“You cannot escape the responsibility of tomorrow by evading it today.” -Abraham Lincoln
As you've come to expect, it's been another fantastic week of science here on Starts With A Bang!? There's a chance I'll be in Las Vegas next month for the official Star Trek convention, and in addition to all we're doing, there's a chance that there will be a new YouTube video series coming out that features me and the fusion of sci-fi/fantasy with science. Sounds fun? You bet it does! Also, for those of you in and around Portland, OR, join me at 2 PM at the Oregon Historical Society today to catch my talk on the Last Great American Eclipse. You won't want to miss it!
With all that said, here's what the last week has held in terms of our new stories:
- Could we save the Earth by migrating it away from the Sun? (for Ask Ethan),
- Discovery of a young, dead galaxy creates a huge puzzle for astronomers (for Mostly Mute Monday),
- How a solar eclipse first proved Einstein right,
- The Universe itself may be unnatural,
- Sorry, Donald Trump, it can't be infinity, and
- Is it possible to pull something out of a black hole?
With that out of the way, let's all enjoy the best of our comments of the week!
Without dark energy, the Universe wouldn't be accelerating. But there's no way to access that energy via any other particles in the Universe. Image credit: NASA & ESA.
From Pentcho Valev on the Universe's beginnings and dark energy: "You have vacuum full of energy, detectors in contact with this vacuum which register strange noise coming from all directions, and you conclude that the noise is not produced by the vacuum energy but comes from the miraculous beginning of space and time."
Yes, that is correct. Except, the way you've framed it indicates that you've misunderstood how everything about the physical Universe works. I'm happy to clear that up, but I want you to stay with me afterwards, too.
Yes, we have a vacuum that is full of energy, because we measure the zero-point energy of space thanks to the effect that such energy has on the Universe's expansion. That is the only way we detect this energy, the energy inherent to space itself, in a quantitative fashion. Everything is in contact with this vacuum only to the extent that everything exists in space, which is what "the vacuum" is: empty space. The detectors, then, that you're talking about, aren't detecting energy from the vacuum, but rather from the external Universe. How do we know? Because if you build a "shield" (i.e., a conductor) around your detector, the "strange noise" goes away. Because it's coming from an external source: the surface of last scattering from when the Universe was transitioning from an ionized plasma to a state full of neutral atoms. What you call strange noise is actually well-measured, quantified, well-defined, and simple: it's blackbody radiation redshifted by the expansion of the Universe.
With that established, I want to clarify something for you: I am happy, in these comments, to address whatever physical gaps you may have in your knowledge. Whatever you're curious about, or want to know more about, I'm happy to share my knowledge -- as a professional astrophysicist and cosmologist -- with you. If you have questions about facts, my opinions, or anything else, I'm happy to respond.
But I am most definitely not interested in your alternative, pet theories to well-established theories. I am also not interested in rehashing old points, particularly if they're not even relevant to the article at hand. I would recommend you look to the good behavior of Paul Dekous as an example. Paul does not believe in LIGO's results, and he reminds us of that whenever a discussion of gravitational waves comes up, along with his reasons for his skepticism. But he does not bring them up otherwise, nor does he bring up the same talking points over and over when a certain matter has already been explained to him. He is not convinced that things are a certain way, but he only brings up his pet ideas in context and when there's a new story out.
Things I have noticed here that run contrary to that come from those opposing special relativity, those furthering cold fusion, those pushing their own pet ideas about a fragile, tearable spacetime, those pushing an aether theory, and so on. Keep it relevant or take it elsewhere. These comments are for commenting on the topics discussed, not for whatever it is you have an axe to grind about. The axe-grinding is for me to decide. That's why it's a blog, not a wiki.
Image credit: Architectural rendering of the now-completed Magdalena Ridge Observatory Interferometer (MROI) delay-line facility and beam-combining laboratory, via http://spie.org/x25797.xml.
From Elle H.C. on similarities between LIGO and resonance: "The controversy around LIGO’s GWs has shown us how delicate it is to detect something shaking but not (yet) breaking, just like how difficult it is to see the glass shaking ‘significantly’ until … without the high speed camera."
