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I have the good sense not to comment on matters I have not studied in depth. The only advantage of having people who do not follow this approach is that it keeps active hundreds of forums on many disciplinesSo.. any substantive response to the dark energy point while we are here?
Accelerating if the change in velocity with distance is non-linear.they all contribute to the observation that more distant objects appear to be receding more quickly-
not necessarily accelerating-
You should update your understanding of common fallacies. It would be absurd if it was fallacious to prefer expert consensus over uninformed opinion.Don't worry I forgive you! argument from authority is one of the most common fallacies and we have all been guilty of it at some point. I am old enough to remember science teachers who still looked to Hoyle as an authority on the steady state nature of the universe..
A repulsive force is the simplest explanation as, in the physics of GR, it just involves a positive cosmological constant, producing negative pressure vacuum energy which results in a repulsive gravitational field.There are several alternate theories, my original point was just that the same general observation of objects receding at greater speeds at greater distances doesn't require a repulsive force- positive gravity can do the same
Accelerating if the change in velocity with distance is non-linear.
You should update your understanding of common fallacies. It would be absurd if it was fallacious to prefer expert consensus over uninformed opinion.
A repulsive force is the simplest explanation as, in the physics of GR, it just involves a positive cosmological constant, producing negative pressure vacuum energy which results in a repulsive gravitational field.
Can you explain what you mean by 'positive gravity' and how it would produce the acceleration effect?
The point is to find the simplest explanation for the phenomenon. Galaxies are not automotive, distant ones typically have very small proper motion compared with their recession velocity. Accelerating expansion accounts for the red-shift observations and is supported by other measurements as previously described.You could use doppler shift to measure several cars, with a non linear differential in velocity over distance. This still would not tell you any cars are accelerating, just that they are travelling more quickly at further distances
That would depend which street you chose. In Buddhism, Hinduism, & Jainism, time and the universe are eternal. Other religions have a variety of origin myths, but when the choice is between origin or no origin, it's no surprise that large numbers claim 'origin' without any empirical knowledge of the universe. Expressions of uninformed belief are not what is generally meant by the 'the wisdom of the crowd'.intuitively absurd yet curiously useful- when the overwhelming majority of cosmologists favored static/ steady state models, the average man on the street could have told you there was a beginning- 'wisdom of the masses' some call it
He called it his 'biggest blunder' because he'd put it in to conform to a presumption of a static universe rather than evidence of such. Now we have evidence of accelerating expansion, it's a pragmatic candidate, but not the only one.That's the mistake Einstein made, using the gap in his math to 'discover' a new constant
As previously explained, there are no directly measured velocities either, just higher red-shifts.There is no directly measured acceleration, just higher velocities at greater distances
Can you explain how a gravitational collapse produces the appearance of accelerating expansion (rather than, say, a black hole)?positive/attractive gravity can, and would produce this same observation in itself- beginning with an initial collapse which is what the OP'er was speculating about
The point is to find the simplest explanation for the phenomenon.
That would depend which street you chose. In Buddhism, Hinduism, & Jainism, time and the universe are eternal. Other religions have a variety of origin myths, but when the choice is between origin or no origin, it's no surprise that large numbers claim 'origin' without any empirical knowledge of the universe. Expressions of uninformed belief are not what is generally meant by the 'the wisdom of the crowd'.
As previously explained, there are no directly measured velocities either, just higher red-shifts.
Can you explain how a gravitational collapse produces the appearance of accelerating expansion (rather than, say, a black hole)?
An 'entirely new' force is not necessary - as mentioned, gravity can do the job. But there is no problem with introducing a new force if that is what best explains the observations; the currently known forces are relatively recently identified and formulated as such.like one that does not require an entirely theoretical new energy force like dark energy?
Sure, but how is that relevant?And it depends on what we call an 'expert'Roger Federer has won 20 Grand Slams- I think we can all agree he is an expert at the game of tennis, and I would certainly value his advice on it
He predicted a big crunch given certain assumptions, which turned out not to hold. Hawking radiation is not expected to be detected as its intensity inversely proportional to the size of the black hole, and it has a thermal signature. We couldn't detect it for a black hole large enough for us to see even if there was no other radiation from outside the event horizon - of which there is usually vast quantities. It's generally accepted because it's a prediction of quantum mechanics at the event horizon.Stephen Hawking was considered an expert on cosmology- he predicted a 'Big Crunch' that time would reverse and we would literally crawl back into the womb- before this was debunked by some of the observations we are discussing- also Hawking radiation, which I don't think anyone ever found yet
Having said that he overcame enormous adversity, sold millions of books, and entertained and inspired millions of people- I'd say that's where his demonstrable expertise lay
Quite; but a Doppler effect fits the data and satisfies common abductive criteria better than other suggested explanations, just as accelerating expansion fits the data and satisfies common abductive criteria better than other suggested explanations.... that's true yes, the red shift could be caused by something else also...
There's nothing mysterious about it. Voyager 1 had a different trajectory from Voyager II, so gained sufficient momentum from gravitational slingshots to overtake it. The expansion of space has no effect within gravitationally bound systems such as our galaxy.For example- we were discussing the voyager probes/ interstellar space travel etc on another thread.
Voyager 1 is much further away than Voyager II and is also moving faster
Does this suggest it is moving faster because it is further away - being repelled by a mysterious force? or that it is simply further away because it is moving faster?
what sort of mysterious force caused it to be receding from/ defying our system's gravity even more quickly than voyager II?
Quite; but a Doppler effect fits the data and satisfies common abductive criteria better than other suggested explanations, just as accelerating expansion fits the data and satisfies common abductive criteria better than other suggested explanations.
There's nothing mysterious about it. Voyager 1 had a different trajectory from Voyager II, so gained sufficient momentum from gravitational slingshots to overtake it. The expansion of space has no effect within gravitationally bound systems such as our galaxy.
None of that explains how a large amount of mass collapsing under its own gravity could give the appearance of accelerating expansion.
It's not speculative because it's been tested by other observations (previously mentioned) which are consistent with that explanation.the acceleration is based in turn on the redshift- assuming it is doppler- i.e. the acceleration is a farther speculation
I know. But how does that explain how a large collection of mass collapsing under its own gravity gives the appearance of accelerating expansion?So it used attractive gravity to repel itself away from gravity- with no additional repelling force required
It's not speculative because it's been tested by other observations (previously mentioned) which are consistent with that explanation.
I know. But how does that explain how a large collection of mass collapsing under its own gravity gives the appearance of accelerating expansion?
If you don't know, just say so.
It is the expansion of space that is accelerating. The differences in the velocities of galaxies with distance are consistent with that.again the other observations may be interpreted to support the same observation- that more distant objects are receding more quickly, not that they are actually accelerating.
OK. I'll take that as a "don't know".Voyager and Saturn essentially 'collapsed' towards each other, contributing to their own separation velocity
It is the expansion of space that is accelerating. The differences in the velocities of galaxies with distance are consistent with that.
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OK. I'll take that as a "don't know".
I accept that the Voyager slingshot around Saturn doesn't explain how the apparent outward acceleration of the universe arises from its matter collapsing under its own gravity. You may remember being asked why that wouldn't result in a black hole.you don't accept that the probe got closer to Saturn, before it got further away?
I accept that the Voyager slingshot around Saturn doesn't explain how the apparent outward acceleration of the universe arises from its matter collapsing under its own gravity.
You may remember being asked why that wouldn't result in a black hole.
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