stupid physics questions

[zip accident]

Yet about that famous/infarmous Hawking Radiation I really would like once to someway find an explanation that I can
understand that would satisfy me enough to think "ok, I can see now WHY they thing this is SUPPOSED to happen".

Wikipedia

A slightly more precise, but still much simplified, view of the process is that vacuum fluctuations cause a particle-antiparticle pair to appear close to the event horizon of a black hole. One of the pair falls into the black hole whilst the other escapes. In order to preserve total energy, the particle that fell into the black hole must have had a negative energy (with respect to an observer far away from the black hole). By this process, the black hole loses mass, and, to an outside observer, it would appear that the black hole has just emitted a particle. In another model, the process is a quantum tunneling effect, whereby particle-antiparticle pairs will form from the vacuum, and one will tunnel outside the event horizon.

I personally find the idea of Hawking Radiation far more intuitively appealling than the idea of a singularity with immense mass but no width.

[pogo]

It's still a THEORY NOT PROVEN by any experiment/measurement so far, so as far as I know "We do not know", it could
well be that micro black holes would not evaporate at all .. and that would be "fun" then .. if they ever will manage to make one ..

One argument for it is that micro black holes can be made in the lab, or at least in the particle accelerator. The could be made in stars, maybe in stellar explosions. Certainly we believe (with lots of evidence) that the universe was once much smaller, much denser, and so much more suited for making black holes. If they do not evaporate where are they ? They should be easily detectable as they will distort spacetime wherever they go. Arguably they should eat up all matter as they are made and come into contact with stars and planets. But we're still here and we can't see any micro black holes, which suggests Hawking is right: black holes that don't evaporate are massive, require a lot of mass to form, and so thankfully relatively rare compared to stars and planets.

[zip accident]

Thinking about gravity waves, when two wave trains cross, and you get interference, are the nodes black holes, and if so do they disappear again when the wave trains stop crossing, if so, why?

[pogo]

I think gravitation waves will dissipate from a source inverse-squarely, so will be everywhere much less intense than the source, so even if two waves intersect they will not be strong enough to produce any such effect. If you could maybe focus the waves, using some sort of lens, like light can be focussed by a magnifying glass, but I don't know what form such a lens would take.

[zip accident]

I think gravitation waves will dissipate from a source inverse-squarely, so will be everywhere much less intense than the source, so even if two waves intersect they will not be strong enough to produce any such effect. If you could maybe focus the waves, using some sort of lens, like light can be focussed by a magnifying glass, but I don't know what form such a lens would take.

Yeah, the 1/x^2 rule applies, but if you have this situation then presumably they are producing gravity waves at the time of emission of the light we are currently seeing, and thus, at that time (in the billions of years since then they've presumably merged, so there's probably not much happening now), why wouldn't new black holes be spawning at the nodes of the gravity waves given off?

I'll add that I'm sceptical of gravity waves, possibly for no very good reason, I certainly want to see this explained before I think any further about abandoning that scepticism.

[pogo]

For gravitational waves I think you need a moving gravitational source, which would rule out a supermassive black hole as it doesn't move: it would need something nearby which it was being draw towards or which it was orbiting, clearly with comparable or greater mass, but such black holes tend to be one per galaxy. Basically your sources are likely to be much less intense: more precisely the bigger the source the slower it will accelerate, limiting on the intensity of waves. I suspect also these waves are pretty weak, even for large masses, as otherwise two interacting bodies, orbiting each other say, would lose energy, something we don't see happen even on astronomical time scales: the Earth has been orbiting the sun for billions of years. It would also explain why we have such a hard time confirming they exist, they are just too weak.

[zip accident]

For gravitational waves I think you need a moving gravitational source, which would rule out a supermassive black hole as it doesn't move: it would need something nearby which it was being draw towards or which it was orbiting, clearly with comparable or greater mass, but such black holes tend to be one per galaxy. Basically your sources are likely to be much less intense: more precisely the bigger the source the slower it will accelerate, limiting on the intensity of waves. I suspect also these waves are pretty weak, even for large masses, as otherwise two interacting bodies, orbiting each other say, would lose energy, something we don't see happen even on astronomical time scales: the Earth has been orbiting the sun for billions of years. It would also explain why we have such a hard time confirming they exist, they are just too weak.

That's why I linked to that quasar, it has two, the smaller 100 million solar masses (25x as massive as Sagittarius A*), the larger the largest known at 18 billion solar masses. At an orbital duration of 11 to 12 earth years, they were close enough to make any sort of gravity waves that are ever going to be made.

[Darkflame]

I'm not quite understanding the principle of how two gravational waves would produce a black hole at their nodes regardless of how strong they are, surely while the combined magnitude of the gravity might end up being enough to cause a black hole (if there is mass in that space), the direction would be wrong? Its not going to pull it "inwards" like the mass's own gravity, it would be being pulled towards one or both of the sources

Or is it that, under this model, gravity never has a direction, only an amplitude, and things tend towards whatever is the highest level of gravitational intensity in the surroundings? In which case I guess two things that are nearly black holes could cause an actual black hole where the ripples overlap, provided there is mass their to collapse. (else its just potentially/temporarily a black hole).

[zip accident]

I'm not quite understanding the principle of how two gravational waves would produce a black hole at their nodes regardless of how strong they are, surely while the combined magnitude of the gravity might end up being enough to cause a black hole (if there is mass in that space), the direction would be wrong? Its not going to pull it "inwards" like the mass's own gravity, it would be being pulled towards one or both of the sources

Or is it that, under this model, gravity never has a direction, only an amplitude, and things tend towards whatever is the highest level of gravitational intensity in the surroundings? In which case I guess two things that are nearly black holes could cause an actual black hole where the ripples overlap, provided there is mass their to collapse. (else its just potentially/temporarily a black hole).

