We used to think that about the earth, too. I would be very surprised if it is actually true. It's a matter of scale. The scale of the Earth's curvature is much greater than the size of a human being. Similarly, the scale of the universe's curvature, if it exists, is comparable to the size of the observable universe itself (if not much greater).
I expect we will eventually realize that the universe is hyper-spherical, and that time is a vector perpendicular to the surface of that hypersphere. The projection of one time-vector on another time-vector gives the appearance of time dilation, which has been interpreted as expansion. And, the radius of that hypersphere is the zero on the red-shift graph. But that is just a guess. Well, that's fairly close to a lay description of general relativity's picture of a spherical universe. All we know that if it is spherical, the sphere is so big that it looks flat on any scale we can measure. Maybe with more precise instruments we can detect a deviation, if it's there.
But don't forget that there are geometries other than "spherical" and "flat", too.
In the mean time, we can have fun with the big-bangers by asking about the other 95.38% of the mass/energy/whatever that they presently can't account for. The fact that so much is left unaccounted and unexplained tells me the flat-universe theory is, at best, not complete. That doesn't have much to do directly with a flat universe theory. It's possible for spherical universes to have dark matter and energy too.
Any true description of the universe probably should account for just about 100% of the universe. That's why our description of the universe is being expanded to include dark mater and energy.
No. They only measured microwave radiation. But it's not a single measurement. Nor are microwave measurements the only one which imply a similar age of the universe.
But all that misses my main point, which is that I none of this has anything to do with whether "nothing at all existed before 13.73 billion years ago". Such observations are currently not able to address that question. They only imply that 13.7 billion years have elapsed since the universe was in a submicroscopic hot and dense state. They cannot (yet) address the question of what, if anything, may have preceded that state.
The depth of the gravitational well that the Earth or the Milky Way is in, relative to intergalactic space, is pretty much negligible; you can treat it as Newtonian to a very high accuracy. (And astrophysicists have known about intergalactic voids for a long time; they're much bigger than a million lightyears. The Bootes void, discovered almost 30 years ago, is something like 250 million lightyears across.)
This is *not* a correct description of time dilation. As you know, if time dilation was the only issue, both the earth's clocks relative to the ship and the ship's clocks relative to the earth would run at *slower* rates. Everyone would age slower wrt to everyone else on earth and on the ship. It is the ship shifting reference frames to turn around that causes the time variable of the earth's clock to hop forward relative to the ship's clock. Well, that's why I clarified that it's a combination of time dilation and shifting frames. Sure, you don't get the result without shifting inertial frames. But you don't get it without time dilation, either; the twin comes back the same age no matter what if you let gamma go to 1.
I can't really say which of the two effects is "more important", so I would not say that the OP is totally or even mostly incorrect. I actually don't view them as two separate points. I just think of integrating proper time along two worldlines of different lengths. In the geometric picture, reference frames don't really enter in it, and you can't really separate time dilation from anything else without choosing a coordinate system (which I don't like to do, conceptually).
The phrase "for this reason" follows the previous paragraph and implies he believes *because of the twin paradox* (or is he talking about time dilation?) the speed of light is constant in all reference frames. This is backwards. You're right. (Though technically, I think you could take the results of the twin paradox as a postulate and work back to Einstein's postulate as a derived consequence, at least if you postulated the right formula for the amount of age difference... so it might be historically backwards but not necessarily logically backwards.)
From this phrase he is defining "our reference frame inside the universe" as giving a result of 13.73 billion years. Not homogenous/isotropic frames at rest wrt to the cmb. This implies he is using a "another" reference frame outside the universe to give 6000 years. I thought the OP just meant compared to a different reference frame inside the universe, which is not the Earth frame. If the OP really meant some "God's frame" outside the universe, which is possible, then you're right.
Please explain to me where "a cartoon version of SR", or SR at all, was used. Everything the OP said was correct within GR.
I think the intent of the original post was silly. What I merely object to is that it is physically inaccurate. If somebody really wants to insist that there are observers who see the universe as 6000 years old, they can. It's physically permissible. It's just not good theology (IMHO). If you want to object to something in the original post, it should probably be "Who cares the age is in another frame of reference?" I may not agree with the original poster's intent, but it's not fair to claim they were wrong on physical grounds.
