[fifeboy]

It goes from over there to over there!

[PublicAnimalNo9]

billypilgrim billypilgrim:

"If the universe IS finite, what do you think we'd find at the end of it... a wall, another universe, or just empty space?"

douglas adams wearing nothing but an ipod. "oh, hello raydan. just enjoying the new kanye west album. ..care for a martini? "

I'd rather have a Wisgean Zoda thanks

[Zipperfish]

Khar Khar:

I also loved that they brought up Dark Matter, but I wish they had gone into more detail. Dark Matter is suggested to take up perhaps 80% of all matter in the universe, while conventional matter, or matter we recognize, takes up only 20%. That means that those elements on our table only make up 20% of what we are looking at in space. The rest we can only infer. Only a little of this dark matter may be from MACHO, which are constructed of conventionally recognized matter. What's even more interesting is that only about 4-5% of mass energy in the universe can be attributed to matter we recognize, with the rest going to that Dark Matter.

Meh, not too enamored with the whole dark matter thing. Sounds a lot like the aether of pre-relatvistic physics. Kind of like, "the equations don't work but if we invent this stuff called dark matter and stick it in there then it works great."

Mind you, I read that aethers making a comeback in some physicist circles.

[Khar]

I disagree. I'd much prefer they recognize the existence of something which is there (as Dark Matter is broken down by varying properties exhibited) then for them to pretend something doesn't exist. We can detect that something is impacting the movement of celestial bodies, and we can determine that it's something mass related which we do not understand. That it encourages research and questioning of what this is, or if other theories are simply wrong, is excellent in my books. In fact, I can't think of a theory which Dark Matter has explained without them continuing to look into how Dark Matter works there, or why, but I'm also no expert so may be waaaay off base.

I prefer to look at Dark Matter as a way of saying "something is there, but we don't know what." It functions consistently throughout models if properly categorized into the correct type of Dark Matter, of which there are only three. In addition, there has been numerable theories about which this postulated Dark Matter could be. For example, we have discovered that some of the Dark Matter is the aforementioned baryonic particles, but not a large portion, due to MACHO tests. We understand that the effects from gravitational lensing rule out such things as black holes and galaxy sized phenomenon.

Indeed, in addition to baryonic particles we already know of other forms Dark Matter takes. For example, neutrinos are a form of dark matter, called hot dark matter because it moves at ultra-relativistic (around the speed of light). It's proposed that this matter makes up about 10% of all dark matter, or 8% of all matter. Extension research has been done into the field of neutrinos, and we've been able to detect them experimentally for over 60 years.

Also, Dark Matter continues to go under model revisions. For example, the mixed dark matter model is no longer considered valid, as the obsolete model, the ratio provided failed to stand up to experimental scrutiny and hence was expunged from a set of valid models. Even though it was a good fit, because we don't know what it is we continued researching it and this brought about the advent of dark energy.

I definitely see where you come from though. I've read enough papers with terms like "unexpected biotic factors" and other such terminology winged in there, but at the same time, it's not being used as an excuse to stop questioning the models, and I feel that's important. This all may just be me, though.

[DrCaleb]

PublicAnimalNo9 PublicAnimalNo9:

raydan raydan:

PublicAnimalNo9 PublicAnimalNo9:

Nope.

I'm guessing you can compare this to when the earth was flat and we thought if you sailed far enough, you'd fall over the edge.

If the universe IS finite, what do you think we'd find at the end of it... a wall, another universe, or just empty space?

What we'd find at the end of the universe is that which existed before it came into being. And whatever that is, is anybody's guess.
Although, when one is talking about a distance of roughly 14 billion LY, it might as well be infinite

Nope. 14B light years is not infinite, it's 14B light years. Just like 3 metres is not infinite, it's 3 metres.

As Khar alluded to, there are several competing theories to the structure of the universe. We may be in a very large 'area', where Universes are created all the time, live and die - but are so far apart we never see each other. It may fold back on itself. There may be different universes occupying the same space as us - many different theories.

Another is a 'bubble' type of universe, where the edge of the expansion from the Big Bang is the outer limit, and beyond it does not exist. Either way, to ask 'what is beyond the Universe' is kind of like asking 'what comes after plaid'. The question sort of doesn't make sense.

[PublicAnimalNo9]

DrCaleb DrCaleb:

Nope. 14B light years is not infinite, it's 14B light years. Just like 3 metres is not infinite, it's 3 metres.

As Khar alluded to, there are several competing theories to the structure of the universe. We may be in a very large 'area', where Universes are created all the time, live and die - but are so far apart we never see each other. It may fold back on itself. There may be different universes occupying the same space as us - many different theories.