I don't quite know, that's why I thought this thread was perfect for it.

However, gravity waves are not normal gravity to start with, they are waves in the normal gravity, and when nodes arise in waves they tend to be relatively static, but strong. I therefore don't know what nodes in gravity waves would mean, but if they did mean temporary black holes that turned out to be permanent, then that would mean we were getting matter from nowhere, and that seems wrong to me, which is one reason I don't think there are gravity waves.

I accept that we may have theoretical reasons to want them, and effects that look like the expected results of having them, but think there is probably another, as yet unknown mechanism that does that. As I understand it, we've been building gravity wave detectors that we expected to be good enough since at least the early 1970s (I remember having conversations about them at that time), and we haven't detected waves yet. We've been aiming for fusion power since the 1970s too, but in that case we knew darn well we were a long way off, I think it was in the 1980s that it was said that fusion in toruses was going to take another 50 years work.

[disciple]

Hi,

Can I ask another stupid physics question please.

Travel near the speed of light, for sake of argument "at". If a star was 100 light years away then is it correct to say that it would take you 100 years of time (from the perspective of the traveller) to reach it?

[gravy]

Hi,

Can I ask another stupid physics question please.

Travel near the speed of light, for sake of argument "at". If a star was 100 light years away then is it correct to say that it would take you 100 years of time (from the perspective of the traveller) to reach it?

No

As well as time slowing down the distance you need to travel contracts the faster you're going.

Just because of time dilation if you didn't need to accelerate / decelerate for the journey and you could travel at the speed of light for the whole journey the journey time would be zero.

[gilesgoat]

It's still a THEORY NOT PROVEN by any experiment/measurement so far, so as far as I know "We do not know", it could
well be that micro black holes would not evaporate at all .. and that would be "fun" then .. if they ever will manage to make one ..

One argument for it is that micro black holes can be made in the lab, or at least in the particle accelerator. The could be made in stars, maybe in stellar explosions. Certainly we believe (with lots of evidence) that the universe was once much smaller, much denser, and so much more suited for making black holes. If they do not evaporate where are they ? They should be easily detectable as they will distort spacetime wherever they go. Arguably they should eat up all matter as they are made and come into contact with stars and planets. But we're still here and we can't see any micro black holes, which suggests Hawking is right: black holes that don't evaporate are massive, require a lot of mass to form, and so thankfully relatively rare compared to stars and planets.

One argument my arse, is there any so far evidence they EVER created one of such micro black holes anywhere ?

I don't think there is and/or they never managed to make one so far otherwise it would be all over the news.

Anyway further study tells the even a black hole has an horizon, if you don't happen to be in the proximity of it you won't be sucked in or such, yes it would have the gravitational field of mass X but that's about it, it does not mean that "all the universe is going to fall in that".

Certainly things would be completely different if everything would be static ( no momentum, no moving ).

However we are on Earth, yes Earth has a gravitational field, yes is not strong enough to squeeze it into bits yet we can't just jump and escape orbit, however with proper speed is possible.

Black holes do exist and there are quite a few that are certain to be and even more candidates quite certain to be, also some new theories say "every galaxy has a supermassive black hole at its center" and our galaxy is no exception, they seems to be not "so rare" as one would think.

Where are they ? There are quite some it seems, luckily quite far away but a few ones are quite observable it seems
( well you can see their interaction with what's around them ).

I can't remember where I read it there is some ( nutter ? ) that claims that "at the singularity of a black hole a new big bang is formed and black holes are a kind of 'natural way' the universe replicates itself" .. someone claims "the purpose" of the black holes in nature is a kind of self-replication .. but this is "just another of those theories".

However I think I read also that this theory seems to be less nutters than what it looks.

I don't believe Hawkings is right ( or anyone else ) until it's proven and repeated by experiment/natural evidence.

In physics, we do know, far too many times "things looked they may be in a way" and then it turns out "yes maybe but it's all another thing really"

However I do know where one singularity of a black hole is, here in Wales .. (*)

A few days ago we almost were in a mono-dimensional time/space distorsion phase, just grey and fog all around a cloud of something and all the rest was gone.













(*) - note self censored for safety reasons -

[pogo]

What gravy said. In practice you do need to accelerate but that's certainly not implausible. If you accelerate at one gravity (10m/s^2) you reach lightspeed in 30 million seconds or just under a year. It takes an infinite amount of energy to reach lightspeed but you could come close, so you could spend a year accelerating, coast for 99 years, the decelerate for a year at the other end. The 99 years would feel like almost no time because of time dilation at near-light speeds. All highly theoretical though as we aren't close to developing a propulsion technology that can do this.

[Absolute_Zero]

Hi,

Can I ask another stupid physics question please.

Travel near the speed of light, for sake of argument "at". If a star was 100 light years away then is it correct to say that it would take you 100 years of time (from the perspective of the traveller) to reach it?

We pretty much covered this on page 4.

A photon, for an extreme example, travels from source to destination in zero time... from its point of view.

To wit you expressed surprise

Fuck!!!

[gravy]

Yeah I thought that was funny

Thanks of that comment because it made me go FUCK! as well

Ended up reading some very interesting stuff about neutrino decay and how a particle has to have mass to decay otherwise they have no time to do it in