That's the story "ARM". The murderer used a flashlight inside the field to cook people outside of the field. He died when the detective trapped him partly into the field, so that his limb outside the field died and inside, living much faster, he died of gangrene.
It's quite hard to be atheist when you study some of these deeply complex topics - cosmology, neurology, etc. I didn't find it hard when I was doing cosmology, and cannot imagine why I should have.
"Flat" here refers to the curvature of space. In the absence of a cosmological constant, and assuming homogeneity and isotropy, this implies that the universe is balanced on the edge between eternal expansion and recollapse. (Not an equilibrium size, but an eternal expansion that asymptotically slows to a rate of zero.) However, dark energy (at least in the simplest model) implies that a flat universe is no longer "balanced on edge", and in fact its expansion will accelerate eternally.
the history of science is a story of moving away from anthropocentric theories of reality, and the big bang is rather anthropocentric The first statement is unsupported and likely false. The second statement is pointless, as your interpretation of its "anthropocentricity" has nothing to do with its validity or the future likelihood of it being overturned.
meanwhile saying "Big Bang cosmology just says that the universe was once small, hot, and dense, and subsequently expanded and cooled" is a backtrack and understatement of what the big bang theory encompasses. it talks of a beginning friend: an infinite state of density and temperature Wrong. General relativity breaks down at singularities and can make no prediction about whether anything did or did not precede one. Furthermore, general relativity is known to be wrong since it is inconsistent with the observed behavior of matter at the quantum level, and quantum theory implies that the place where it is wrong is precisely in the vicinity of the Big Bang.
i freely admit i don't have much going for what i am saying. but at least i am not misrepresenting things like you do That's big talk for someone who obviously has never studied cosmology.
1, 2: agree 3: irrelevant if not outright meaningless
And no, you have not supported your claim about the history of science; you merely reasserted it. Tell me again where the anthropocentric bias is in the theory of the fractional quantum Hall effect.
That's not a disproof of eternal cosmologies, or at least, not yet. There is still vigorous debate about the cosmological implications of the second law of thermodynamics. When you look at eternal inflation of "bubble universes", or cyclic universes involving the collision of branes in higher dimensions, there is the question of whether regions like our universe can locally decrease entropy during a Big Bang-like event, at the expense of increasing entropy elsewhere in the universe (outside the bubbles, or off the branes).
is pretty much a story of moving away from anthropocentirc theories of reality The history of science is no such thing. Tell me that, say, the fractional quantum Hall effect is a story of moving away from "anthropocentirc theories of reality".
And, once again, it's totally irrelevant. The Big Bang was not introduced for anthropocentric reasons, and its validity is based on evidence, not with whether you choose to interpret it as "anthropocentric" or not. Therefore, any reasoning which attempts to conclude anything about the plausibility of Big Bang cosmology on the basis of constructing such analogies is logically invalid.
You're making a dumb argument by semantic redefinition.
If I travel out to Alpha Centuari at relativistic speeds and come back again, the Earth may make, say, 8 revolutions about the Sun. But I will not be 8 years older.
Ok, what's the measure? Fractional mass-energy density. That is, the ratio of the average baryonic mass-energy density to the average total mass-energy density of the universe. The matter portion has a positive mass, and the vacuum portion has a positive energy (with nonzero cosmological constant), and the two can be compared via E=mc^2.
i may be pilloried and voted as a troll by the defenders of the status quo here for saying this, No, you'll get modded up, because there's nothing that Slashdotters like more than a self-professed heretic.
but i will still say it: the big bang will be disproven. the universe is endless in time and space There are Big Bang cosmologies which are endless in time, space, or both.
Regardless, your argument is still facile. Whether you can draw an analogy between a scientific theory and human beings has no bearing on whether the theory is "anthropocentrically biased", let alone its scientific validity.
"Defenders of the status quo"? Give me a break. You're not Galileo.
now all i ask of you, in intellectual honesty, is to admit to me that the big bang theory has an anthropocentric bias to it What bias do you think that is?
The Cosmological Principle used to derive a homogeneous/isotropic cosmology is anti-anthropocentric: it assumes that the location of the Earth is not a privileged one within the universe.
