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Rethinking the origins of the universe

unc.edu

121–130 of 141 posts

Re: Rethinking the origins of the universe

#121
post #99

Earlier quoted context omitted.

> FWIW, it's always been easier for me to think of it as 'moving' more quickly along the time axis - which would appear slowed down to someone farther away from the source of the gravity. In reality, it's the other way around. At the bottom of a gravity well, time passes more slowly. An astronaut on the moon observing a laser beam from earth's surface would see it as red-shifted compared to a local reference, reflect…

It's not the other way around. If you're deep in a gravity well, you observe physical processes happening outside that well to go along more quickly, not more slowly. And the reverse is true if you are outside a gravity well, observing something in it. Take some observer, Alice, far away from a massive body, who sees some process occurring near it take one second to complete. A second observer, Bob, nearer to the mas…

> It's not the other way around.

In your earlier post, you didn't clarify which observer was seeing which time pass more quickly, and where. In this post, you do -- sort of.

> Bob, nearer to the massive body, will see the same process take 1 - ε seconds to complete ...

If Bob and the process being observed are in the same frame of reference, Bob will see the process require a "normal" amount of time, i.e. a time consistent with classical physics. Alice will see Bob's process require more time on her clock, from her perspective. Bob, in the gravity well, will see Alice's time appear to be passing more quickly compared to his own.

> In effect, Bob has passed through one second of (Alice) time in only 1 - ε seconds of (local, to Bob) time.

This way of describing it is confusing. Here you are saying that Bob's experience of time is equal to Alice's time minus ε, when it's the reverse -- Bob sees Alice's time passing at 1 - ε, while his own time passes at a "normal" rate. It's a matter of how one describes it, because I suspect you understand how this works, the only problem is the prose.

> That's what I mean when I say "pass through time / move along the time axis more quickly".

Again, it's a matter of how one chooses to describe it, and it only proves the advantage of mathematics as a language. If we were discussing SR instead of GR, I would want to say, about the time experienced by (A)lice and (B)ob if (B)ob is moving at velocity v:

A = B / √(1-v^2/c^2)

B = A √(1-v^2/c^2)

In other words, Bob's time is slowed relative to Alice's time, as observed from Alice's frame of reference. The above two equations are only valid as written if Alice's time is compared to Bob's time after Bob completes his journey and brings his clock into Alice's frame of reference.

Re: Rethinking the origins of the universe

#122
post #62

If I understand correctly, black holes do not play a large role in our model of the origins of the universe. So this doesn't (directly) lead to "rethinking the origins of the universe". Does this work call the big bang into question (or even our current models of the big bang)? Or is it just details like galaxy formation that it makes us rethink? Another question: Something very massive and very small is at the cente…

> If I understand correctly, black holes do not play a large role in our model of the origins of the universe. So this doesn't (directly) lead to "rethinking the origins of the universe". But it does, because one hypothesis about the Big Bang is that it commenced from conditions identical to a black hole's singularity. So our understanding of black holes is critical to at least one idea about the universe's beginning…

I disagree completely. This calculation is about the formation of a black hole from a collapsing star. There is no theory stating that the singularity of which the big bang is theorized to expand from was brought into existence from a collapsing star.

Any theory about causes of that initial singularity are basically just conjecture at this point. My understand is that some of these high dimensional theories of quantum gravity postulate colliding 'membranes' and things but they are still very much in development and this calculation does nothing to further those theories along.

Another way I was thinking about it is that the initial singularity and creation of the universe is probably more a result of large scale, topological dynamics where this paper is concerned with more local, geometric dynamics. That's my own conjecture, there. :)

Re: Rethinking the origins of the universe

#123
post #12
post #11

What many people seem to overlook is that gravity is linked to time (space time)! So instead of the "black hole" being massive, it could be that time is running fast!

interesting any reference/publications on this?

When astronomers measure the mass of the black hole, they simply measure the acceleration of nearby stars, using newton's formula. They might use fancy words, but the math is very basic.

Now, if time ran faster, like if you made the measurements while accidentally having the video speed in fast forward. The stars would accelerate faster, and you would get a higher mass.