Not at all, actually. What the controversy around LIGO's gravitational waves show is how difficult it is to detect a small effect at the limit of the sensitivity of your detectors, and in particular in the presence of difficult-to-quantify noise! The shaking is very easy to detect, if it's of large enough magnitude. For example, if you set up an interferometer and blow on the back side of the mirror at one end, you can simply see the effects, visually. (And yes, you can see them better slowed-down, but that's simply using a better detector than your eyes.) When you are at the limit of what you can detect, that's where you have difficulty detecting it. But if you were to improve on LIGO by making longer arms, reducing noise further, or putting it in space, the delicacy of the signal becomes far less significant. It's a question of the technology and sensitivity, not of the phenomenon of shaking.
A comet or asteroid that struck Earth because it wasn't detected quickly enough is one of humanity's greatest natural threats. Image credit: NASA / Don Davis.
From Sinisa Lazarek on saving the Earth from the warming Sun: "It will take billions of years for the sun to enter the red giant stage where this question becomes relevant. But the largest asteroids.. several kilometers large (like the dinosaur-wiping-ones) are on the frequency of several million years."
Humans are far more likely to go extinct for reasons other than asteroids, IMO, long before this occurs. When you say "several" million years, we are likely looking at frequencies that are more like ~100 million years, which is normally much higher than what we consider to be several (which I estimate as somewhere between three-and-seven). But in 100 million years, the Sun will be outputting 101% of its energy today. My point is that we have long-term problems with can start thinking about now. Just as in life, I shudder to think of people avoiding important matters because there are urgent-but-not-so-important matters to attend to. For humanity, I think it's important to remind us of those big, long-term problems every once in a while. But no exaggeration, please!
Image credit: AFP file photo, via http://www.timeslive.co.za/scitech/2014/03/10/dinosaur-killing-impact-a….
From Omega Centauri on an alternative strategy for migrating the Earth: "Can we cheat and transfer orbital energy from other solar system bodies via gravitaional interactions. One suggestion is to manipulate the orbits of asteroids, so that they repeatedly have gravitational encounters with the earth, which transfer some energy and angular momentum from the asteroid to the earth."
Sure! But if you want to do a large momentum transfer, you're going to eject the asteroid/comet/KBO in question. If you want to know how many of these objects you'd need, the answer is around 1,000,000 of them if you're talking a large-ish asteroid. So about one per thousand years over the next billion years. This is, to me, a frightening proposition. If you miss your mark by just a little bit, you'll wind up with an impact even larger than the one that wiped out the dinosaurs! Better hope the errors on your asteroid deflection system give you much less than a one-in-a-million odds of collision!
Remember, the total mass of the asteroid belt is less than the mass of the Moon; the total mass of the Kuiper belt is between 4-10% the mass of Earth. We'd need to clear out a large chunk of it to migrate the Earth, and if you wanted to significantly change the mass of another body, you'd need a better source than those places!
From the distant Universe, light has traveled for some 10.7 billion years from distant galaxy MACSJ2129-1, lensed, distorted and magnified by the foreground clusters imaged here. Image credit: NASA, ESA, and S. Toft (University of Copenhagen) Acknowledgment: NASA, ESA, M. Postman (STScI), and the CLASH team.
From skl on why even worry about galaxies and stuff: "Why do you spend so much time with your head in outer space when we’ve got a crisis down here on earth?"
Because there is more to life than worrying about every single crisis that comes up all the time. There is art, there is music, there is science, there is wonder, there is joy. Yesterday, I got up at 6 AM, wrote a letter to the newspaper, and then worked on volunteer stuff for my town from 7 AM until after 10 PM. But you know what I did at about 8 PM? I took five minutes to just look to the east, and watch the moon rise. It was full, it was yellow, and it was beautiful. Because there's more to life than focusing on "OMG all hands on deck to stop this latest catastrophe right now." Yes, it's something that is important to do. But so is being aware of what's going on in the Universe. So is the pursuit of knowledge. So is being curious. So is learning. So is trying to make existence more enjoyable and educational and informative for everyone. That's a way I can impact the world, positively, in a fashion I'm inexhaustibly passionate about.
The Earth (L) in visible light, compared with Venus (R) in infrared light. While Earth’s reflectivity will vary over time, Venus’ will remain constant. Image credit: NASA/MODIS (L), ISIS/JAXA (R), stitching by E. Siegel.
From Denier on exactly that catastrophe: "Yes Ethan! Why do you continue to ignore climate change!?? Can’t you see what happened to Venus when Trump pulled out of the Climate Accords on that planet? …And now Trump’s doing it here and you stay silent? Didn’t you hear Hawking? 250 degrees! That is not even American degrees. That is European super-hot degrees. Being that Trump only realistically has 3 1/2 years left in office that means Earth will be hot enough to melt lead on its surface in a short 40 months from now! We’re all dead! Me. You. Everyone. Dead!! By your silence I can only assume your payment from Big Oil came through."
