Physics Help Forum Question about simplifying physics equations!?

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 Mar 9th 2013, 05:43 PM #1 Junior Member     Join Date: Feb 2013 Posts: 25 Question about simplifying physics equations!? Let's say that we had some equation in physics that was v(m+c)/v, which isn't real I am just using it, would you be able to simplify it to m+c? You shouldn't be able to because v for velocity has a possibility of being 0, correct? You can't simplify if you would be cancelling out a variable that could be zero, is this true? __________________ “Not only is the universe stranger than we think, it is stranger than we can think.” ― Werner Heisenberg
Mar 9th 2013, 06:58 PM   #2
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 Originally Posted by muon321 Let's say that we had some equation in physics that was v(m+c)/v, which isn't real I am just using it, would you be able to simplify it to m+c? You shouldn't be able to because v for velocity has a possibility of being 0, correct? You can't simplify if you would be cancelling out a variable that could be zero, is this true?
You are right on both counts. If you cancel v/v, you must specifically state that you are excluding the case v=0. Or you can take the limit as v-->0. The limit exists even if the function does not.

As a physicist, I tend to be a little careless about such cancellation - till a mathematical colleague corrects me!
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 Sep 24th 2013, 08:26 AM #3 Senior Member     Join Date: Aug 2013 Location: Under a bridge, Tampa, Florida USA Posts: 157 Bravo!!! I believe the science of physics has become accustomed to modifying things to make theories work easily! The latest example is here... http://www.nobelprize.org/nobel_priz...011/press.html Why should this measured expansion have a threshold, or a shape other than a cone? Is it just to preserve the theory of the "Big Bang"? Perhaps we should take the initiative of re-examining the "Big Bang" instead of warping the whole universe! While we are at it, what about the strong and weak nuclear forces... __________________ Deception is a complex concept which the human mind is unable to resolve...
Sep 24th 2013, 09:55 AM   #4

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 Originally Posted by Troll I believe the science of physics has become accustomed to modifying things to make theories work easily! The latest example is here... http://www.nobelprize.org/nobel_priz...011/press.html Why should this measured expansion have a threshold, or a shape other than a cone? Is it just to preserve the theory of the "Big Bang"? Perhaps we should take the initiative of re-examining the "Big Bang" instead of warping the whole universe! While we are at it, what about the strong and weak nuclear forces...
(sighs)
 ...warping the whole Universe
What?

As to the nuclear forces they do not have any effect on the Universe at this point...the scales of the interactions are too small. If you are referring to these forces when the Universe was almost infinitesimally small then yes, we have to include these and we do. Look up GUTs. Even if a GUT seems too complicated to do anything with I can assure you that the geometries they represent are a major source of simplification.

And of course the BB is under scrutiny! But what you are probably objecting to is the "cobbling" up of several different theories working together to give us what we call the "Standard Model." (Of which the BB is included.) When we have a TOE we might be able to explain everything in one nice package, but we are far from having one. So we have to put several pieces together for now.

-Dan
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Sep 24th 2013, 10:01 AM   #5
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 Originally Posted by topsquark (sighs) As to the nuclear forces they do not have any effect on the Universe at this point... -Dan
That is rather odd isn't it? Every other force in nature has an influence on the universe that extends to infinity via the inverse square... so why are the nuclear forces so special?
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Sep 24th 2013, 10:04 AM   #6
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 Originally Posted by topsquark (sighs) When we have a TOE we might be able to explain everything in one nice package, but we are far from having one. -Dan
My thinking is that TOE begins with an elementary "particle", perhaps this seems backwards, perhaps however we can work both ends towards the middle?
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Sep 25th 2013, 11:02 AM   #7

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 Originally Posted by Troll That is rather odd isn't it? Every other force in nature has an influence on the universe that extends to infinity via the inverse square... so why are the nuclear forces so special?
It's simply their nature and the nature of the particles that carry them. The strong force has a limited radius because of something called "confinement." This comes in two parts: The first is that strong particles can only be "free particles" when they are close together. (The effective range here is 10^(-15) m or so...no surprises that this is about the size of a nucleus.) The second is that particles with a "non-zero" color charge cannot be detected. Both of these keep the strong force from dominating the Universe. (It's much stronger than EM and waaaay stronger than gravity.)

As for the weak nuclear force, I suppose it could span long distances, but the vector bosons have a lifetime on the order of 10^(-25) s, so we won't be seeing them interact on a 10 m scale.

The difference between these two forces and gravity and EM? The photon mediates EM and has an infinite lifetime. As do gravitons. So they are the only two of the forces that make up the macroscopic features of the Universe.

 Originally Posted by Troll My thinking is that TOE begins with an elementary "particle", perhaps this seems backwards, perhaps however we can work both ends towards the middle?
A single particle? Dude. GUT's alone consist of 128 elementary particles (more depending on which GUT you are looking at.) I have no idea about a TOE except to say that it's going to be larger. I can't give you any simple reason why. It has to do with the symmetry group that the TOE is based on. So there isn't going to be any "master particle," with the possible exception of the singularity at 0 time. And that might not be a single particle either.

-Dan
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 Sep 27th 2013, 01:35 PM #8 Senior Member     Join Date: Apr 2008 Location: Bedford, England Posts: 668 The Elephant in the Room There is a story about some blind men describing an elephant by touch alone, one gets hold of the trunk and says the elephant is like a snake, another gets hold of a leg and says the elephant is like a tree, etc... Physicists get hold of pieces of reality and make up particles to match the particular bit they have got hold of. The full nature of reality however remains elusive.
Sep 27th 2013, 03:17 PM   #9

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 Originally Posted by MBW The full nature of reality however remains elusive.
But of course! As to the full nature of reality is concerned there is a simple thought that I have when I'm solving equations, especially the ones I have to work out with great difficulties:

The Universe doesn't solve differential equations. It just does what it does. When we truly understand the Universe we won't have to either.

-Dan
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 Oct 7th 2013, 08:34 AM #10 Senior Member     Join Date: Aug 2013 Location: Under a bridge, Tampa, Florida USA Posts: 157 Bravo! I was beginning to think you were a bunch of stale old farts stuck to what you have learned! I would like to propose a primary entity that is toroidal and expanding. At a single point this entity compresses time/space infinitely, at an infinite distance time/space is expanded infinitely, and in between the relationship between time and space is exponential. The interference pattern between such entities is what we perceive as matter. Comments welcome and math desired! __________________ Deception is a complex concept which the human mind is unable to resolve...

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