, so, it appears more productive to stick with the generally accepted view for the time being, until it is demonstrated to be incorrect or insufficient.
Quote: DJTeddyBearFor the record, I simply like to invoke the "You've opened a can of worms" thing, when someone brings the bible into a scientific discussion.
A pot-stirrer, are we? ;-)
I don't think the two are very far separated at all. My thinking is in the same camp as Sagan, who acknowledged that the two fields were brought close together and posed some extremely difficult questions.
Quote: ItsCalledSoccer
Now think of things from the first twin's perspective and take away all knowledge of time dialation. The first twin returns and says, "I've only been gone a couple of years, how in the hell did you get so old?" The second twin says, "You haven't been gone a couple of years, you've been gone 80 years."
Who's correct, the first or second twin? Answer: they're both correct.
No. The one, that stayed inertial (did not accelerate) is correct in the sense that his clock is showing what's known as "proper time" in the coordinates both twins are currently using.
Quote: weaselmanYeah, I was asking about "oven walls" debate, not the ultimate fate.
I think there was a disconnect there, which is why I tried a different approach.
Quote: weaselmanIndeed, it is so "uncomfortable" (I would say, in fact, downright ridiculous), that, I think, it should just tell you right away that there is something wrong with your line of reasoning that takes you to such a ridiculous conclusion.
Imagine that you live on the surface of a sphere. Where is the "center" of your 2-d "universe"? The fact is, that every point on the sphere is exactly like any other. Your "view" from each point is exactly the same. If the sphere is being inflated, then you can pick any point on it, and see all other point uniformly rushing away from it in all directions, just as if you were in the center.
This comes across as self-contradictory. It's not wrong to follow a "we're at the center of the universe" line of thinking when, as you say below, we *know* that the universe is 15 billion years old AND we can only see 15 billion years in any direction. How far back in time we can see may have absolutely nothing to do with the actual age of the universe, and if it does, would only be coincidentally so because we're at the exact center ... which, you say, is "uncomfortable" and therefore "proof" that my reasoning is wrong. Doesn't add up.
Quote: weaselmanIn fact, we know (or can assume) more than that.
We know that the universe is about 15 billion years old, and that it has started from what we can consider a "single point", so we can tell, that, if our model of the world (the General Relativity) is correct, nothing can be farther than 15 billion light years from any point in the universe.
Could the GR, the Friedman model, the inflationary theory, the superstring theory just all happen to be completely wrong, and we are really living in gigantic "loaf of bread", sitting in an even more gigantic "oven"?
Well ... sure, it could ... Or it could be, that everything, including our memories and perception of reality just jumped into existence a moment ago ... Or, we could all exist inside a huge supercomputer ...
There is no reason to assume any of the above possibilities though, so, it appears more productive to stick with the generally accepted view for the time being, until it is demonstrated to be incorrect or insufficient.
If you're meaning, go with the current view because it's the best scientific guess, then (frankly) that's a very mature point of view, IMHO. However, if it's just the best scientific guess, then what can we say we really *know* about 15 billion years?
I have no problem that science only knows what it can know, and I have no problem understanding that science, while better than it was 500 years ago, will be even better still 500 years form now, and I have no problem with science proffering its best guess when it doesn't truly know. I have a problem when Science oversteps its bounds and asserts things as true that are either false, unknown, or unknowable.
For example, we can see 15 billion light years. Science fact (or at least current best-guess).
Therefore, we *know* the universe is 15 billion years old. Science overstepping its bounds.
When Science oversteps its bounds, it becomes Religion, the very thing it professes to be the opposite of.
Quote: weaselmanNo. The one, that stayed inertial (did not accelerate) is correct in the sense that his clock is showing what's known as "proper time" in the coordinates both twins are currently using.
Both times ... and coordinates ... are equally proper.
I'm pretty sure that's where "Relativity" got its name, and I'm absolutely certain it's Relativity 101.
Quote: ItsCalledSoccer
This comes across as self-contradictory. It's not wrong to follow a "we're at the center of the universe" line of thinking when, as you say below, we *know* that the universe is 15 billion years old AND we can only see 15 billion years in any direction. How far back in time we can see may have absolutely nothing to do with the actual age of the universe, and if it does, would only be coincidentally so because we're at the exact center ... which, you say, is "uncomfortable" and therefore "proof" that my reasoning is wrong. Doesn't add up.
Refer to my surface of sphere example. Any point on it can be considered "a center" in the sense you are using that term. There are no special points on the sphere, and similarly, there are no special points in the universe.
The number of light years we can see happens to be the same as the number of years since Big Bang not by coincidence, and not because we are "in the center", but simply because of our choice of units.
Quote:If you're meaning, go with the current view because it's the best scientific guess, then (frankly) that's a very mature point of view, IMHO. However, if it's just the best scientific guess, then what can we say we really *know* about 15 billion years?
"Scientific guess" is really an oxymoron. It's either a guess or it is scientific.
I would say, we "know" about 15 billion years with about the same level of confidence that we "know" that perpetuum motion is impossible, or that we do not all live in a matrix, or that God did not create the earth and heavens in 7 days, or that a winning betting system is impossible etc...
Quote:I have no problem that science only knows what it can know, and I have no problem understanding that science, while better than it was 500 years ago, will be even better still 500 years form now, and I have no problem with science proffering its best guess when it doesn't truly know. I have a problem when Science oversteps its bounds and asserts things as true that are either false, unknown, or unknowable.