Obviously my real terraforming goal is to turn Earth into Venus II. Then we'll all live in blimps above the clouds, while the fire people live down below. I'm attaching my tether to the politicians of the great city of Chicago. I hear they're all full of hot air.
From David on scientific history: "It’s fairly easy to find scientists from the era 1915 – 1923 who denigrated Einstein and his theories. There was an active group that fought a long hard battle to deny the Nobel prize to Einstein. They were motivated partly from anti-semitism and partly from reluctance to embrace a strange theory that many simply didn’t understand."
We have this image of Einstein as the crazy-haired old man, silly, grandfatherly, and kind, but his ideas were like scientific heresy to many. To defy and replace Newton? Absurd! To create a new physical view of the oldest known-and-understood phenomenon, one that stood unchallenged for over 200 years? How dare you! The reaction to General Relativity by many was not unlike the reaction to heliocentrism in the 1500s and 1600s. But in science, as in all things, the evidence is key. It lined up with Einstein's predictions, and still does, under all the stringent tests we've ever performed. You must listen to the evidence -- not logic, not common sense, not your own biases, not the words of a false authority -- if you want to reach the correct conclusion. That's why Einstein's theory is so powerful.
During a total eclipse, stars would appear to be in a different position than their actual locations, due to the bending of light from an intervening mass: the Sun. Image credit: E. Siegel / Beyond the Galaxy.
From rich r about confirming Einstein with a solar eclipse: "Ethan, you wouldn’t be baiting the resident anti relativity nuts with a post like this now, would you?"
I have a feeling that saying the word "Einstein" or talking about physics in general is all it takes to bait some people. But you may have heard about a little event coming to our world this August... and perhaps I'm just a little excited about it. I'll likely write about it again, soon, too.
The Twin Quasar QSO 0957+561, as gravitationally lensed by the enormous elliptical galaxy, YGKOW G1, four billion light years away. This was the first gravitational lens ever discovered, in 1979. Image credit: ESA/Hubble & NASA.
From Paul Dekous -- hey, what a coincidence -- on some commenters here: "Can you guys please stop spamming the comment section. I come here to read Ethan’s articles and comments related to those articles. There’s a line between honest criticism and slander, and you guys are moving more and more in the direction of the latter. Sure one can be rude every now and then, but when it’s day in and day out, it starts to become sickening."
Agreed. If you can't keep your irrelevant comments about your pet theories confined to the articles where they are relevant, it's off with your hea... err... commenting privileges here. Some of you will take being banned as a badge of honor. I'd rather you just knock off the bad behavior and continue to help everybody learn.
But I will give you an opportunity to defend your viewpoints: what would it take to convince you that Einstein was right about special and/or general relativity?
An artist's illustration of ideas inspired by String Theory. Image credit: Brianna T. Wedge of deviantART, via http://briannatwedge.deviantart.com/.
From Yiorgakis Pantoulis on a new 'theory of everything' I suppose: "Perhaps the mechanism that forces the known values, protects the masses, stretches the Universe’s curvature, suggests a new symmetry that suppresses CP-violation and governs these apparent coincidences and hierarchies is the high-energy field created by the mere act of observation by an Ultimate Conscious Observer. A Supreme Mind that supersedes time-space and knows very well how to keep the secrets of the Energy of His Thought."
Sure! So how can you turn that idea into a testable hypothesis? If you can do that -- complete with quantitative predictions -- you'll have an interesting theory. Remember, you have three things you must accomplish:
- Reproduce all the successes of the old, leading theory.
- Make a successful post-diction of at least one observation that cannot be successfully explained by the old theory.
- Make a new prediction that we can then test against the old-and-new theories, to discern between the two.
Do that, and you've got an interesting scientific theory. Fail to do that, and at best you're engaging in pure mathematical, philosophical, or theological speculation.
U.S President Donald Trump signs an Executive Order to reestablish the National Space Council as Buzz Aldrin looks on. Image credit: Olivier Douliery-Pool/Getty Images.
From CFT, on me daring to write about Donald Trump and his use of infinity: "So….you really have nothing to say this time? Maybe you should keep your mouth shut then…until you actually have a topic of conversation besides ‘Trump isn’t using the word infinity correctly.’ Sheesh Ethan. Get a life, or at least a clue."
