Physicists confirm two cases of “elusive” black hole/neutron star mergers
arstechnica.com
arstechnica.com
1. What if you were 1 light year from such an event? What would you experience? What about 100 light years?
2. What does warping spacetime really mean? I know this happens around a black hole. But what would the macro effects of this be?
3. So the universe is expanding. Does that mean more "space" is being made? If so, how? Out of what?
(Or are you saying that the gamma rays are emitted earlier in the merger process than the gravitational waves?)
https://physics.stackexchange.com/questions/560833/could-a-h...
According to a 1948 paper by Bekesy [0], a human ear can detect sounds through several mechanisms. In a gravitational wave, since the whole head would vibrate, sound would reach the ear by bone conduction through the skull. Fortunately, this also happens to be the most sensitive mechanism. The smallest vibration amplitude detectable by bone conduction is about 4 x 10^-9 cm at around 3 kHz. If a typical skull is about 17.5 cm from front to back, that gives a minimum detectable wave amplitude h (the fractional expansion and contraction of spacetime) of about 2 x 10^-10.
The frequency of the gravitational waves produced in a collision between a neutron star and a small black hole turns out to be pretty close to an optimal match for the human ear. To estimate the amplitude, the first black hole collision detected at LIGO produced a strain of about 10^-21 at a distance of 410 Mpc. (The events in the article were smaller, but within the same order of magnitude.) Thus, since the amplitude scales as 1/r, the gravitational waves from the collision in the article would have been theoretically audible at a distance of about 400 AU or 40 billion miles.
Alas, attempting to test this calculation experimentally would incur certain practical difficulties. Notably, you would be vaporized by gamma radiation from the collision several seconds before the gravitational waves became audible.
What got removed from my original was effectively “could a human even hear this in principle?”, with my thoughts at the time being “or would you require an gravitational wave intensity so great that the energy of the gravitational waves would be enough to spontaneously collapse into a black hole?”
400 AU from a (stellar mass) black hole-neutron star merger isn’t going to be that intense, and is therefore implicitly gives me my answer (even if the environment itself would be deadly for other reasons).
How much lead shielding would you need to survive such a thing? Would standing on the far side of an Earthlike planet absorb the gamma rays?
My guess is that you'd still die from shock waves propagating through either the atmosphere or the planet itself, but it's difficult to predict the exact effects.
Maybe you could provide a more detailed answer THERE instead?
1. always wondered the same. i'd suspect that for most astronomical BH you would first need to worry of X/gamma rays. you could possibly hear a loud chirp since it is audio frequency.
2. the warping of space time here on earth is actually mostly a warping of time, which is even weirder. i means that the time at your feet is flowing slower that where you're head is. about one second on your entire life. that's actually WHY you feel earth gravity.
3. yes, more space is created out of nothing! because there's a vacuum energy density that inflate the local patch of universe.
funnily why all of the above is hard to understand for our human brains, it all makes sense in the mathematics..
i highly recommend the YT channel PBS Space Time for more explanations
I don't think you can say that with that kind of certainty. We don't have a theory of quantum gravity, we don't know what dark matter is, and we don't know what 'dark energy' is, so we don't actually know what is driving the expansion of the universe, so saying that 'space is created out of nothing' is too strong. Even something like the theory of cosmological inflation, which has some explanatory power, hasn't been experimentally verified, but rather tuned to match the observations.
It's something I've noticed in a lot of communicators of science (whether they have a background in science or not). They tend use terms that overstate our actual knowledge in some specific area of science.
well, any classic (in SM sense) QFT will produce positive vacuum energy density which translates into negative pressure. P = -E
i'm almost certain (no proof tho) that space time itself is just an illusion (and that there is only "information ").
in other term i know i know nothing (but still is able to give predictions up 10^-32 s after big bang)
Of the four fundamental forces, the higher order aspects of gravity effect humans the least. Satellite operators may need to correct their clocks every once in a while, but other than that, we just can't reach the speeds or distance from earth to notice time dilation, nor can we collide masses large enough to detect gravitational waves.
I was shocked in college when my General Relativity professor told me that very few scientists are studying GR, most likely because it's surprisingly more intuitive than quantum physics, and it's harder to experiment. I really wanted gravity to just be... cooler, I guess.
Perhaps quantum loop gravity will interest you.
it's a quite active area of research even tho it's more than a 100 yo, check gr-qc on arxiv
https://www.amazon.com/Black-Holes-Time-Warps-Commonwealth/d...
Most of their videos are in the 8-13 minute length, and they do a pretty good job at the start of each linking back to earlier episodes that cover prior material that the current video builds on, so if you see a video whose title/topic seems interesting it is fine to start their first.
[1] https://www.youtube.com/channel/UC7_gcs09iThXybpVgjHZ_7g
5 solar masses is 1x10^34 g. 1 g of mass is roughly 0.9x10^14 J (mc^2).
So, roughly 1x10^48 J.
1 ly is roughly 1x10^16 m. Surface area of a sphere with r=1 ly, is 4πr^2 = 4π x 10^32 m^2 or roughly 1x10^33, so each m^2 of surface will receive 1x10^48/1x10^33 = 10^15 Watt, or about 10^12 x brighter than our Sun on Earth in sunny day, but for 1 second only.
2. Spacetime is 4d array: [x,y,z;t]. Warping of spacetime means that a scientist applies a mathematical formula to the array directly, like shader in OpenGL. It has no physical meaning. It just a quick way to simulate unknown physical process, to make a prediction.
3. No, it doesn't. Our local group of galaxies is expanding, but this is a coincidence. Actually, we are falling into a black hole. Nearest big black hole is in the center of our galaxy, then Great Attractor, then Shapley Attractor.
Sounds hot. Flash burn everything not made of stone. Land life wouldn't survive?
If you release 5 solar masses of energy in one second, electromagnetically and with the same spectrum as the sun, half way between the Milky Way and Andromeda, every star in both galaxies would see it only a little dimmer as Sol appears on Mars.
https://www.wolframalpha.com/input/?i=%28%28%285+solar+mass%...
It seems like the universe would be immeasurably more dangerous than it already is, if all of these events were primarily EM radiative in nature.
As a non-physicist, I'm also curious how gravity is simultaneously so much weaker than the other forces, but yet spacetime seems to be able to stably survive these immense releases of energy.
2. I suppose it's still possible to illustrate. We can imagine that the spacetime gets "bulged" a bit, so light rays become slightly bent when passing it. It's likely impossible to notice with a naked eye from inside without being torn by tidal forces. But it's quite visible from some distance: pictures of gravitational lensing on astronomical scale are easy to find.
All these merging events that we are picking up now - are there still on-going events or has the frequency dropped off as the cosmos have moved apart and relative, to early years, "settled" down?
If you are asking if gravitational waves move at the speed of light, then yes, they do.
If that happened 1.2 B years ago and the cosmos started approx 12 B ago. Are there events happening still or have they dropped in frequency?
(I don't know that I could recommend Diaspora. It's dense and I think requires a level of familiarity with quantum physics to truly enjoy. It felt like a bit of a slog for me...)
Here’s a video, he talks about the redshift around the 8 minute mark. https://youtu.be/vNaEBbFbvcY
But the universe does loop back on itself, presumably. All matter and energy will eventually slow down and reverse course and be drawn back to the center.