Looking at faraway stuff - The Bear and Badger

SpaceGazelle

Oh this is a week old.

acemuzzy

Heh

cockbeard

Cheers SG wil look at those again, I think some new stuff stays less in my head as old stuff was there longer. It's bad but human

Vela

Even the oldest rocket launches are still amazing to watch. Don't worry about a week old video.

SpaceGazelle

I love this pic

cockbeard

Bye mate, have fun

superflyninja

Woah thats......insane. Vertigo inducing!

Dinostar77

SpaceGazelle wrote:

I love this pic

Amazing

SpaceGazelle

‘It may have been a small step for Neil, but it’s a heck of a big leap for me’.

https://www.theguardian.com/science/2017/dec/23/astronaut-bruce-mccandless-the-first-person-to-fly-freely-in-space-dies

SpaceGazelle

cockbeard wrote:

Cheers SG wil look at those again, I think some new stuff stays less in my head as old stuff was there longer. It's bad but human

I thought you might like this. Special relativity is really quite simple to derive, just remember small t is your time and Tau is their time.

And that really is it. All special relativity is just the time dilation, gamma. Everything else comes from this. You can see that the speed limit of the Universe is a simple consequence of geometry, or more precisely Pythagoras. As v approaches c, gamma tends to infinity and a person moving at the speed of light is frozen it time. speed = dist/time means that they are essentially going infinity fast, for them, and they can travel any distance in zero seconds.

Although the derivation is easy the consequences of Pythagoras can be a little harder to wrap your head around.

It's quite staggering how everything ties together, and when Maxwell united magnetism and electricity this weird constant popped out, and that was c. How can a Universal constant be a speed when all intertial frames are the same? Speed relative to what? And now we know, it's because of right-angled triangles and that speed is the same for everyone, so it really is a constant after all. I try not to dwell on the interconnectedness of all things because it makes me drink too much.

Vela

Hang on - if its geometry based, then does this itself constrain the possible curvature of the universe?
ie if its a consequence of the properties of right angle triangles (essentially) then the universe must be flat? Otherwise, if its not flat, c will vary over large distances [in a vacuum].

SpaceGazelle

Special Relativity is special because it only works in flat spacetime. General Relativity is an extension of special to include gravity (accelarated reference frames). It turns out if c stays the same everything else has to change (a cricket ball goes in a straight line through bent space) to accomodate this.

Einstein realised light would appear to curve in an accelerated reference frame, so if I aimed a torch at a point on the wall of an accelarating rocket it would appear to dip below that point because the rocket has moved on. Einstein interpreted this from the torch reference frame and realised that since you cant distinguish between acceleration and gravity maybe gravity is acceleration, and sure enough if you point a torch in a strong gravitational field the beam will curve. This is what is meant by curved space. You assume the beam is straight but the space is curved.

You can see how Einstein started to approach gravity as a geometric problem because of special relativity, and it was only when he was struggling with GR did he realise that special relativity was a very particular case and not the normal. Special wasn't named "Special" until after General was figured out.

SpaceGazelle

It's this btw that explains the cricket ball. There is no force on the ball and it's the ground (and players) that accelerate upwards to meet the ball. Yet the Earth isn't getting bigger, so that's why we say the space is curved. Curved spacetime is acceleration.

SpaceGazelle

Also, like in Special, clocks slow down in bent spacetime. You always take c to be constant and work from there, which is what Einstein did. Maxwell's equations gave us c. It just sort of pops out when you unify magnetism and electricity. It's a profounfd thing, having a constant that's a speed. It's the universe saying "there you go, deal with that if you dare", and Einstein took it at face value and now we can look for and indeed "see" a black hole.

SpaceGazelle

Einstein never came up with black holes btw and he didn't really believe in them at first, even though it was a consequence of his own theory. He did soon after and was just as astonished as anyone else to realise the things must exist.

Vela

Was it Chandrasekhar who theorised black holes?

I remember SR from uni, but completely forgot that the special bit applied to flat spacetime. Good explanation.

My only other memory of GR is utterly failing with tensors.

SpaceGazelle

It was Karl Schwarzschild of Schwarzschild Radius fame (radius of event horizon). Chandrasekhar won a Nobel prize for work on star evolution and the Chandraskhar limit is named him (size limit at which a star will turn into a BH when it dies - 1.4 Solar Masses).

cockbeard

One of the things that gets me, and it may be what Hawking was getting at in his late correction and retraction of previous work, is that whilst I've always understood uncertainty principle. Even in at macro scales it make logical sense, I always used the camera shutter speed analogy. Take a black hole though, might there be a point at which it has accrued so much mass that the gravity can no longer overcome the nuclear forces and it starts to push information back out again? Just a thought experiment I ran looking at another video the other day

edit: very likely that 'overcoming' nuclear forces is me mangling what I'm saying. Maybe it's because I don't see the tiny stuff as 'magical' (definitely weird though, trying to get head around higgs field creating mass) so I try to think of it as logical. Occam's razor in a sense. Anything that falls into a black hole still exists? We can't destroy or create stuff so even though it may well spin so tightly and so fast that we cannot see it, the stuff itself still exists from it's own perspective?