Hmm... so that's your takeaway? Because here's mine, from the article I wrote:
The most frustrating thing about the President's statement is that he's very clearly talking about something that he hasn't bothered to learn the basics of, yet wants to sound intelligent and authoritative when it comes to it. "It could be infinity" is code for, "I don't need to know any more than I currently do, and neither does anyone else." Maybe that's true, but there are people who study this for a living. If you're curious about it, you can get that information in any number of places... but you won't find an awareness or an appreciation for it in the nation's highest office.
As dean noted: "People wonder why the current president is viewed as a massive embarrassment: his meaningless jumble of words in that “speech” should be one of the primary points of evidence." I think it's worse than that, though. It's the fact that what he says has no bearing on what the actual, known information is. It's like that part of it is irrelevant. I used his statement to share the actual knowledge, and to raise awareness of the importance of actual knowledge. You may disagree that such a thing is important, but you are not going to convince me that ignorant ramblings that end in "you can't prove me wrong" are equal in validity or their inherent interesting-ness to actual, robust, scientific knowledge.
And finally, from Naked Bunny with a Whip on falling into a black hole with a tether to the outside: "Why wouldn’t it [the tether] snap? The atoms of the rope are held together by electromagnetic forces. If the atoms that are inside the event horizon can’t emit any virtual photons outward anymore, then what keeps the rope connected enough to slurp it in?"
Imagine you're in free-fall, and you're on a trajectory so that part of your ship will go inside the black hole while other parts remain outside. Now, you're in free-fall in a gravitational field, so Einstein's equivalence principle holds. You can't tell the difference between gravitation and uniform acceleration. Are you telling me that your ship must be torn apart by the event horizon's existence, even if the tidal forces are tiny at the event horizon? It's also possible that an additional force can draw the outside part in; remember a lack-of-force in one direction is the same, effectively, as an extra force in the opposite direction. What's not possible is that you can pull something that falls in back out.
Thanks for keeping it real, everybody, and I'll see you back here tomorrow for more science, more stories, and more wonders of the Universe here on Starts With A Bang!
Ethan Siegel wrote: "But I will give you an opportunity to defend your viewpoints: what would it take to convince you that Einstein was right about special and/or general relativity?"
Start a discussion about the most relevant experiments - Michelson-Morley and Pound-Rebka - and try to show that they confirm Einstein's relativity (as brothers Einsteinians universally teach). I will show that these two experiments unequivocally DISPROVE Einstein's relativity.
Are you telling me that your ship must be torn apart by the event horizon’s existence
No, I was asking why that isn't the case. Apparently, it comes back to the idea that an object falling into a black hole sees one thing while an outside observer sees another because of their differing reference frames. I never could understand that, as hard as Leonard Susskind tried to explain it in The Black Hole War.
@Pentcho Valev - since the Michelson Morley experiment was well known to Einstein and his theory of special relativity fully explained their results, I'm not sure how you intend to prove that it disproves Einstein. Pound-Rebka was designed to test Einstein's theory of general relativity, and it is generally accepted that it dd to quite reasonable precision.
Are you telling me that your ship must be torn apart by the event horizon’s existence, even if the tidal forces are tiny at the event horizon?
The tether is composed of atoms connected to each other through bonding. That bonding requires the electromagnetic force to function. It can't function between an atom inside the event horizon and one outside the event horizon, even if they are separated by a mere angstrom (approximately the length of a C-C single bond), because that functioning requires a virtual photon to travel between the inside-EH C atom and the outside-EH one...which you've stated, Ethan, can't happen.
However you are probably right in implying/inferring that there isn't going to be some binary change at the EH. My guess is bonding properties and lots of other things start to change as you approach the EH. And there's going to be time dilation involved. So from "the tether's perspective" maybe it sees a slow spaghettification or maybe the breakage takes an infinite amount of time...but from a distance observers perspective, yes I think it happens right at the EH.
@eric and bunny
I think the confusion comes from when will that tether break.
In the scenario where one ship is outside of EH and has enough fuel, and other is inside the EH and has enough fuel, and they are connected by the tether. As long as both ships can sustain their possition.. the tether won't break. But this situation can't last forever of course. If the ship within the EH can't sustain it's position and starts to be drawn even closer to the inner regions of BH... and the ship outside maintains it's position outside the EH.. then yes.. eventually the tether will have to break.