I think, your problem is that you choose to arbitrarily declare things "unknowable" if they don't "make intuitive sense to you". It seems a little shortsighted to me.
Quote:Both times ... and coordinates ... are equally proper.
No, there is only one "proper time" in any frame of reference. When the two twins meet, one of them has the proper time in their common frame, and the other one does not. Relativity does not equate to ambiguity.
Quote: weaselmanI think, your problem is that you choose to arbitrarily declare things "unknowable" if they don't "make intuitive sense to you". It seems a little shortsighted to me.
Quote: weaselmanNo, there is only one "proper time" in any frame of reference. When the two twins meet, one of them has the proper time in their common frame, and the other one does not. Relativity does not equate to ambiguity.
Given that you believe these things to be true when they're not, I'm not sure where else the discussion can go. But here goes ...
Quote: weaselmanRefer to my surface of sphere example. Any point on it can be considered "a center" in the sense you are using that term. There are no special points on the sphere, and similarly, there are no special points in the universe.
I think you said earlier there were only three spatial dimensions. The sphere example, carried forward, would assume at least a fourth spatial dimension. So that comes across as self-contradictory.
As far as inertial reference frames, relativity deals with velocity, not acceleration. While you have to accelerate to get to relativistic velocities, the effects aren't felt because of acceleration, they're felt because of velocity.
Lastly, there's nothing ambiguous about relativity. It's a scientific fact that the same event can take two very different lengths of time, and both lengths are correct.
Quote: ItsCalledSoccerGiven that you believe these things to be true when they're not, I'm not sure where else the discussion can go. But here goes ...
It's not the question of a belief. It's just the definition of the term "proper time". There is not wiggle space, there is exactly one thing in each reference frame that's called that, no matter what one may believe.
Quote:
I think you said earlier there were only three spatial dimensions. The sphere example, carried forward, would assume at least a fourth spatial dimension. So that comes across as self-contradictory.
No. The sphere is a compact 2-dimensional manifold, it does not require the third dimension to exist. Imagining it as the surface of a three-dimensional ball aids your intuition, but that's it, there is no real need for the additional dimension. Likewise, a 3-sphere is a 3-dimensional manifold, no fourth dimension is needed.
Note also, that I am not actually saying that the universe is spherical (unlike other things we talked about, this is something we don't really know, but the evidence so far seems to be more in favor of a toroidal topology rather than a sphere). I only mentioned sphere as an example to demonstrate the lack of necessity of the notion of "center" when describing unbounded manifolds.
Quote:As far as inertial reference frames, relativity deals with velocity, not acceleration.
While you have to accelerate to get to relativistic velocities, the effects aren't felt because of acceleration, they're felt because of velocity.
Well ... kinda ... yes and no. There is a subtle point here that makes this statement wrong.
While both twins are inertial, their views are equivalent and symmetrical, you can't tell which one is moving. If you ask twin A, he'll tell you that B's clock is slower than his, but B will tell you that A's clock is slower.
The symmetry breaks when one of the twins turns around (accelerates) to come back and compare the clocks. Now there is an objective difference between the two twins, because one of them stayed inertial all the time, and the other one did not.
The proper time of the inertial frame is always longer than a non-inertial one. This is just a geometric property of the Minkowsky space, similar to the familiar notion of a straight line being the shortest distance between two points in the familiar Eucledian space.
Quote:It's a scientific fact that the same event can take two very different lengths of time, and both lengths are correct.
This is true as long as you understand that "correct" here really means "corresponds to the proper time of some inertial observer". In this sense, an even stronger statement holds - there is actually an infinite number, not just two of possible values.
Quote: WizardWasn't that the premise of Battlefield Earth? Some aliens found Voyager out in space, followed the map back to earth, killed 99% of us, and turned the other 1% into slaves. If not Battlefield Earth then the 10-book "Mission Earth" series by the same author.
1) In L. Ron Hubbard's novel Battlefield Earth, aliens who stumble on a Voyager probeproceed to find and conquer Earth.
2) Star Trek: The Motion Picture (1979) features an alien intelligence V'ger, which turns out to be a fictional Voyager 6, highly transformed.
3) In the X-Files episode "Little Green Men" in Season 2, Special Agent Fox Mulder hears part of the golden record played back to him in an extraterrestrial transmission received at Arecibo Observatory.
4)John Carpenter's 1984 movie Starman opens with the Voyager 1 probe being intercepted by an alien spacecraft, whose occupants play the golden record.
5) In Futurama episode Parasites Lost the Voyager probe can be seen stuck on the window of the spaceship as Leela is wiping it off the windshield.
6) In Star Trek IV: The Voyage Home (1986) To save Earth from an alien probe, Kirk and his crew go back in time to retrieve the only beings who can communicate with it, humpback whales. The alien probe learned the song of the humpback whales from the golden record on Voyager. If the humpback whales don't respond then the earth will be destroyed. Of couse, mankind has driven them to extinction, thus requiring the trip backwards in time.
Star Trek IV was the most financially successful of the Star Trek movies except for the revival in 2009 with the new cast. It was probably the only movie that didn't take itself seriously, but relied on jokes about trying to interpret the 20th century.
The following whale researchers were given Thanks in the credits for Star Trek IV
Mark Ferrari .... thanks
Debbie Glockner-Ferrari .... thanks
Roger Payne .... thanks
