Airbrush Posted October 8, 2017 Posted October 8, 2017 (edited) 9 hours ago, scherado said: That might be called a probable definition. On what basis would one define the bounds of the universe using the word "probable?"...... "The Universe is all of space and time (spacetime) and its contents..." https://en.wikipedia.org/wiki/Universe How can all of that not be infinite? That is why I used a probable definition. "The Universe can be defined as everything that exists, everything that has existed, and everything that will exist.[21][22][23] According to our current understanding, the Universe consists of spacetime, forms of energy (including electromagnetic radiation and matter), and the physical laws that relate them. The Universe encompasses all of life, all of history, and some philosophers and scientists suggest that it even encompasses ideas such as mathematics and logic.[24][25][26] Edited October 8, 2017 by Airbrush
pzkpfw Posted October 8, 2017 Posted October 8, 2017 (edited) Why does it follow that "everything" is "infinite"? Edited October 8, 2017 by pzkpfw
Airbrush Posted October 8, 2017 Posted October 8, 2017 (edited) Good question! Because it is everything. How can "everything" not be infinite? What about all the space surrounding whatever is finite? Space exists. "[Universe] defined as everything that exists, everything that has existed, and everything that will exist...] https://en.wikipedia.org/wiki/Universe Edited October 8, 2017 by Airbrush
pzkpfw Posted October 8, 2017 Posted October 8, 2017 Yeah, I'm just not seeing how that follows. The "logic" seems to be: Everything is infinite. The Universe is Everything. Therefore the Universe is Infinite. ... which is pretty circular. What is it about "Everything" that makes it infinite?
Strange Posted October 8, 2017 Posted October 8, 2017 2 hours ago, Airbrush said: How can "everything" not be infinite? What if everything, all of space-time, has a finite volume (and a finite mass, finite number of atoms, etc.)?
Airbrush Posted October 8, 2017 Posted October 8, 2017 2 hours ago, Strange said: What if everything, all of space-time, has a finite volume (and a finite mass, finite number of atoms, etc.)? What is surrounding the finite volume? Space, and space is not nothing.
zapatos Posted October 9, 2017 Posted October 9, 2017 (edited) 27 minutes ago, Airbrush said: What is surrounding the finite volume? Space... And you know this how? Edited October 9, 2017 by zapatos
beecee Posted October 9, 2017 Posted October 9, 2017 42 minutes ago, Airbrush said: What is surrounding the finite volume? Space, and space is not nothing. Partly agree...the part where space is not nothing. But the BB itself was the evolution of space and time, (spacetime) "as we know it" We can only speculate about anything else.
Airbrush Posted October 9, 2017 Posted October 9, 2017 27 minutes ago, zapatos said: And you know this how? I don't know it. I am speculating using reasoning. There is no other way to discuss it. How can you imagine anything of finite size, with nothing beyond it? Space is not nothing.
zapatos Posted October 9, 2017 Posted October 9, 2017 11 minutes ago, Airbrush said: I am speculating using reasoning. No, you are speculating using incredulity. You are saying "I cannot imagine it so it must not be so". Quote How can you imagine anything of finite size, with nothing beyond it? By recognizing that there are things I don't know or comprehend.
Strange Posted October 9, 2017 Posted October 9, 2017 7 hours ago, Airbrush said: What is surrounding the finite volume? Space, and space is not nothing. If the universe is finite, it is still unbounded; i.e. There is nothing outside it. As a 2D analogy, consider the surface of a sphere (just the surface, this is a 2D analogy). That has a fixed measurable area but there is no edge of the world where you can look over the edge. If you go far enough in any direction you will eventually end up where you started.
Cosmo_Ken Posted October 15, 2017 Posted October 15, 2017 On 8/1/2017 at 3:38 PM, beecee said: As MigL has said the observable universe is certainly finite, and around 96 billion L/years in diameter. The WMAP probe showed the universe to be very nearly flat within small error bars, and that in the main points to an infinite universe, although a universe shaped like a torus which is also flat, is obviously finite. The other point to remember is the "flatness" as per WMAP did have error bars, albeit small, which in effect could mean that the flatness measured is simply an arc of a much larger closed universe. In any respect though the universe is pretty big or as I like saying [and have been taken to task over it] near infinite in extent and content. How can the universe be around 96 billion light-years in diameter, since it is supposed to be just over 13 billion years old, this would require the average expansion rate since the big bang of more than the speed of light, i.e. expanding at an average rate equal to the speed of light would result in a diameter of about 27 billion light-years, not 96???
Airbrush Posted October 15, 2017 Posted October 15, 2017 Space can expand faster than the speed of light. Matter cannot move through space faster than the speed of light.