But it might be possible (some calculation needed beyond my skill), for a ship within the EH to achieve a relatively stable orbit within the EH yet not to be drawn into singularity for months/years... of course, this would require a very large black hole with a relatively shallow gradient beyond EH.. and some powerful engines... but is a valid scenario... as long is it can correct for the pull by it's engines. It can't send any signals outside of course... but can sustain itself within EH and not be directly drawn to the center.
Just crossing the EH with tether connected, won't cause the tether to break instantly.
I don't get your objection, because we can all see the glass but not the small vibrations, therefore we need a better high speed camera. The same goes for LIGO we can see all kinds of vibrations even with a basic seismograph, but to see GW we need a better detector. As you write:
"It’s a question of the technology and sensitivity"
And the other problem with the LHC is the same as with LIGO, there's too much noise to clearly see small 'side effects' such as GWs or tiny vibrations caused by particle collisions.
At LIGO we can eventually reduce and escape as much noise as possible by setting LISA up in space, but for the LHC there's no escape.
Ethan Siegel wrote: "But in science, as in all things, the evidence is key. It lined up with Einstein’s predictions, and still does, under all the stringent tests we’ve ever performed. You must listen to the evidence — not logic, not common sense, not your own biases, not the words of a false authority — if you want to reach the correct conclusion. That’s why Einstein’s theory is so powerful."
This is wrong. Logic comes first - a physics theory should be DEDUCTIVE (general relativity is not). If the theory is not deductive, it is an empirical model that can be endlessly adjusted, and looking for supportive evidence makes no sense. Sabine Hossenfelder is starting to understand this:
Sabine Hossenfelder: "Many of my colleagues believe this forest of theories will eventually be chopped down by data. But in the foundations of physics it has become extremely rare for any model to be ruled out. The accepted practice is instead to adjust the model so that it continues to agree with the lack of empirical support."
Sabine Hossenfelder: "The criticism you raise that there are lots of speculative models that have no known relevance for the description of nature has very little to do with string theory but is a general disease of the research area. Lots of theorists produce lots of models that have no chance of ever being tested or ruled out because that's how they earn a living. The smaller the probability of the model being ruled out in their lifetime, the better. It's basic economics. Survival of the 'fittest' resulting in the natural selection of invincible models that can forever be amended."
Pentcho - I trust you have scrubbed your life of all the goods, processes and services that depend of relativity (either special or general) for their existence in modern times? I trust you have maintained your integrity on that? That you aren't simultaneously preaching against it's validity while benefiting from all the modern benefits that depend on it being a real phenomenon?
Wait, you're using a semiconductor device to post your sermons, aren't you...
not that this will matter to you, of course, since you've proven time and again that you are not willing to learn but just copy/paste ad hoc.. but non the less..
just because YOU don't know something.. or can't deduce something, doesn't mean it's not done or can't be done.
p.s. your statement that GR is not deductive is simply false. As well as your follow up that it's an empirical model that can be adjusted endlessly.
GR came deductively from hypothesis which formed a theory... and no empirical evidence existed for it when it was created. It was tested and proved correct... it's sort of a dictionary example of what a deductive method is.
Sinisa Lazarek wrote: "GR came deductively from hypothesis which formed a theory… and no empirical evidence existed for it when it was created. It was tested and proved correct… it’s sort of a dictionary example of what a deductive method is."
- maxwell's equations
- lorentz transformations
- equivalance principle
Sir, you yourself play pretty fast and loose with the whole 'infinite' concept yourself. Truth is, you really don't know if the universe is bounded, or open, infinite or not, depending on what 'exponentially spatially expanding' kick or flavor of the month theory of the multiverse you think you might be living in, for grief sake, you actually show absurd 'artists depictions' of crap like superstrings (you can't even be remotely serious if you show images of nonsense like this) or 'pocket universes' and 'bubble universes' detaching and rising like bubbles in carbonated soda (pray tell what vantage point are you at to even observe such a thing???) , which are based on ZERO measurements and ZERO observations. Uninformed mathematical fantasy is still just fantasy.
Trump actually said nothing wrong. You are just being a nitpicking ass who is looking for something to nag about.
For some perspective on the ignorance of presidents,
you could easily parse the words of every president that has ever served and find far worse factual 'faux pas', such as the 'most intelligent president EVER', the previous president commenting on having visited all "57 states", or discussing the 'Marine CORPSE' with servicemen (he did this several times, even after being corrected and told how offensive and ignorant it was) , and admitting he didn't know how to say something in 'Austrian'.
"Trump actually said nothing wrong."
That last word isn't needed. He said nothing. There was no context to his ignorant babbling. That is the point.
