4 ms·

[Edit: Never mind -- I completely misread the quote, as JumpCrisscross points out.] I stopped reading here: "But just over a decade ago, astronomers noticed t

[Edit: Never mind -- I completely misread the quote, as JumpCrisscross points out.] I stopped reading here: "But just over a decade ago, astronomers noticed that the most distant galaxies were accelerating away from us much faster than the ones nearby. In fact, the further they looked, the greater the acceleration seemed to be." This was, in fact, noticed in 1917 by Vesto Slipher, derived from General Relativity by Georges Lemaitre in 1927, and further confirmed by Edwin Hubble in 1929, when it became known as Hubble's Law.

twiceaday 13y ago
Perhaps he meant century?
- deleted 13y ago
  [deleted]
JumpCrisscross 13y ago
Hubble's Law said the velocity of distant galaxies was faster than that of nearer ones. It is only in 1998 that we discovered the universe's expansion is accelerating, i.e. that Hubble's "constant" is shifting. We found this out by very precisely measuring the brightness of a very specific type of supernova, a Type Ia supernova, which has a very consistent intrinsic brightness (about 5 billion times brighter than our Sun) allowing for distance measurements with an uncertainty of just 5%. This was a novel achievement, enough to merit the 2006 Shaw Prize in Astronomy.
- VladRussian2 13y ago
  somebody needs to update wikipedia then: >Current evidence suggests the expansion of the universe is accelerating (see Accelerating universe), meaning that for any given galaxy, the recession velocity dD/dt is increasing over time as the galaxy moves to greater and greater distances; however, the Hubble parameter is actually thought to be decreasing with time, meaning that if we were to look at some fixed distance D and watch a series of different galaxies pass that distance, later galaxies would pass that distance at a smaller velocity than earlier ones.[33]
fargolime 13y ago
Discovered in 1998, and explained in 2008 using generally accepted equations, at http://finbot.wordpress.com/2008/03/05/dark-energy-obviated/ http://finbot.wordpress.com/2008/03/05/dark-energy-obviated/ In short, if you launch a unpowered projectile upward at close to the speed of light, Einstein's prediction of gravitational time dilation (experimentally confirmed) in turn predicts that the projectile accelerates away from you, for as long as its velocity relative to you is close to the speed of light. (The ivory tower no longer considers ideas that source outside the tower, which explains why this idea is in a blog.)
- dTal 13y ago
  I can't pretend to understand relativity well enough to verify that blog post's maths, but one of the notes caught my eye: <quote> 2. Herein, as in most relativity texts, we ignore the travel time of light that prevents a remote event from being seen until after it has occurred. In principle a network of observers can be set up in locally inertial frames that momentarily co-move with the rocket, so that events can be detected by equipment right next to them, and the records subsequently compiled and analyzed. </quote> I could be reading that wrong, but the author seems to be suggesting that time's inherent inconsistency at relativistic speeds and distances can be mitigated with a "network of observers". I don't know if that's true, but "momentarily co-move with the rocket" sounds like it's ignoring an awful lot of relativistic acceleration of the measuring devices.
  - fargolime 13y ago
    The network of observers are moving inertially (i.e. unpowered, freely falling), moving with the rocket for only a moment, so they're not accelerating like the rocket is. That's how those observers can make good measurements, in that moment. For more info search for "momentarily comoving inertial frame" at http://math.ucr.edu/home/baez/physics/Relativity/SR/clock.html http://math.ucr.edu/home/baez/physics/Relativity/SR/clock.ht.... Each inertial clock can measure the passage of time accurately.
- pdonis 13y ago
  The math in this post is fine (since, as you note, it's just plugging in numbers to "generally accepted equations"), but it is "solving" the wrong problem: if you launch a unpowered projectile upward at close to the speed of light, Einstein's prediction of gravitational time dilation (experimentally confirmed) in turn predicts that the projectile accelerates away from you In other words, the "acceleration profile" produced by this model is: acceleration, then deceleration. But the "acceleration profile" that needs to be explained for our actual universe is deceleration, then acceleration: an apparent slowing down of the universe's expansion, followed by an apparent speeding up. There's no way to get that out of the blog post's model.
spacebe4time 13y ago
Hubble discovered that the universe is expanding. It took another 70 years to discover that the universe's expansion is accelerating and telescope named after Hubble was involved in this discovery. In fact 3 scientists who discovered it received Nobel Prize back in 2011. http://en.wikipedia.org/wiki/Accelerating_universe http://en.wikipedia.org/wiki/Accelerating_universe Reading comprehension is a good thing to have before starting throwing bombs out there.