Cosmo_Ken Posted October 15, 2017 Posted October 15, 2017 Has space expanded that much??? What rate of expansion of space has occurred as a function of time since the BB started? Is it still expanding?
Mordred Posted October 15, 2017 Posted October 15, 2017 Well in less than a second during inflation it expanded 60 e folds. Since then its expansion rate per Mpc has been slowing down. However due to quantity of Mpc. The rate of expansion of the overall volume is accelerating.
Strange Posted October 15, 2017 Posted October 15, 2017 (edited) Expansion is not a speed, it is a scaling effect so the speed with which two pints move apart depends how far apart they are. The current rate of expansion is about 70 km/s per megaparsec. https://www.space.com/25179-hubble-constant.html the most distant light took about 13.8 billion years to get here. The source was about 4.5 billion light years then but because space was expanding it had to travel an increasing distance, hence the travel time was so long. Now, that source is about 47 billion light years away. https://en.m.wikipedia.org/wiki/Observable_universe#Misconceptions_on_its_size Edited October 15, 2017 by Strange
Mordred Posted October 15, 2017 Posted October 15, 2017 (edited) Here, this is expansion history CMB forward including future expansion. The H_0/H_Z column is expansion rate today compared to then as a function of redshift [latex]{\small\begin{array}{|c|c|c|c|c|c|}\hline T_{Ho} (Gy) & T_{H\infty} (Gy) & S_{eq} & H_{0} & \Omega_\Lambda & \Omega_m\\ \hline 14.4&17.3&3400&67.9&0.693&0.307\\ \hline \end{array}}[/latex] [latex]{\small\begin{array}{|r|r|r|r|r|r|r|r|r|r|r|r|r|r|r|r|} \hline a=1/S&S&z&T (Gy)&R (Gly)&D_{now} (Gly)&D_{hor}(Gly)&D_{par}(Gly)&H/Ho \\ \hline 0.001&1090.000&1089.000&0.000373&0.000628&45.331596&0.056714&0.000856&22915.263\\ \hline 0.001&739.062&738.062&0.000713&0.001172&45.031283&0.083238&0.001668&12283.974\\ \hline 0.002&501.112&500.112&0.001342&0.002163&44.653685&0.122010&0.003214&6658.325\\ \hline 0.003&339.773&338.773&0.002496&0.003956&44.183524&0.178562&0.006124&3639.803\\ \hline 0.004&230.379&229.379&0.004601&0.007192&43.602350&0.260828&0.011554&2002.235\\ \hline 0.006&156.206&155.206&0.008416&0.013015&42.887747&0.380106&0.021616&1106.404\\ \hline 0.009&105.913&104.913&0.015309&0.023478&42.012463&0.552333&0.040144&613.344\\ \hline 0.014&71.813&70.813&0.027726&0.042257&40.943206&0.799715&0.074095&340.773\\ \hline 0.021&48.692&47.692&0.050056&0.075939&39.639382&1.152677&0.136056&189.626\\ \hline 0.030&33.015&32.015&0.090158&0.136321&38.051665&1.651928&0.248752&105.633\\ \hline 0.045&22.386&21.386&0.162117&0.244527&36.119894&2.350040&0.453165&58.889\\ \hline 0.066&15.178&14.178&0.291145&0.438335&33.771262&3.311204&0.823085&32.852\\ \hline 0.097&10.291&9.291&0.522342&0.785104&30.917756&4.606237&1.491191&18.342\\ \hline 0.143&6.978&5.978&0.936102&1.403692&27.454972&6.297233&2.695518&10.259\\ \hline 0.211&4.731&3.731&1.674119&2.496871&23.266389&8.402147&4.860753&5.767\\ \hline 0.312&3.208&2.208&2.977691&4.373615&18.247534&10.827382&8.733318&3.292\\ \hline 0.460&2.175&1.175&5.215425&7.334123&12.397762&13.279345&15.569626&1.963\\ \hline 0.678&1.475&0.475&8.789420&11.115281&6.042158&15.275613&27.272101&1.296\\ \hline 1.000&1.000&0.000&13.787206&14.399932&0.000000&16.472274&46.278944&1.000\\ \hline 1.468&0.681&-0.319&19.704190&16.201608&4.910267&16.992292&75.113899&0.889\\ \hline 2.154&0.464&-0.536&26.084608&16.928765&8.515267&17.174536&118.018864&0.851\\ \hline 3.162&0.316&-0.684&32.638034&17.180008&11.040250&17.224075&181.212698&0.838\\ \hline 4.642&0.215&-0.785&39.249711&17.261713&12.776339&17.261713&274.042078&0.834\\ \hline 6.813&0.147&-0.853&45.880114&17.287747&13.962589&17.287747&410.320588&0.833\\ \hline 10.000&0.100&-0.900&52.516301&17.296130&14.771503&17.296130&610.357404&0.833\\ \hline 14.678&0.068&-0.932&59.154549&17.298683&15.322788&17.298683&903.973904&0.832\\ \hline 21.544&0.046&-0.954&65.793394&17.299445&15.698407&17.299445&1334.944709&0.832\\ \hline 31.623&0.032&-0.968&72.432255&17.299812&15.954315&17.299812&1967.523376&0.832\\ \hline 46.416&0.022&-0.978&79.071348&17.299828&16.128669&17.299828&2896.022178&0.832\\ \hline 68.129&0.015&-0.985&85.710288&17.299959&16.247453&17.299959&4258.871858&0.832\\ \hline 100.000&0.010&-0.990&92.349407&17.299900&16.328381&17.299900&6259.261851&0.832\\ \hline \end{array}}[/latex] The S=1.000 column is today, you have the three horizons and age of universe with total radius. Edited October 15, 2017 by Mordred
