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Post by theropod on May 22, 2015 1:46:36 GMT 5
The universe expanding manifests in distances within it becoming larger. Becoming larger doesn’t mean to displace any additional empty space, because it is space itself that is becoming larger along with it (and that’s what can be measured, stuff is simply drifting apart at a certain speed, due to inertia).
Since everything that is is by definition part of the universe, there cannot be anything beyond it.
Also, these two sentences from the opening post really don’t make any sense: "Personally, I like to think of it as infinite, so this there would be nothing beyond it. But if that is an unreasonable thought and something was beyond our universe, personally I would support the idea of there being absolutely nothing, as it is still growing."
because nothing=nothing while something≠nothing
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drone
Junior Member Rank 1
Posts: 53 
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Post by drone on May 22, 2015 17:01:51 GMT 5
Just a question, if the universe is everything, how can people say it expands? New matter is constantly being created? This counts as expanding. |
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Post by creature386 on May 22, 2015 19:41:45 GMT 5
Matter cannot be created nor destroyed. I like theropod's explanation better. Following it, the expansion process would not be something observable from "outside", but only through increasing distances between two objects.
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Post by theropod on May 22, 2015 19:56:45 GMT 5
There simply is no "outside", so that whole component is removed from the process. But there is observable evidence on the inside.
Matter can actually be created and destroyed tough. Think of E=mc², it’s the basis for powering our sun, as well as nuclear reactors.
Also, a sufficiently energized (i.e. the frequency is high enough) photon can form a particle-antiparticle pair when interacting with an atom. The reverse is also possible (particle-antiparticle pairs anahiliting themselves and forming photons).
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Post by creature386 on May 22, 2015 20:42:32 GMT 5
I know, that's why I used the quotation marks.
And thanks for the correction on matter. I still think that the creation of new matter in the expansion process is a bit flawed because matter (by definition) has mass and it is believed that the initial singularity had the mass of the universe (unless I misconstruct something again).
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Post by theropod on May 22, 2015 22:52:40 GMT 5
I don’t actually think the expansion of the universe includes the creation of new matter (matter gets created and destroyed all the time, so the total amount could have stayed the same), but I was basically too lazy to read and understand it properly, what I do know is that galaxies are drifting apart, as proven by the optical doppler effect.
Note that mass itself is not actually a conserved quantity (only mass+energy is), even tough baryonic and leptonic numbers are (antiparticles are counted as a negative, that’s apparently why my above example still works photon of sufficient energy→Proton[+1]+Antiproton[-1]=0).
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Post by creature386 on May 22, 2015 23:44:50 GMT 5
May I ask you for you definition of matter? When I said "Matter cannot be created nor destroyed.", I included energy under "matter", but after your response, I stopped doing so. Do you know any definition of matter to work with?
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Post by theropod on May 23, 2015 1:01:12 GMT 5
Oh, then that makes sense, energy really cannot be created or destroyed (in that case including its equivalent, mass). I thought you didn’t because you wrote the matter has mass-part, which is sort of what I had in mind too (i.e. matter being particles that have a rest mass, as opposed to massless ones).
Apparently defining matter is a bit of a problem. Forget what I wrote about conservation, it doesn’t quite hit the nail. Mass remains conserved through special relativity (increase the energy of a particle and you also increase its mass, ), so while matter can be converted into energy, mass doesn’t change. What I wrote only applies to the mass at rest (so maybe that could make for a working definition of matter).
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Post by creature386 on May 23, 2015 1:14:03 GMT 5
Note that my "matter has mass" stuff came after my "matter cannot be created nor destroyed part". It is a definition I found when quickly looking it up on wiki.
Anyway, as matter is (depending on the situation) a replaceable term, we probably should simply replace it.
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