Contrary to your previous post, Big Bang cosmology does not insist that the universe have a beginning, middle, and end. (Indeed, dark energy, it's looking less unlikely that it will have an end.) Nor must it have a beginning; there are plenty of eternal/cyclic variants of the Big Bang out there. Big Bang cosmology just says that the universe was once small, hot, and dense, and subsequently expanded and cooled.
[...] Correct? Within the limitations of the balloon analogy, what you said is correct, except for the "space inside the matter" bit; see below.
How can we see that the universe is bigger than it was, if our rulers are also expanding in space along with what they're measuring? They're not. (Or at least, not at a rate commensurate with the overall universe.) Systems which are electromagnetically, gravitationally, or otherwise bound resist the overall expansion of the universe. See this FAQ. They create local pockets of space that don't expand very much.
You're talking about the reference frame of the Earth. There can be other observers who can experience 6000 Earth years of subjective time, while the Earth itself experiences many more than 6000 revolutions about the Sun. But the logical possibility of such hypothetical observers isn't very interesting or relevant.
4D spacetime can be curved, but 3D space can be flat. (On average, on a cosmological scale. On the scale of galaxies and things, there are little ripples of curvature in space as well as spacetime.)
I did read the original post. It's fully correct. Of course, if you take it as an argument about Biblical exegesis, it's pretty dumb, because who cares whether there's some random observer who could potentially have observed a 6000 year age for the universe? But the physics is right: there ARE such observers. (In the mathematical sense. I don't mean that there were actual living beings who happened to follow such trajectories.)
Well yes, you can mathematically prove what the prediction of a theory is. You just can't prove that anything about the real world, such as whether the universe is open, closed, or flat. You can only give evidence supporting or contradicting such a prediction.
(The only way this breaks down is if the universe changed in overall density in the past 13 billion years. But the law of conservation of energy and matter tells us that's impossible.) The universe certainly changed in overall density: that's what happens when it expands. What you mean is if the ratio of the density of the universe to the critical density changes.
Well, in the context of anything that goes on in the observable universe today, whether the universe is positively or negatively curved doesn't make a whole lot of difference — it's either "flat" or "pretty flat". Could have been important right at the Big Bang, though.
Slashdot Mirror
But don't forget that there are geometries other than "spherical" and "flat", too. In the mean time, we can have fun with the big-bangers by asking about the other 95.38% of the mass/energy/whatever that they presently can't account for. The fact that so much is left unaccounted and unexplained tells me the flat-universe theory is, at best, not complete. That doesn't have much to do directly with a flat universe theory. It's possible for spherical universes to have dark matter and energy too. Any true description of the universe probably should account for just about 100% of the universe. That's why our description of the universe is being expanded to include dark mater and energy.
No. They only measured microwave radiation. But it's not a single measurement. Nor are microwave measurements the only one which imply a similar age of the universe.
But all that misses my main point, which is that I none of this has anything to do with whether "nothing at all existed before 13.73 billion years ago". Such observations are currently not able to address that question. They only imply that 13.7 billion years have elapsed since the universe was in a submicroscopic hot and dense state. They cannot (yet) address the question of what, if anything, may have preceded that state.
The depth of the gravitational well that the Earth or the Milky Way is in, relative to intergalactic space, is pretty much negligible; you can treat it as Newtonian to a very high accuracy. (And astrophysicists have known about intergalactic voids for a long time; they're much bigger than a million lightyears. The Bootes void, discovered almost 30 years ago, is something like 250 million lightyears across.)
I can't really say which of the two effects is "more important", so I would not say that the OP is totally or even mostly incorrect. I actually don't view them as two separate points. I just think of integrating proper time along two worldlines of different lengths. In the geometric picture, reference frames don't really enter in it, and you can't really separate time dilation from anything else without choosing a coordinate system (which I don't like to do, conceptually). The phrase "for this reason" follows the previous paragraph and implies he believes *because of the twin paradox* (or is he talking about time dilation?) the speed of light is constant in all reference frames. This is backwards. You're right. (Though technically, I think you could take the results of the twin paradox as a postulate and work back to Einstein's postulate as a derived consequence, at least if you postulated the right formula for the amount of age difference... so it might be historically backwards but not necessarily logically backwards.) From this phrase he is defining "our reference frame inside the universe" as giving a result of 13.73 billion years. Not homogenous/isotropic frames at rest wrt to the cmb. This implies he is using a "another" reference frame outside the universe to give 6000 years. I thought the OP just meant compared to a different reference frame inside the universe, which is not the Earth frame. If the OP really meant some "God's frame" outside the universe, which is possible, then you're right.