Sinisa Lazarek wrote:
"– maxwell’s equations
– lorentz transformations
– equivalance principle"
These are the hypotheses from which Einstein deduced general relativity?!? You are not the cleverest Einsteinian, Sinisa.
And by the way cft, you can stop the "Marine Corpse" lie. It never happened. He talked about Naval hospital corpsman, and included the p and s. The only bit marginally true is that he used the "p" while neither of the two primary pronunciation does (one allows for an "s" or a "z" sound, the other allows those sounds to not be made).
It's also worth noting that President Obama, the same day, referenced his error on the 57 states bit.
The difference between the things you point out and the "comments" President Trump made is simple: some are pronunciation errors and errors in speech that the person admitted to, and the other was intended to be a series of serious comments but which were, in fact, completely empty of any meaning or relevance to the occasion. I realize that they are impossible to defend directly, but your attempted redirection is pathetic.
"I will show that these two experiments unequivocally DISPROVE Einstein’s relativity." Write it up for Ethan and please just just show us.
By the way Ethan, I love the your articles and writing. As an engineer i have just enough science background to be dangerous and your topics keep my interest and keep my brain bubbling!
"just show us"
If Ethan starts a relevant discussion (e.g. "Experimental confirmations of Einstein's relativity"), we could analyse many crucial tests - Michelson-Morley, Pound-Rebka, Muon lifetime, Alväger experiment, de Sitter-Brecher double star, Mercury precession, Eddington-Adams 1925 measurement of Einstein's redshift, the recent measurement of the mass of the white dwarf, etc. Any of them is either fraudulent or inconclusive.
"These are the hypotheses from which Einstein deduced general relativity?!?"
yes pentcho... when you combine maxwell's theory of EM propagation with realization that lorentz arrived, you logically arrive at special relativity. Wen you then add equivalence principle to that.. you arrive at GR. And as far as Einstein, most of it was deductive reasoning with thought experiments..
For someone arguing against all that, you sure lack in the basic fundamentals of it. And when you, who doesn't even realize the blue/red shift of light (which can be tested by anyone with couple of hundred dollars of gear), ...say "you're not the cleverest"... well.. I can only take that as a compliment dude, since your ignorance and arrogance is mind blowing at this stage.
As long as both ships can sustain their position.. the tether won’t break.
Ethan has implied in other posts that this can't happen: that once inside an EH, all matter must immediately proceed to the singularity because it's impossible for any force-carrying particle to move outward. My point about tethers is really just an addendum to that; Ethan is right, but what he states for "unattached" objects also applied to "attached" ones, for exactly the same reasons - the force-carriying particles responsible for bonding can't move between any subatomic particle "further in" and one further out. Thus 'forming a bond' is in the same predicament as 'moving outward.'
I'll try to dig some more for either proof or refutation, but just a quick reply...
a while ago I found this paper..
and while the topic itself is speculative and irrelevant (that of life)... the finding that there ought to be some orbits which are at least semi-stable, I found fascinating. I didn't look further and don't know if this was refuted or not, nor can I claim the calculations are correct or not.
But that;s why I think that if you get within the EH and have some means to resist the pull (engine), while you will never be able to go outside, you might at least (for a time) try to resist the pull and not imediately plunge to the singularity.
p.s. the above seems to work with kerr-newman metric or with reissner-nordstrom metric .. both dealing with charged BHs.. Yet we don't think those exist...
Ethan: 'But I will give you an opportunity to defend your viewpoints: what would it take to convince you that Einstein was right about special and/or general relativity?"
Regarding length contraction, It would take a clear disambiguation of the difference between *apparent* contraction (as seen/measured by various observers) and *actual physical shrinkage* as claimed in the pole- in- a- barn and the train- in- a- tunnel SR thought experiments... also applied to flattened planets (as seen by...) and contracted distances between stars, as per fast travelers with slow clocks.
Everybody but SR believers knows that there is no physics of shrinking objects or astronomical distances as per SR.
Regarding time dilation, it would take a serious ontology of what time IS, and then it must quit ignoring and begin considering the history of each clock which keeps time differently after exposure to different forces of acceleration to reach different velocities or exposure to differences in gravity fields. Finally a recognition that for all of us living on Earth, the precisely standardized revolution and orbit define standard time for a day and a year and all fractions thereof. (Other planets will have their own standard day and year.)
Then no one will be deluded into believing that the distance between stars contracts as a hypothetical traveler's clock ticks more slowly.
