The expansion of space is conceptually different from other kinds of expansions and explosions that are seen in nature, and does not involve heat.
Without the objects themselves moving, space is somehow 'growing' in between them.
It is the metric which defines distance that is changing rather than objects moving in space. (The metric is a formula which converts coordinates of two points into distances).
Unlike the metric of space, the metric of space-time is non-Euclidean i.e. not just three dimensions and three coordinates, but four, to include time.
The non-Euclidean nature of space-time manifests itself by the fact that the distance between points with constant coordinates grows with time, rather than remaining constant.
In other words, in expanding space, distance is a dynamical quantity which changes with time.
Now, colour me smug! 😀
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How are they constant when they are not? Has this ever been verified with measurements?
Also, how is there a time delay for light "reaching" us when nothing can move faster? How did we get to our coordinates faster than the light from objects further back in time? Why have they not been observable the whole time since the big bang?
"Why have they not been observable the whole time since the big bang?"
See section 9.2 here:
https://people.ast.cam.ac.uk/~pettini/Intro Cosmology/Lecture09.pdf
See section 9.2 here:
https://people.ast.cam.ac.uk/~pettini/Intro Cosmology/Lecture09.pdf
That's five questions in a row, Pete! Be easy on me!
In answer to the first question, the coordinates remain constant, but the metric that calculates the distance between any two points is changing.
Now that's where the boffin mathematics come in, which neither you nor I are unlikely to ever understand!
In answer to the first question, the coordinates remain constant, but the metric that calculates the distance between any two points is changing.
Now that's where the boffin mathematics come in, which neither you nor I are unlikely to ever understand!
Are you saying an object will always appear to be located in exactly the same position even though expansion has changed it?
I recall Mohammed Ali talking about how fast he was. He said he could go into his bedroom at night, turn off the light switch, and be in bed before the room went dark.
Voyager - Fact Sheet
400 000V and 3000 000A huh?! So that's about enough to power a big-ish laser to restructure the entire solar system, melting one asteroid at a time.
Build it on Io and just aim it where you want stuff to happen.
Here is the link to all of the cosmology lectures rayma pointed to earlier
Index of /~pettini/Intro Cosmology
Index of /~pettini/Intro Cosmology
We know they are moving apart because of redshift. The one thing that is constant is the speed of light c. So if c is constant everywhere in the universe, but it redshifts more and more the further back (= further away) no matter what the direction we look, we can deduce that any two points (or any number separated by some distance) are moving apart.
As Galu explained way back, local gravitational action may act as a countervailing force - as for example between the Milky Way and Andromeda which are moving towards each other.
As I've said, the objects do not move - the distance between them simply gets bigger.
This concept trancends our everyday experience, and may only be apprecated from a mathematical standpoint.
Our understanding of space-time requires that what we see normally as 'space', 'time', and 'distance' are not absolutes, but are determined by a metric that can change.
The metric expansion of space is a feature of many solutions to the Einstein field equations of general relativity, the simplest of which allows for the distances in space to change with an evolving scale factor.
In an expanding space-time, the metric changes with time in a way that causes distances to appear larger at later times. This explains why galaxies that are more distant from us appear to be receding faster than galaxies that are closer to us (Hubble's Law).
The Juno mission, in conjunction with the Hisaki satellite and Keck observatory, has recently discovered that Jupiter's intense aurora is responsible for heating the entire planet’s upper atmosphere to surprisingly high temperatures.
Juno Joins Observatories to Solve "Energy Crisis" on Jupiter
Wonder if there’s simple life in Jupiter’s upper atmosphere? Carl Sagan hypothesized about this. I haven’t watched this but it might here
Carl Sagan's Cosmos: Life on Jupiter - YouTube
Carl Sagan's Cosmos: Life on Jupiter - YouTube
It only does that locally. 'The System' is the universe, and on that scale we still move toward entropy. But you can beat entropy locally and for a limited time without violating the big picture. We see it with life, we also see it for, like, solar systems. The order is limited in place and time (spacetime?).
Jan
Yes, agree Jan. At small scales you can ‘reverse’ it through the self organizing behavior of atoms and the tendency to form molecules.
Here is an article by Adam Reiss on the accelerating expansion of the universe
https://www.stsci.edu/~ariess/documents/Shaw Prize Lecture_web.pdf
(Reiss received the Nobel prize along with Perlmutter and Schmidt for their discovery)
https://www.stsci.edu/~ariess/documents/Shaw Prize Lecture_web.pdf
(Reiss received the Nobel prize along with Perlmutter and Schmidt for their discovery)
What I gather from the article is that very distant supernovae have revealed a point in time when the expansion of the universe changed from slowing down to speeding up.
This is significant as it suggests that the expansion of the universe has not always been speeding up and bolsters the argument for the existence of dark matter and dark energy.
Whether or not the expansion is slowing down or speeding up depends on a battle between the gravitational pull of matter (most of which is dark matter) and the gravitational push of dark energy. What counts in this battle is the relative density of each.
It is presently thought that the density of dark energy does not to change as the universe expands. Conversely, the density of matter is decreasing as the universe expands.
Currently the density of dark energy is higher than that of matter, but in the distant past the density of matter should have been greater, so the expansion should have been slowing down then.
We know very little about dark energy, and the future of the universe hangs in the balance should the density of dark energy prove to change with time.
Yes - looks like the crossover point was the 7-9 billion yrs ago that I mentioned earlier.
The next few yrs in cosmology are going to be interesting that’s for sure.
Einstein’s Lambda afaik did not predict an acceleration of the expansion of the universe, so indeed something mysterious is out there!
🙂
The next few yrs in cosmology are going to be interesting that’s for sure.
Einstein’s Lambda afaik did not predict an acceleration of the expansion of the universe, so indeed something mysterious is out there!
🙂
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