twiceaday 13y ago

Perhaps he meant century?

deleted 13y ago
[deleted]

JumpCrisscross 13y ago

Hubble's Law said the velocity of distant galaxies was faster than that of nearer ones. It is only in 1998 that we discovered the universe's expansion is accelerating, i.e. that Hubble's "constant" is shifting. We found this out by very precisely measuring the brightness of a very specific type of supernova, a Type Ia supernova, which has a very consistent intrinsic brightness (about 5 billion times brighter than our Sun) allowing for distance measurements with an uncertainty of just 5%. This was a novel achievement, enough to merit the 2006 Shaw Prize in Astronomy.

VladRussian2 13y ago
somebody needs to update wikipedia then: >Current evidence suggests the expansion of the universe is accelerating (see Accelerating universe), meaning that for any given galaxy, the recession velocity dD/dt is increasing over time as the galaxy moves to greater and greater distances; however, the Hubble parameter is actually thought to be decreasing with time, meaning that if we were to look at some fixed distance D and watch a series of different galaxies pass that distance, later galaxies would pass that distance at a smaller velocity than earlier ones.[33]

fargolime 13y ago

Discovered in 1998, and explained in 2008 using generally accepted equations, at http://finbot.wordpress.com/2008/03/05/dark-energy-obviated/ http://finbot.wordpress.com/2008/03/05/dark-energy-obviated/ In short, if you launch a unpowered projectile upward at close to the speed of light, Einstein's prediction of gravitational time dilation (experimentally confirmed) in turn predicts that the projectile accelerates away from you, for as long as its velocity relative to you is close to the speed of light. (The ivory tower no longer considers ideas that source outside the tower, which explains why this idea is in a blog.)

dTal 13y ago
I can't pretend to understand relativity well enough to verify that blog post's maths, but one of the notes caught my eye: <quote> 2. Herein, as in most relativity texts, we ignore the travel time of light that prevents a remote event from being seen until after it has occurred. In principle a network of observers can be set up in locally inertial frames that momentarily co-move with the rocket, so that events can be detected by equipment right next to them, and the records subsequently compiled and analyzed. </quote> I could be reading that wrong, but the author seems to be suggesting that time's inherent inconsistency at relativistic speeds and distances can be mitigated with a "network of observers". I don't know if that's true, but "momentarily co-move with the rocket" sounds like it's ignoring an awful lot of relativistic acceleration of the measuring devices.
- fargolime 13y ago
  The network of observers are moving inertially (i.e. unpowered, freely falling), moving with the rocket for only a moment, so they're not accelerating like the rocket is. That's how those observers can make good measurements, in that moment. For more info search for "momentarily comoving inertial frame" at http://math.ucr.edu/home/baez/physics/Relativity/SR/clock.html http://math.ucr.edu/home/baez/physics/Relativity/SR/clock.ht.... Each inertial clock can measure the passage of time accurately.
pdonis 13y ago
The math in this post is fine (since, as you note, it's just plugging in numbers to "generally accepted equations"), but it is "solving" the wrong problem: if you launch a unpowered projectile upward at close to the speed of light, Einstein's prediction of gravitational time dilation (experimentally confirmed) in turn predicts that the projectile accelerates away from you In other words, the "acceleration profile" produced by this model is: acceleration, then deceleration. But the "acceleration profile" that needs to be explained for our actual universe is deceleration, then acceleration: an apparent slowing down of the universe's expansion, followed by an apparent speeding up. There's no way to get that out of the blog post's model.

spacebe4time 13y ago

Hubble discovered that the universe is expanding. It took another 70 years to discover that the universe's expansion is accelerating and telescope named after Hubble was involved in this discovery. In fact 3 scientists who discovered it received Nobel Prize back in 2011. http://en.wikipedia.org/wiki/Accelerating_universe http://en.wikipedia.org/wiki/Accelerating_universe Reading comprehension is a good thing to have before starting throwing bombs out there.