Another is a 'bubble' type of universe, where the edge of the expansion from the Big Bang is the outer limit, and beyond it does not exist. Either way, to ask 'what is beyond the Universe' is kind of like asking 'what comes after plaid'. The question sort of doesn't make sense.

I was being facetious with my last comment DC

[Zipperfish]

Khar Khar:

I disagree.

$1:

I prefer to look at Dark Matter as a way of saying "something is there, but we don't know what."

I don't think you do disagree, because that is exactly what I think. I haven't seen solid reasoning as to why we have to be talking about mass, as opposed to gravity. Or perhaps--a recent paper suggested--our notion of an isotropic (unifrom in all directions) universe is wrong.

The idea of dark matter is fine, as long as it's understood that it is really just filling in gaps in equations at this point.

Gravity theory dispenses with dark matter

$1:

In this case, a hypothetical particle called a graviton - which mediates gravity - appears in large numbers out of the vacuum of space in regions crowded with massive objects such as stars. "It's as if gravity is stronger" near the centres of galaxies, Brownstein told New Scientist. "Then, at a certain distance, the stars become sparse, and the gravitons don't contribute that much." So at larger distances, gravity returns to the behaviour described by Newton.

[Zipperfish]

DrCaleb DrCaleb:

Nope. 14B light years is not infinite, it's 14B light years. Just like 3 metres is not infinite, it's 3 metres.

As Khar alluded to, there are several competing theories to the structure of the universe. We may be in a very large 'area', where Universes are created all the time, live and die - but are so far apart we never see each other. It may fold back on itself. There may be different universes occupying the same space as us - many different theories.

Another is a 'bubble' type of universe, where the edge of the expansion from the Big Bang is the outer limit, and beyond it does not exist. Either way, to ask 'what is beyond the Universe' is kind of like asking 'what comes after plaid'. The question sort of doesn't make sense.

Or there's the Many Worlds Theory of quantum physics, where a new universe is created for possible outcome of a quantum events, whihc means that virtually countless universes are creating, every instant, diverging from ours just by a single quantum event.

[Khar]

Hmm, apologies, Zipperfish, I inferred from your "not too enamoured" mention that your viewpoint differred from mine in that regard. Remember that we see effects on other things from Dark Matter not only on worlds and other cosmological entities, but also in background radiation.

However, I think it's great you brought this up, because it's true there are many alternative theories. Many quantum gravity (those who watch The Big Bang Theory, Sheldon, Leonard and Leslie all do research in this field) models exist which do in part compete with the concept of Dark Matter. The first two, Sheldon and Leonard, work in what is called M-theory, or superstring theory. Leslie, on the other hand, works on the competing theory of loop quantum gravity. Both of these theories are FAR more ambitious than what we've been talking about here since they are researching a comprehensive theory of the function of natural forces un the universe. This stuff is at the very edge of modern study, and are only part of alternative theories. It's worth keeping in mind that these theories don't necessarily remove the need for Dark Matter, but rather postulate alternatives for the base theories at this time. Experimental evidence simply doesn't exist to the degree to dismiss other theories in favour of these ones. The math works out beautifully in many of these models, but there isn't the experimental evidence to back it up.

Simply put, there is a very real possibility we are wrong about gravity. There has been research which indicates that the gravitational constant may not be so constant, for example. This is one of the reasons why I am happy with the existence of Dark Matter, since it's very existence caused people to question the foundations of other theories. While there certainly are alternatives, however, we continue to explain these unknown powers through the term "Dark Matter" even if it may be misleading as to the depth of research being conducted in various subfields in Physics, since it's the best way to say "there's something there we can't entirely explain." It's one of those fun things like how "theory" in science means something different than "theory" in mainstream use, and how "agnostic" can have different meanings inferred if used in differing contexts.

There is a bit of a difference between the Many Worlds and chaotic inflation theories. While both metaverse models, Many Worlds is based on the idea that an endless series of universes exist which cover every concievable difference from each other's. Chaotic inflation has more to do with an endless series of big bangs creating entirely new universes. String theorists have their own special setup, but they also have 11 dimensions and interpret it all with 1 dimensional strings on a 2 dimensional medium, so let's not go in there because it makes my head ache just thinking about it. The difference between the first two is that one lies in probability space, and the other in regular spacetime.

In fact, metaverse theories are broken down into a taxonomy, much like evolutionary theory has trees. Level I and Level II are both based on chaotic inflationary theory. Level III is based on Many Worlds theory, and is similar to Level I. Level IV is the theory of everything. There is no Level V.