Re: Rethinking the origins of the universe

#124
post #62

Earlier quoted context omitted.

> If I understand correctly, black holes do not play a large role in our model of the origins of the universe. So this doesn't (directly) lead to "rethinking the origins of the universe". But it does, because one hypothesis about the Big Bang is that it commenced from conditions identical to a black hole's singularity. So our understanding of black holes is critical to at least one idea about the universe's beginning…

I disagree completely. This calculation is about the formation of a black hole from a collapsing star. There is no theory stating that the singularity of which the big bang is theorized to expand from was brought into existence from a collapsing star. Any theory about causes of that initial singularity are basically just conjecture at this point. My understand is that some of these high dimensional theories of quantu…

> There is no theory stating that the singularity of which the big bang is theorized to expand from was brought into existence from a collapsing star.

Not an issue, only that a singularity can exist, and therefore might come into being in the present.

If in a consistent physical theory we grant the reality of a singularity arising from very high matter density, then this narrows the range of possibilities for their nonexistence in the present.

So we have conventional densities easily explained by current theory, and we have the possibility of a singularity as an endpoint of increasing matter density, which narrows the discussion to the means whereby a mass might collapse past the critical density. I'm just saying this increases the burden on those who try to argue that the transition isn't possible. Especially given the absence of evidence in favor of, and plenty of evidence against, the stated thesis.

Re: Rethinking the origins of the universe

#125
post #117

Earlier quoted context omitted.

> [that it's naive to say that science doesn't turn on belief] depends entirely on what we mean when we say "science". Or it depends on what we mean when we say believe. The weight lying on "science" does form a conceptual framework that completely ignores the notion of something beyond our reach, although it inarguably is the driving force behind science. > In religion, something is true until evidence proves it fal…

> The weight lying on "science" does form a conceptual framework that completely ignores the notion of something beyond our reach, although it inarguably is the driving force behind science. Yes, but an idea doesn't become a matter of interest to science until it comes within our reach, in the sense of being observable in a way that forces different, similarly equipped observers to the same conclusion (the scientific…

I agree with your co-commentator, everything is subjective and we just take some things for granted so much that we take them as truth.

Seems i was wrong calling it inarguable, in fact i like to argue back and forth a lot.

> observable in a way that forces different, similarly equipped observers to the same conclusion (the scientific meaning of "objective").

no, that's still subjectivity, you just shifted the goal post. That kind of subjectivity might be your threshold for accepting some cognition as close enough to your supposition of objectivity, but it still requires trust on an individual level.

> an interesting question, but not really about science. Science concerns itself only with things that can be reduced to empirical observation, not belief.

Specifically by including subjectivity through empiricism, you in fact beget belief. I.e. measurements have an inherit uncertainty and you do what you can to reduce it.

> but the basic scientific precept is the null hypothesis, the idea that things without evidence are assumed to be false

You seem to fall for the fallacy of negated implication. My best guess is, the Null Hypothesis really states that evidence implies reality.

Or as my teacher put it, just because it didn't rain, the street doesn't have to be dry. It's hard to explain and I'm tired, sorry. I often fall for it, too.

Re: Rethinking the origins of the universe

#126
post #50

Earlier quoted context omitted.

I imagine that the metaphor "black hole" will be here for a while. After all, we still use the term "big bang" for the 'first moment' of the creation of the universe, even though the "Big Bang Theory" isn't generally believed any longer.

Erm, the big bang theory is still the best theory for the history of the universe.

No- it was replace by the inflationary theory long ago. They are different. You've kind of proved my point.

Re: Rethinking the origins of the universe

#127
post #71
post #50

Earlier quoted context omitted.

I imagine that the metaphor "black hole" will be here for a while. After all, we still use the term "big bang" for the 'first moment' of the creation of the universe, even though the "Big Bang Theory" isn't generally believed any longer.