Finally regarding GR, many critics, myself included, acknowledge that the geometric model for the math is an improvement in trajectory predictability over Newtonian physics. But the criticism remains that "spacetime" is promoted as an actual entity, a malleable medium in the real world with no ontology of what it IS or explanation of the mechanics of what gets curved my mass or how mass is "guided" by this curvature. The whole "thing" was conceived as a way to explain gravity without a "force of gravity" acting at a distance, which Einstein would not accept. The map is still not the territory. I expect that developments in understanding the Higgs Field will eventually explain gravity better... as all space being filled with energy quanta... no more "spooky action at a distance.
Thank you for the opportunity to "defend our viewpoints."
Sinisa Lazarek wrote: "when you combine maxwell’s theory of EM propagation with realization that lorentz arrived, you logically arrive at special relativity"
Einstein deduced special relativity from the principle of relativity and the assumption that the speed of light is independent of the speed of the light source. He didn't deduce anything from "maxwell’s theory of EM propagation" and "realization that lorentz arrived". You simply don't know what you are talking about. A totally confused mind.
@Sinisa Lazarek #21:
My understanding is that you don't have to plunge directly into the center of the black hole -- you can orbit it inside the event horizon, albeit not stably -- but you will move steadily toward it because your local light cone has tilted so much that any motion sends you closer to the singularity. In other words, the singularity is inevitably in your future.
But that still doesn't explain why the tether doesn't snap at the event horizon as virtual particles are no longer able to propagate from the atoms inside the horizon to atoms outside the horizon. As I stated earlier, it sounds like my problem (and Eric's) is that we're only looking at this from the reference frame of someone staying outside the horizon, and not from the reference frame of the rope itself, but I don't get how that works.
“From skl on why even worry about galaxies and stuff: “Why do you spend so much time with your head in outer space when we’ve got a crisis down here on earth?”
Because there is more to life than worrying about every single crisis that comes up all the time. There is art, there is music, there is science, there is wonder, there is joy.”
Except there won’t be any art, music, science, wonder, or joy when, as Richard Hawking said, the earth is frying at 250 degrees.
@ Naked Bunny #25
I hope this will help. Of all the lectures on GR, I found these ones to be the easiest to follow. (Guth's open course is also great but more for general understanding of metrics and geometry. Susskind's are too math heavy for me).
Of course, the ideal case would be to watch all of them.. but that will take some time... But this one should IMO shed light on the topic about event horizon. Yes, it's an hour and half, but it is time well spent :) Again, hope this clarifies some issues, much better than I could write here in couple of sentences.
p.s. first 15 minutes might be a "turn off" .. but at about 15' onward it gets to the interesting part :)
just to sum.. if you still decide to not watch the whole lecture...
1. schwartzschild solution (what you & eric are thinking about) applies ONLY to an observer very very far away from the black hole
2. schwartzschild solution has 2 singularities. One at R=0 (the center of black hole), and R=Rs.. the event horizon
3. for i.e. a ship very near the black hole or near what a far away observer would call event horizon, the schwartzschild solution is NOT the correct solution.
4. the solution to field equation for an object near a black hole or inside the black hole DOESN'T have a singularity at R=Rs. It does have one for R=0.
So if we disregard the tidal forces... there is no reason for the tether to break for the reasons you might think that come from schwartzschild solution, since there is no singularity for them at the event horizon.
Thank you for the links and the summary, Sinisa. I appreciate your expansion on Ethan's original response. It looks like I need to block out some time this weekend and put on my concentration glasses.
To Sinisa Lazarek
Something that's come up in the comments before, and may or may not be related to this:
is that there is a minimum radius for a stable orbit for any black hole, and it's further out than the event horizon.
As for Ethan's post, I'm not seeing why he said the tether wouldn't snap and would probably pull you in either.
It looks like he started out by saying matter couldn't even hold itself together inside the event horizon because the force mediating particles would all hare off to the singularity instead of holding their existing structures together, so, assuming the hypothetical ship holding itself in place and dropping that tether, I don't see why you couldn't just pull and get a shortened tether back.
I realize all of this is working with analogies, the force mediating particles are virtual, and so on, but it did seem like that was the direction Ethan's conclusions were headed before abruptly switching gears in the second to last paragraph of the article.
This is interesting to me, because most descriptions of 'spaghettification' are very cartoony, and I found it fascinating when Ethan first mentioned the whole 'matter falling apart inside the event horizon as every particle takes it's own individual orbit to the singularity', backed up by when he's said that no particles could move away from the singularity either, and so on.