[DrRosen]

Its much too large to carpet

[PublicAnimalNo9]

DrRosen DrRosen:

Its much too large to carpet

Galaxies. The area rugs of the universe

[DrCaleb]

PublicAnimalNo9 PublicAnimalNo9:

I was being facetious with my last comment DC

I know man. I was just expanding on a preconception that I think many people may hold. 'Infinite' is sometimes a hard concept. If you ever think I'm being too serious, look at my avatar.

[raydan]

DrCaleb DrCaleb:

PublicAnimalNo9 PublicAnimalNo9:

I was being facetious with my last comment DC

I know man. I was just expanding on a preconception that I think many people may hold. 'Infinite' is sometimes a hard concept. If you ever think I'm being too serious, look at my avatar.

Although I do have a problem with infinity, I have an even bigger problem with a finite universe or time. Even though the universe is 'this' big, it just doesn't end at a wall. And time... it's hard for me to imagine that time just started and that someday, it will end.

[Zipperfish]

Khar Khar:

Hmm, apologies, Zipperfish, I inferred from your "not too enamoured" mention that your viewpoint differred from mine in that regard. Remember that we see effects on other things from Dark Matter not only on worlds and other cosmological entities, but also in background radiation.

However, I think it's great you brought this up, because it's true there are many alternative theories. Many quantum gravity (those who watch The Big Bang Theory, Sheldon, Leonard and Leslie all do research in this field) models exist which do in part compete with the concept of Dark Matter. The first two, Sheldon and Leonard, work in what is called M-theory, or superstring theory. Leslie, on the other hand, works on the competing theory of loop quantum gravity. Both of these theories are FAR more ambitious than what we've been talking about here since they are researching a comprehensive theory of the function of natural forces un the universe. This stuff is at the very edge of modern study, and are only part of alternative theories. It's worth keeping in mind that these theories don't necessarily remove the need for Dark Matter, but rather postulate alternatives for the base theories at this time. Experimental evidence simply doesn't exist to the degree to dismiss other theories in favour of these ones. The math works out beautifully in many of these models, but there isn't the experimental evidence to back it up.

Simply put, there is a very real possibility we are wrong about gravity. There has been research which indicates that the gravitational constant may not be so constant, for example. This is one of the reasons why I am happy with the existence of Dark Matter, since it's very existence caused people to question the foundations of other theories. While there certainly are alternatives, however, we continue to explain these unknown powers through the term "Dark Matter" even if it may be misleading as to the depth of research being conducted in various subfields in Physics, since it's the best way to say "there's something there we can't entirely explain." It's one of those fun things like how "theory" in science means something different than "theory" in mainstream use, and how "agnostic" can have different meanings inferred if used in differing contexts.

There is a bit of a difference between the Many Worlds and chaotic inflation theories. While both metaverse models, Many Worlds is based on the idea that an endless series of universes exist which cover every concievable difference from each other's. Chaotic inflation has more to do with an endless series of big bangs creating entirely new universes. String theorists have their own special setup, but they also have 11 dimensions and interpret it all with 1 dimensional strings on a 2 dimensional medium, so let's not go in there because it makes my head ache just thinking about it. The difference between the first two is that one lies in probability space, and the other in regular spacetime.

In fact, metaverse theories are broken down into a taxonomy, much like evolutionary theory has trees. Level I and Level II are both based on chaotic inflationary theory. Level III is based on Many Worlds theory, and is similar to Level I. Level IV is the theory of everything. There is no Level V.

Well, I'll defer to you, since you're clearly more up to speed on the issue. I'm a little older and slower now, though there was a time I tried to stay on top of these things. I'm still interested, but just can't keep up anymore.

I agree 100% about gravity. Why does gravity only attract? Where is teh graviton? By far the most fascinating debate in physics for the last hundred years, INHO. Funny, I saw a global warming "denier" on TV the other day--can't recall who--who was saying that global warming was just a "theory." The interviewer responded "Well isn't everything a theory." The response was "No, not gravity. Gravity is the law!"

[Zipperfish]

raydan raydan:

DrCaleb DrCaleb:

PublicAnimalNo9 PublicAnimalNo9:

I was being facetious with my last comment DC

I know man. I was just expanding on a preconception that I think many people may hold. 'Infinite' is sometimes a hard concept. If you ever think I'm being too serious, look at my avatar.

Although I do have a problem with infinity, I have an even bigger problem with a finite universe or time. Even though the universe is 'this' big, it just doesn't end at a wall. And time... it's hard for me to imagine that time just started and that someday, it will end.

I have some good advice for you based on hard experience: Never think thoughts like these on mushrooms.