SpaceGazelle

Nobody understands the uncertainty principle. It makes no sense whatsoever and there's no known physical mechanism behind it. It's just the way it is.

SpaceGazelle

cockbeard wrote:

Anything that falls into a black hole still exists? We can't destroy or create stuff so even though it may well spin so tightly and so fast that we cannot see it, the stuff itself still exists from it's own perspective?

https://en.wikipedia.org/wiki/Black_hole_information_paradox

cockbeard

In the maths it's likely really mental, but it's obvious that if somethings moving you can either know where it is or where it's going but never both. I always guessed that's why it's always talked about in terms of probability
If I set a slow shutter speed I have a smear of a particle that smears from 1,1, through 3,3 ending at 5,5. With that information I can never know which of those points (or the infinite intermediaries) it is located at, however I could with very strong probability make a prediction that it will be at (6,6),(7,7),(n,n) at various points in the future, or (0,0),(-n,-n) at some points in the past??
If I set a fast shutter speed I have a crazy clear image of a particle at a specific point in space, however I can have zero knowledge of it's movement, therefore when it comes to the probability thing then yeah it could exist anywhere. It very likely won't, but who's to say it can't. On that thing though can we really tag specific particles, what's to say that movement isn't all like electrons through wire, in that marbles in a pipe rather than the same marble. Hmm, I'm rambling, but the passage of information rather than matter has to be cheaper surely, and isn't nature nothing if not efficient?

cockbeard

Hahaha, cheers SG, love you

SpaceGazelle

cockbeard wrote:

if somethings moving you can either know where it is or where it's going but never both.

This is true but it's because the two things don't exist at the same time in the same universe. A particle does not have a definite position AND a definite velocity. If it has a position it simply does not have a velocity, and by that I mean it's velocity does not exist. It literally doesn't have one, yet it's not staying still either.

Also, if you know an object's velocity that's fine but it no longer has a position in space. Again, literally. It's not that you can't measure the position, it literally does not have a position anywhere in the universe to measure. It exists nowhere but still exists.

Vela

In the case of known velocity, thought instead of having no position, it had every possible position?

SpaceGazelle

Yes, but that's the same thing. In this way it also has all the velocities when the position is known.

SpaceGazelle

These are the two extremes by the way. In practice you have probabilities of both, and when one goes up the other goes down, but it's important to know it's not a tech measurement issue.

Nature does this, one goes up and another goes down so there's a constant involved somewhere. Interestingly, everything moves through spacetime at the same speed. Light moves through max space and not through time and a stationary object moves through max time but not through space. One goes up, the other goes down. Constants everywhere.

SpaceGazelle

Moar Special Relativity.

Physics was in all sorts of trouble at the time, even though not many realised it. If you take a conductor and a magnet some very weird things happen. Move the magnet but keep the conductor still and a magnetic force occurs between them. Keep the magnet still and move the conductor and no magnetic force is felt. This is insane if all inertial frames are the same, and they have to be otherwise we no longer have consistent physical laws that apply to the universe and science is done for.

SR is the explanation, and the original paper is called On the Electrodynamics of Moving Bodies;

https://www.fourmilab.ch/etexts/einstein/specrel/specrel.pdf

For good measure that year Einstein also discovered quantum mechanics, proved the existence of these crazy things called atoms via explaining Brownian motion and developed his theory of mass and energy via E=mc2.

https://www.fourmilab.ch/etexts/einstein/E_mc2/e_mc2.pdf

Quite the year, 1905, even though nobody noticed for a while. Took 3 years for him to be offered an academic place somewhere iirc and the papers were published and largely forgotten about until their significance was understood a bit later on.

Dinostar77

https://www.independent.co.uk/life-style/gadgets-and-tech/news/universe-expanding-nasa-measurements-hubble-space-telescope-constant-a8886141.html

More problems with the Hubble constant. Universe is expanding faster than expected.

SpaceGazelle

It's a confirmation really that the early measurements were right about it accelerating.

SpaceGazelle

It's amusing to see the idea of the cosmological constant coming back around. Einstein invented it because he couldn't stand the idea of the non-static Universe that his own GR was predicting (other people did the maths and he refused to believe) so he invented the cosmological constant as this mysterious repulsive force that stopped the big crunch and held the universe apart for ever. He was wrong but sort of right as it's now being used in the theory of accelerated expansion instead.

Edit: Rather, he didn't invent it put it popped out of his GR equations as a thing that might exist.

Howdy, Stranger!

Categories