what's going on guys welcome back this video is sponsored by ren
let's get into it i'm about to magically grow some hair back the progress is coming along
on the little tech startup that i told you guys about so here's my nice logo for the first one
the quantum computing related ones let me know if you can figure out the reference of the logo
in the comments down under uh with just that uh but that's all i'm going to say for now and
let's get back to the video an astrophysics phd candidate today i'm going to be checking
out some more physics youtube videos so i found a nice one on youtube let me just change this
make sure it's working all right let's check out this gravity visualized video i've never
seen it it's got 130 1 million views so if you're new around here make sure you subscribe
uh we talk about some physics occasionally let's get into it and so you put mass in a place of
space it warps space time and objects are not feeling a force of gravity they're just following
the natural curvature and so this is a sheet of lycra where do you get this is my old bike shorts
there's literally a spandex.com you can get a sheet like this if you buy the sales stuff
so you don't care what it looks like right uh for like 20 bucks maybe less depending on the
sale um and so you put matter and it works space-time and so if i have another object it also
says he should also say this is like imagining uh space-time as a 2d object you know flat sheet
whereas in reality space-time at least in einsteinian physics you know we say it's
for the object three spatial dimensions one time dimension so let's see what happens
once it plays they feel that and they're attracted
do each other and so that's that's okay this is being a very laggy apologies
and so you put matter and it works space-time and so if i have another object it also warps
space-time they feel that and they're attracted to each other and so that's that's einstein's
picture of gravity objects work space time feel that curvature and move accordingly
and if you have more mass
you have more mass it's going to
spend space-time more and so if you have objects there
also warp space-time they feel that and they're attracted to each other
and so that's that's einstein's picture of gravity objects work space time
feel that curvature and move accordingly and if you have more mass
you're right there you have more masses it's going to
spend space-time more and so if you have objects there
they are going to respond to that right and so you put something there
now it's attracted now in reality that big mass would feel the
warping of space-time by the marble too right it would move a little bit but we usually we usually
ignore that you know the earth makes the sun move a little bit but it's so small you can ignore it
the moon makes the earth kind of wobble around a point three quarters of the way from the center
of the earth we usually don't uh account for that when we're looking at satellite motion
well instead of just letting go of one what if i give it a sideways push
now it orbits now it's losing energy which wouldn't happen uh
in uh in the solar system right not noticeably there's some perturbations from other planets and
things but this one does lose energy and spirals in yeah it's losing energy due to the friction
of the spandex right but in space there's no no friction you know so but they the planet so
it what's yeah like you said the marble's losing energy spirals inwards uh but in our solar system
planets no friction so they don't lose any energy through their orbit however they do
lose a little bit of energy uh there's something called gravitational radiation
uh and if earth's still around in like 10 to the 20 years yeah it'll actually spiral into the song
if i don't push it as hard it will do an ellipse for a while anyway and let's get some more here
so one of the things i thought of to do with this is when you study the solar system
all the planets are growing around the sun the same way
why is that did god decide that he only like clockwise or depends on whether he's
above or below the solar system right uh why why is everything going in the same
direction well the answer is it wasn't different directions but there was a preferred direction
the disc that formed from had a slight preference one way versus another and things going the
opposite way got eliminated and when it's all said and done so everything's going the same
that was brilliant that usually that works 90 of the time is it like the toilet flushing
southern hemisphere wow can you do that again and so uh it won't work
and so i have slightly more in one hand than another but i don't consciously do that
and you want to give them so they spread out a little when you throw
it's it they're colliding with each other that you the ones the ones going up the wrong way get
eliminated right so cool now they're also i'm not saying that this analogy breaks down there's you
know another dimension right but those things are out of the plane also same thing happening
near the preferred plane also got eliminated i mean of course i i know about this phenomenon
but i've never seen it visualized like that in some sort of real demonstration
simulation called my solar system and so they've seen all this on the computer and when we do this
during our special relativity unit they're like hey it's just like the computer that's kind of
cool that a stretch sheet of lycra models things just like it but similar to the computer you might
be wondering like with the thing in the middle pulling down the sheet isn't it gravity causing
that like thing to go down so you know it's kind of like using gravity to explain gravity because
gravity is causing that shoot to go down but you know the key point is that um you know
matter in space-time will bend the fabric of space-time itself
some things we've discovered using this also it's just some larger marbles
so the earth moon system maybe
and so you can see that this seam you know you can't buy micro this big you get it in rolls and
you have to sew it together i've been told to use stretchy string stretchy thread to sew it
together and so the next time i do it i'll do that because it pulls and so you just a little bit of
thread fixes it and so uh in the morning when i first set this up i love it leaning against the
table i'll be underneath fixing holes from last year one time my principal walked in and i hear
somebody in the room and i'm underneath i'm in the middle of sewing and i'm not going to pause yet
and then he's looking around for me and he kind of knows somebody's in the room he's oh there
you are he goes what are you doing there and i go i'm repairing a rip in the fabric of space time
um another thing this does you've probably seen plastic ones of these
discovery uh center children's discovery museum in san jose has one the exploratorium has one
sometimes they have them as shopping malls to get you to put money in it
but one thing you can't do with those is put two masses in
nice and so when we went to the moon uh when we first started we sent our
spaceships on what are called free return trajectories so they would go to the moon this
is hard to get to happen and they would come back and like figure eight and so that lets you show
uh now of course the move is a lot smaller but if you look at the
uh plots of the free return trajectory back from the apollo program you'll see it has a figure
eight sort of shape and so this takes a little bit of practice to be able to do the figure eight
these clamps around here you can adjust it to make it tighter if it's not working
so steve and i when we set this up in the morning we played around with it and actually
i think it was working better than it usually is all of this so not easy to do
and so i go through that uh one year a kid who read some stuff about the dark energy
kind of like the opposite of gravity you don't know what it is just kind of in focus
and so i'm just thinking oh energy what is that that makes everything come apart
right and so dark energy you could get everyone on the edges and stretch it and so stuff
goes apart rather than toward it so if you can work in dark energy any time right with the kids
you know stuff they're not familiar with um and then i just let them play and so that's where we
discovered the earth moon thing is i just let them play and they're like mr burns come over
here look and uh they were all excited because they discovered that i said oh yeah it's good
and so there's you know then i just i throw out a few other things so they can
try this collected stuff over time and put out all the marbles
so uh so if you want to try it out but we do we probably want to get back to electricity magnetism
but we want to play mr burns now you might wonder if this is a good example of the galaxy as well
and it kind of is but it's kind of not because there's problems with galaxies and why uh they
even stay together and why they're not you know randomly you know stars flying off every which way
because it doesn't seem to be enough mass to hold them together and their rotation curve so
where the stars at the center of the galaxy are rotating around the quickest which is
as expected but as you go to the edges of say our spiral galaxy the stars that are rotating around
the galaxy should be doing so a lot slower but they're not it's actually kind of almost
constant and so the stars at the edge of the galaxy are absolutely blazing around the galaxy
and so where is this energy coming from you know why are they why is this happening well
this is one of the pieces of evidence for dark matter why we think there's a lot of dark matter
in galaxies so i'd say the whole thing if you bought all the parts and everything is
about a hundred dollars uh but one of my favorite days so you're gonna do it monday right stephen
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what a great teacher that was an awesome example we should do that for all young kids in primary
school i think i think people love seeing stuff like this so yeah i hope you guys enjoyed the
video let me know down under what you want me to react to next i'll catch you guys next time