Please explain to me where "a cartoon version of SR", or SR at all, was used. Everything the OP said was correct within GR.
I think the intent of the original post was silly. What I merely object to is that it is physically inaccurate. If somebody really wants to insist that there are observers who see the universe as 6000 years old, they can. It's physically permissible. It's just not good theology (IMHO). If you want to object to something in the original post, it should probably be "Who cares the age is in another frame of reference?" I may not agree with the original poster's intent, but it's not fair to claim they were wrong on physical grounds.
You keep using that word. I do not think it means what you think it means.
That's the story "ARM". The murderer used a flashlight inside the field to cook people outside of the field. He died when the detective trapped him partly into the field, so that his limb outside the field died and inside, living much faster, he died of gangrene.
"Flat" here refers to the curvature of space. In the absence of a cosmological constant, and assuming homogeneity and isotropy, this implies that the universe is balanced on the edge between eternal expansion and recollapse. (Not an equilibrium size, but an eternal expansion that asymptotically slows to a rate of zero.) However, dark energy (at least in the simplest model) implies that a flat universe is no longer "balanced on edge", and in fact its expansion will accelerate eternally.
1, 2: agree
3: irrelevant if not outright meaningless
And no, you have not supported your claim about the history of science; you merely reasserted it. Tell me again where the anthropocentric bias is in the theory of the fractional quantum Hall effect.
That's not a disproof of eternal cosmologies, or at least, not yet. There is still vigorous debate about the cosmological implications of the second law of thermodynamics. When you look at eternal inflation of "bubble universes", or cyclic universes involving the collision of branes in higher dimensions, there is the question of whether regions like our universe can locally decrease entropy during a Big Bang-like event, at the expense of increasing entropy elsewhere in the universe (outside the bubbles, or off the branes).
And, once again, it's totally irrelevant. The Big Bang was not introduced for anthropocentric reasons, and its validity is based on evidence, not with whether you choose to interpret it as "anthropocentric" or not. Therefore, any reasoning which attempts to conclude anything about the plausibility of Big Bang cosmology on the basis of constructing such analogies is logically invalid.
You're making a dumb argument by semantic redefinition.
If I travel out to Alpha Centuari at relativistic speeds and come back again, the Earth may make, say, 8 revolutions about the Sun. But I will not be 8 years older.
Regardless, your argument is still facile. Whether you can draw an analogy between a scientific theory and human beings has no bearing on whether the theory is "anthropocentrically biased", let alone its scientific validity.
The Cosmological Principle used to derive a homogeneous/isotropic cosmology is anti-anthropocentric: it assumes that the location of the Earth is not a privileged one within the universe.
Contrary to your previous post, Big Bang cosmology does not insist that the universe have a beginning, middle, and end. (Indeed, dark energy, it's looking less unlikely that it will have an end.) Nor must it have a beginning; there are plenty of eternal/cyclic variants of the Big Bang out there. Big Bang cosmology just says that the universe was once small, hot, and dense, and subsequently expanded and cooled.
You're talking about the reference frame of the Earth. There can be other observers who can experience 6000 Earth years of subjective time, while the Earth itself experiences many more than 6000 revolutions about the Sun. But the logical possibility of such hypothetical observers isn't very interesting or relevant.
4D spacetime can be curved, but 3D space can be flat. (On average, on a cosmological scale. On the scale of galaxies and things, there are little ripples of curvature in space as well as spacetime.)
I did read the original post. It's fully correct. Of course, if you take it as an argument about Biblical exegesis, it's pretty dumb, because who cares whether there's some random observer who could potentially have observed a 6000 year age for the universe? But the physics is right: there ARE such observers. (In the mathematical sense. I don't mean that there were actual living beings who happened to follow such trajectories.)
Well yes, you can mathematically prove what the prediction of a theory is. You just can't prove that anything about the real world, such as whether the universe is open, closed, or flat. You can only give evidence supporting or contradicting such a prediction.
Well, in the context of anything that goes on in the observable universe today, whether the universe is positively or negatively curved doesn't make a whole lot of difference — it's either "flat" or "pretty flat". Could have been important right at the Big Bang, though.