Airbrush Posted October 15, 2017 Posted October 15, 2017 (edited) On 10/9/2017 at 0:03 AM, Strange said: If you go far enough in any direction you will eventually end up where you started. If traveling in a straight line, to end up where you started is a curved path. How can a straight line also be curved? Edited October 15, 2017 by Airbrush
Strange Posted October 15, 2017 Posted October 15, 2017 35 minutes ago, Airbrush said: If traveling in a straight line, to end up where you started is a curved path. How can a straight line also be curved? On the surface of the Earth, if you travelled in straight line you would end up where you started.
Airbrush Posted October 15, 2017 Posted October 15, 2017 (edited) Strictly speaking, if you traveled in a "straight" line on Earth, the path would be very slightly curved, not straight. A "straight" line on Earth would be a tangent that lifts off the Earth's surface. But I get it, the model is a 2D representation of 3D space, so the model is imperfect, but meant to convey a deeper meaning, which is totally beyond me. Edited October 15, 2017 by Airbrush
pzkpfw Posted October 15, 2017 Posted October 15, 2017 How about being in a spacecraft orbiting a planet? You don't feel any acceleration; so as far as you can (not) feel, you are travelling "straight". Yet to another observer, you are going in ellipses around that planet.
Strange Posted October 15, 2017 Posted October 15, 2017 1 hour ago, Airbrush said: Strictly speaking, if you traveled in a "straight" line on Earth, the path would be very slightly curved, not straight. A "straight" line on Earth would be a tangent that lifts off the Earth's surface. But I get it, the model is a 2D representation of 3D space, so the model is imperfect, but meant to convey a deeper meaning, which is totally beyond me. If we are talking about the surface of the Earth, then we are talking about a 2D model. Therefore the line is not curved (because the curvature you are seeing is in a third dimension which does not exist in the analogy). The equivalent of a straight line on the curved surface of the Earth or in curved space-time is called a geodesic. You can think of it as the shortest distance between two points in that coordinate system.
Mordred Posted October 15, 2017 Posted October 15, 2017 (edited) I have a far more complex way of thinking of geodesics. It is the sum of all infinitisimal deviations between two seperation points due to the local infinitisimal field interaction at each coordinate and immediate surrounding infinitisimals within infinitisimal causality units. Whats real fun is understanding and applying the above under lattice gauge treatments. Here is a thought experiment to understand local. "What is the radius of a field that can interact with a particle, bofore the particle moves " Now obviously the above has no easy answer, as numerous factors will need to be known. However it demonstrates the principle of local under motion and causality. Edited October 15, 2017 by Mordred
Strange Posted October 15, 2017 Posted October 15, 2017 30 minutes ago, Mordred said: I have a far more complex way of thinking of geodesics. because of course you do. 1
koti Posted October 15, 2017 Posted October 15, 2017 1 hour ago, Mordred said: I have a far more complex way of thinking of geodesics. It is the sum of all infinitisimal deviations between two seperation points due to the local infinitisimal field interaction at each coordinate and immediate surrounding infinitisimals within infinitisimal causality units. Whats real fun is understanding and applying the above under lattice gauge treatments. Here is a thought experiment to understand local. "What is the radius of a field that can interact with a particle, bofore the particle moves " Now obviously the above has no easy answer, as numerous factors will need to be known. However it demonstrates the principle of local under motion and causality. Ah the field interactions. Trying to read up on this whenever I find some time, I’m not doing a good job so far 1 hour ago, Strange said: because of course you do. One could think that Mordred is cocky if one did not know Mordred
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