If you look up this stuff elsewhere, you'll see all sorts of official sounding arguments that you can cross the event horizon of a massive enough black hole unscathed, only being spaghettified once you're much deeper inside, so I'd love to see Ethan's more authoritative take on this.
So, based on this and other of Ethan's posts, I'm now envisioning spaghettification as something that happens outside a black hole's event horizon, and inside would just be disintegration.
So, which is it? I'd love to have a better understanding of this!
Thanks for your time!
lot's of questions :)) Ok, first a disclaimer... I'm not a physicist, let alone a professor of astrophysics. So I don't really dare go into the finer points between different metrics and conversions between different coordinate systems and especially into analysis of differential equations (which inevitably you have to do in order to get a precise answer to what happens where and how).
But I do consider myself an intellectual with a huge addiction to astrophysics. So the best I can do is point to relevant documents/media that I used to educate myself. With that said, I will try to give my understanding to your questions, but I would advise that you try and read/watch as much as you can from actual astrophysicists about this subjecy and maybe you arrive at different conclusions, and then share them. That way we can all grow in our knowledge/understanding.
So here's the thing... (some of it just re-hash of what I wrote to Bunny). When we talk about BHs in general... it's almost always the Schwarzschild solution to Einstein field equations. And then.. it's usually a very wattered-down version of those solutions, with things important to this conversation left out. One of those things is that the picture we paint is for an observer which is strictly speaking infinitely far away from BH. He never sees anything actually crossing the event horizon, because at the event horizon, in schwartz. solution time actually stops, and light coming from it is infinitely red shifted. In other words, schwartz. solution has a singularity at the event horizon (but this one is coordinate dependent, as it doesn't show in other solutions, and thus we don't think of event horizon as some "force-field".. not counting QM/firewalls etc..just sticking to pure GR).
In order to get a sense what it would be like to enter a BH and cross the EH, we can't use schwarzschild solution and metric anymore, we have to use a different set of coordinates. Those that don't describe a static observer far away, but instead someone going into a black hole. Thus Gullstrand-Painleve coordinates or alternatively Kruskal-Szekeres coordinates and field equations. When you solve them.. you don't get anything problematic at the event horizon. Yes, space is extremely curved in comparison to flat space-time, and all geodesics beyond EH point to the singularity at the center, but there is no singularity at event horizon. Time doesn't infinitely slow down for you crossing it. And if the BH is super massive and event horizon large, and gravitational gradient between nearby slices of space-time shallow enough... you don't get disintegrated just by crossing it. As you approach the singularity at the center and curvature gets more extreme... yes, eventually you will break up.. but not at event horizon or just inside it.. but much further deep down.
So this bring us to spaghetti. This doesn't have anything to do with a particular set of coordinates, but instead has to do with that grav. gradient between consecutive slices of space. If it's a small black hole (several solar masses).. the gradient is very steep... and you would get stretched well before you ever reach the horizon as the difference in force (or more precisely curvature) between your feet and head would be more than your muscles/bones can withstand. But if it's a super massive black hole... then that gradient is relatively shallow and you wouldn't experience that. The gradient would become severe only close to the R=0.
And lastly about the tether... So basically... for the ship outside of black hole.. but not on the radial path towards it... (let's say they have engines that can push to 0.99999c)... as we saw above in schawtz. solution... they would not actually see anything crossing the horizon... they would see the other ship slowing down.. redshifting to blackness... then starting to get pulled in as well.... the tether would break because of opposing forces acting on it (ship outside going in opposite direction of the one now inside)... but if they don't start reversing... the tether won't break... instead they would start going in and crossing the horizon as well.
So yes.. it is strange... but that's why it's cool :)
Sinisa @33: I agree with what you wrote to Adam in #168 but I think his point is that a ship outside the EH can't maintain a slowly degrading orbit around the BH *and* have the tether not break. During the time the orbit is degrading but the ship is still outside the EH, the bit of the tether inside the EH can't send force-carrying particles "up" the tether to the bits outside the EH. Thus the atoms can't remain bonded.
But as you say, what a distant observer see will be very different from what an astronaut hitched to that tether will see. Without Newtonian simultaneity, it's entirely possible that the distant observer experiences the tether 'freeze' at the event horizon while the ship experiences something else and the tether inside the EH experiences some third sequence. Does it suddenly break or slowly stretch? Perhaps both, depending on who you ask.