# Inflation theory and monopoles

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#### PSB

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Ok, second ever question and please be gentle with me!&nbsp; I'm a lady totally new to all this and trying to get my head around so many new concepts.&nbsp; Have been reading a little about Inflation theory and I am somewhat confused as to whether the references to a flat universe mean literally, or&nbsp;are they are relating to the gravitational density in the universe - or is it both???&nbsp; I thought that&nbsp;you could travel from any given point in the universe, in any direction and for a&nbsp;similar distance etc in which case it would mean that&nbsp;universe&nbsp;is&nbsp;more of a constant shape.&nbsp; Or am I missing the point totally?&nbsp;&nbsp;Also, can anyone explain to me why there&nbsp;is the need for proof&nbsp;of magnetic monopoles at the earliest time of creation, even if none have ever&nbsp;been found?&nbsp; What was their point/ why are they so important?&nbsp; Thanks.&nbsp;&nbsp; <div class="Discussion_UserSignature"> </div>

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#### DrRocket

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Ok, second ever question and please be gentle with me!&nbsp; I'm a lady totally new to all this and trying to get my head around so many new concepts.&nbsp; Have been reading a little about Inflation theory and I am somewhat confused as to whether the references to a flat universe mean literally, or&nbsp;are they are relating to the gravitational density in the universe - or is it both???&nbsp; I thought that&nbsp;you could travel from any given point in the universe, in any direction and for a&nbsp;similar distance etc in which case it would mean that&nbsp;universe&nbsp;is&nbsp;more of a constant shape.&nbsp; Or am I missing the point totally?&nbsp;&nbsp;Also, can anyone explain to me why there&nbsp;is the need for proof&nbsp;of magnetic monopoles at the earliest time of creation, even if none have ever&nbsp;been found?&nbsp; What was their point/ why are they so important?&nbsp; Thanks.&nbsp;&nbsp; <br />Posted by PSB</DIV></p><p>I'm not quite sure what you are reading or exactly what the question is.&nbsp; However, if you are interested in the topic of inflation the one trustworthy book for a general audience is <em>The Inflationary Universe</em>by Alan Guth.</p><p>Flatness of the universe is a reference to the notion of curvature as used in differential geometry.&nbsp; Basically a flat universe is one in which the sum of the angles in a triangle is 180 degrees.&nbsp;&nbsp;There are several measures of curvature, but the on most often quoted is Gaussian,&nbsp;because it is a scalar.&nbsp; What actually&nbsp;is used to describe gravity is the Riemann curvature tensor, wihich is a bit more complicated to describe, but from which on can&nbsp;determine Gaussian curvature.&nbsp; The&nbsp;universe is thought to be fairly close to flat on the largest scale at this time, but can be highly curved locally.</p><p>Guth's book give a fairly thorough discussion of the monopole question, tied to Grand Unified Theories (GUTs) for elementary particles.&nbsp; You ought to understand that this is on the edge of what is known, if not a bit beyond.&nbsp; No one has ever actually detected a monopole.&nbsp; And GUTs are still speculative.&nbsp; A grand unified theory is a unification of the theory of the strong force (quantum chromodynamics) with the theory of the electromagnetic and weak force (the electroweak theory), and no complete GUTs have yet been found.&nbsp; Now, add to a GUTs, the need to explain gravity and what you have described is the so-called Theory of Everything, and we don't have one of those yet either.&nbsp; Nevertheless, cosmologists are forced to work with assumptions as to what such theories might say.&nbsp; Guth is one of the best of that breed, and is the inventor of inflationary theories.</p><p>As I understand it GUTS plus the standard Bib Bang models predict far too many magnetic monopoles.&nbsp; That is a red flag that something else needs to be put into the theory of the origins of the universe.&nbsp; Inflation is an attempt to explain that origin and must contend with the monopole problem.<br /></p> <div class="Discussion_UserSignature"> </div>

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#### PSB

##### Guest
<p>[Thanks for that.&nbsp; I have to admit that some I get&nbsp;and some I still don't.&nbsp;I am presently reading a book by Michio Kaku and GUTs are discussed, along with string theory, M-theory etc.&nbsp; But all the time questions, just so many questions...</p><p>QUOTE]I'm not quite sure what you are reading or exactly what the question is.&nbsp; However, if you are interested in the topic of inflation the one trustworthy book for a general audience is The Inflationary Universeby Alan Guth.Flatness of the universe is a reference to the notion of curvature as used in differential geometry.&nbsp; Basically a flat universe is one in which the sum of the angles in a triangle is 180 degrees.&nbsp;&nbsp;There are several measures of curvature, but the on most often quoted is Gaussian,&nbsp;because it is a scalar.&nbsp; What actually&nbsp;is used to describe gravity is the Riemann curvature tensor, wihich is a bit more complicated to describe, but from which on can&nbsp;determine Gaussian curvature.&nbsp; The&nbsp;universe is thought to be fairly close to flat on the largest scale at this time, but can be highly curved locally.Guth's book give a fairly thorough discussion of the monopole question, tied to Grand Unified Theories (GUTs) for elementary particles.&nbsp; You ought to understand that this is on the edge of what is known, if not a bit beyond.&nbsp; No one has ever actually detected a monopole.&nbsp; And GUTs are still speculative.&nbsp; A grand unified theory is a unification of the theory of the strong force (quantum chromodynamics) with the theory of the electromagnetic and weak force (the electroweak theory), and no complete GUTs have yet been found.&nbsp; Now, add to a GUTs, the need to explain gravity and what you have described is the so-called Theory of Everything, and we don't have one of those yet either.&nbsp; Nevertheless, cosmologists are forced to work with assumptions as to what such theories might say.&nbsp; Guth is one of the best of that breed, and is the inventor of inflationary theories.As I understand it GUTS plus the standard Bib Bang models predict far too many magnetic monopoles.&nbsp; That is a red flag that something else needs to be put into the theory of the origins of the universe.&nbsp; Inflation is an attempt to explain that origin and must contend with the monopole problem. <br />Posted by DrRocket[/QUOTE]<br /></p> <div class="Discussion_UserSignature"> </div>

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