> even though the "Big Bang Theory" isn't generally believed any longer. Really? Given that science doesn't turn on belief but evidence, still, the Big Bang remains the best explanation for existing evidence. It's the prevailing cosmological theory of the universe' beginnings. Like all scientific theories, it's subject to replacement as new evidence appears and as new theories are crafted, but it's a good match at th…

Big Bang remains the best explanation for existing evidence

No. The universe is too smooth for the Big Bang theory. It has been supplanted by the Inflationary theory.

Re: Rethinking the origins of the universe

#128
post #95

Earlier quoted context omitted.

I think it's a bit naive to say that science doesn't turn on belief. Scientist aren't robots, mechanically and dispassionately ingesting evidence and spitting out theory. They're humans with imaginations, beliefs, agendas, and egos, guided (hopefully) by a methodology that leads to discovery. I think belief is what drives science, and it's not all that bad of a thing.

> I think it's a bit naive to say that science doesn't turn on belief. That depends entirely on what we mean when we say "science". If by "science" we mean as defined and as practiced when it's done right, then no, belief plays no part -- it can't. If it did, it wouldn't be science. > Scientist aren't robots, mechanically and dispassionately ingesting evidence and spitting out theory. Scientists aren't robots, but th…

I'm not confusing science with religion. You might be describing something close to science in some ideal but certainly not what it looks like in reality. In reality, we don't have perfect experiments or evidence, and scientists have to draw conclusions based on interpretations of data. Like it or not, a lot of human factors come into play there. Even more so when the subjects themselves are human. If you want to rule out everything where there's a strong human, non-mechanical element from the world of science, then there's very little science going on to talk about.

Before we have advancement of theory, we have to have inspired hypothesis, and for that, we need imagination. If it weren't so, we wouldn't need great minds to propel us forward. While I agree that science promotes confrontation of bias, I don't think it serves any useful purpose to pretend that science actually happens in a clean room.

Re: Rethinking the origins of the universe

#129

This paper claims that black holes can't come into existence, which is subtly different from claiming that they cannot exist. In particular, black holes can exist as long as they've always existed – it's just that new ones can't come into existence. Maybe the universe just has a fixed number of singularities. [I am not a physicist – this just struck me as an inaccurate implication in the article.]

I agree that it seems as if the article is a bit overzealous as to the implications of this work (claiming singularities cannot exist, in particular the one from which the big bang expanded). But, your idea that something has "always existed" in a universe that hasn't "always existed" doesn't seem plausible. The author's claim that the big bang theory is now invalid because of this calculation of energy loss of a col…

You're experiencing cognitive bias.

If it is presumptuous to present calculations that may invalidate a _theory_ based on assumptions, then it is also presumptuous to disregard such calculations and state that the _theory_ itself is automagically correct, just because the assumptions are untouchable.

A bold assertion indeed.

Re: Rethinking the origins of the universe

#130
post #118
post #108

Earlier quoted context omitted.

No, the article only claims that a singularity cannot arise from a collapsing blob of matter. We have no evidence that the singularity that existed at the moment of the Big Bang was the result of a collapsing blob of matter. Therefore, we have no reason to think that it could not have occurred. In fact, it might not even make sense to think of that initial singularity as the result of anything at all, since causality…

> No, the article only claims that a singularity cannot arise from a collapsing blob of matter. If true, it calls into question the existence of the initial singularity thought to precede the Big Bang. The alternative -- that the working of physical theories depends on circumstances -- isn't a very good one. People sometimes hypothesize that this universe arose as a fluctuation in some other universe. For this kind o…

I'm not advocating the idea that the laws of physics depend on circumstances. I'm just pointing out that similar processes may have vastly different consequences, even according to the same theory, given vastly different environment variables (as evidenced by the ongoing Bash fiasco).

For example, we know that things tend to behave weirdly at quantum scales. It that because the usual laws of physics do not apply at quantum scales? No, our best theories should be able to explain why the scale makes such differences, and therefore accurately predict phenomena at every scale, both large and small.

Likewise, there would be nothing wrong with singularities occurring under some circumstances and not under others, as long as we can come up with a compelling theory to explain how the different circumstances affect the outcome.

That's the kind of theory we should try to come up with. Not hasty generalizations based only on limited observation of familiar circumstances. I'm not saying we will be successful, but it would be a mistake not to try.

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