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Rethinking the origins of the universe

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Re: Rethinking the origins of the universe

#91
post #84

Earlier quoted context omitted.

If the spacetime is static, then yes, the trajectory of a light beam (or anything else) is reversible. The question you pose is an excellent one and is one of the reasons that many physicists believed that black holes could not exist after Karl Schwarzschild discovered the Schwarzschild metric that describes spacetime around a spherically symmetric black hole. So what happens if you direct a beam of light radially in…

You have this backwards. To a distant observer, light going into a black hole is red-shifted, not blue-shifted. If this were not the case, sending even a single photon into a black hole would produce infinite energy.

No, any photons that are emitted from matter close to the event horizon and travel toward the distant observer will be redshifted. Photons falling into the potential well of the black hole will be blueshifted. Of course, the distant observer is not able to directly detect photons falling into the black hole because he is far away from it. All he can do is calculate what he would expect the energy of the photons to be. This calculation gives an infinite energy as the photon approaches the event horizon, but it's not a "real" energy, so the black hole doesn't gain an infinite amount of energy.

An analogous effect occurs for an observer stationed at rest, hovering above the event horizon. Such an observer will observe the photons from afar to be blueshifed in agreement with the distant observer. Moreover, as this stationary observer gets closer and closer to the event horizon, the photons will be blueshifted to infinitely large energies.

Re: Rethinking the origins of the universe

#92
post #79

"from Star Trek to Hollywood" So... Hollywood? Star Trek wasn't filmed on location - Desilu and Paramount were both located in Hollywood. Not that this, y'know, matters - just found it amusing.

Filming Star Trek on location would have been pretty difficult, I'd imagine.

Well San Francisco, Cape Canaveral, and New York City figure in various episodes and movies. (Just off the top of my head.)

Re: Rethinking the origins of the universe

#93
related tidbit:

http://en.wikipedia.org/wiki/Black_hole#Evaporation

"A stellar black hole of one solar mass has a Hawking temperature of about 100 nanokelvins. This is far less than the 2.7 K temperature of the cosmic microwave background radiation. Stellar-mass or larger black holes receive more mass from the cosmic microwave background than they emit through Hawking radiation and thus will grow instead of shrink. "

Re: Rethinking the origins of the universe

#94
post #39

Ethan Siegel just posted a detailed response to this. https://medium.com/starts-with-a-bang/yes-virginia-black-hol...

That was written in February (how could you miss this? it's literally the very first thing at the top of the page) and doesn't mention either of this paper's authors. The article discusses a closely related but nevertheless quite different topic.

Was directed there from his Twitter feed where he seems to offer it as a response.

"There's been a story going around that it's been proven that black holes don't exist.

Yes, they do. "

https://twitter.com/StartsWithABang/status/51488524891693875...

Edit: Re-reading my original comment I see my choice of words was poor.

Re: Rethinking the origins of the universe

#95
post #71

Earlier quoted context omitted.

> 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…

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 they are also not hothouse orchids.

> They're humans with imaginations, beliefs, agendas, and egos, guided (hopefully) by a methodology that leads to discovery.

You have left the topic of science. The reason science exists is precisely because people are the way you describe them. Science is meant to be a counterpoint to natural human instincts, beliefs, passions, and other logical failings.

> I think belief is what drives science, and it's not all that bad of a thing.

You're now confusing science with religion. In religion, you let sincere feelings guide you to a conclusion. In science, you let logic guide you to a conclusion.

In religion, something is true until evidence proves it false. In science, something is false until evidence proves it true -- exactly the opposite.

Much of scientific discipline is meant to guard against what we believe is true or want to be true. Experimental and control groups, the classic double-blinding precautions in human studies -- all are meant to minimize the corrosive, undermining influence of our beliefs.

The perfect religious follower is guided by belief, hoping only that his work reflects his passion. The perfect scientist doesn't care what conclusion his work comes to, hoping only that it reflects reality to the best of his ability.

Belief and science are in absolute opposition.

Re: Rethinking the origins of the universe

#98
post #82
post #60

Earlier quoted context omitted.

> In particular, black holes can exist as long as they've always existed ... This doesn't work in physics. If you say they can only exist if they've always existed, then you're obliged to say how they came into existence earlier -- the deep meaning of "always".

The article implies that since singularities can't come into existence now, there can't have been a singularity at the moment of the Big Bang, either. That sounds implausible. Lots of things that cannot possibly come into existence at the present time did exist at the moment of the Big Bang (and shortly afterward), because the conditions back then were so radically different from they are now. Perhaps the only singul…

> The article implies that since singularities can't come into existence now, there can't have been a singularity at the moment of the Big Bang, either.

Yes, that's true, but if the paper's thesis is correct, then there aren't any black holes or singularities at all, at any time. If the thesis is false, then there can be black holes at the universe's beginning, and they can form today, given the right conditions.

> Lots of things that cannot possibly come into existence at the present time did exist at the moment of the Big Bang (and shortly afterward), because the conditions back then were so radically different from they are now.

Not so different, and from a theoretical standpoint, they lie on a continuum from the present to the past. The condition of the universe as a whole has changed over time, but from the present we can mimic earlier conditions using high energies.

It is often said that one goal of accelerator technology is to move backward in time toward the Big Bang. As technology advances, as accelerator energies increase, we create conditions more like the conditions in the early universe. The ultimate hope is to create conditions as much as possible like the first few seconds of the universe's existence, to be able to see the genesis of present conditions and refine physical theory.

> Perhaps the only singularity that ever existed was the Universe at the moment of the Big Bang. After the One Singularity has blown itself apart, no other singularity can come into existence. I don't see any inconsistency in that scenario.

A physicist would immediately see the inconsistency in that. If the conditions of the Big Bang theory can exist in reality, then given the same conditions of temperature and pressure, we should be able to imitate an earlier reality on a small scale. That's what an accelerator is designed to be -- an imitation of nature at an earlier time.

Re: Rethinking the origins of the universe

#99
post #25

Earlier quoted context omitted.

> So instead of the "black hole" being massive, it could be that time is running fast! I would have put it the other way around. Time passes more slowly near large masses relative to other locations.

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. Perhaps that's what the parent was getting at?

> 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, reflecting the fact that time passes more slowly at earth's surface than it does on the moon. The other equivalent interpretation under GR is that the light loses energy climbing out of the gravitational field and is therefore red-shifted. One of the beauties of Einstein's theory is that, if you do the math using either assumption (slower time or lost energy), the result comes out the same.

The classic confirmation of GR conducted in 1919 during a solar eclipse showed that the paths taken by starlight near the temporarily blocked sun were curved toward the sun. This is consistent with the idea that time passes more slowly near the sun. Consider that a light beam a bit closer to the sun would have a longer transit time (because of slower time passage) than one farther away, which would have the effect of curving the stellar light wavefront toward the sun.

This article has some graphics and deeper explanations to assist in understanding these ideas:

http://arachnoid.com/relativity

Re: Rethinking the origins of the universe

#100
post #94

Earlier quoted context omitted.

That was written in February (how could you miss this? it's literally the very first thing at the top of the page) and doesn't mention either of this paper's authors. The article discusses a closely related but nevertheless quite different topic.

Was directed there from his Twitter feed where he seems to offer it as a response. "There's been a story going around that it's been proven that black holes don't exist. Yes, they do. " https://twitter.com/StartsWithABang/status/51488524891693875... Edit: Re-reading my original comment I see my choice of words was poor.

Perhaps he hasn't read the paper we're talking about :-)
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