Black Holes, Navigation, The Big Crunch & Re-Entry Speeds: Your Cosmic Questions Answered |...

WEBVTT
Kind: captions
Language: en

00:00:00.320 --> 00:00:02.070
Hi there. Thanks for joining us once


00:00:02.080 --> 00:00:05.030
again. This is a Q&A edition of Space


00:00:05.040 --> 00:00:06.950
Nuts. My name is Andrew Dunley. Great to


00:00:06.960 --> 00:00:08.710
have your company. Uh we will be


00:00:08.720 --> 00:00:10.870
answering audience questions exclusively


00:00:10.880 --> 00:00:13.030
on this episode. We'll never do it


00:00:13.040 --> 00:00:15.669
again. Yes, we will. Uh we're going to


00:00:15.679 --> 00:00:19.830
be um looking at uh a concept that Ross


00:00:19.840 --> 00:00:22.390
has put up about black holes equaling


00:00:22.400 --> 00:00:24.630
dark matter. We'll uh we'll explain that


00:00:24.640 --> 00:00:26.630
or he will and we'll try and tear it


00:00:26.640 --> 00:00:29.750
apart. Uh Sandy is asking about


00:00:29.760 --> 00:00:33.830
navigation in space. Uh John is talking


00:00:33.840 --> 00:00:36.790
relativity, time, black holes, and the


00:00:36.800 --> 00:00:39.190
big crunch. I knew we'd get a question


00:00:39.200 --> 00:00:40.950
about the big crunch because we talked


00:00:40.960 --> 00:00:44.310
about it so recently. And the speed of


00:00:44.320 --> 00:00:46.790
re-entry is a question from Andy. We'll


00:00:46.800 --> 00:00:49.430
deal with all of that on this episode of


00:00:49.440 --> 00:00:50.470
Space Nuts.


00:00:50.480 --> 00:00:55.350
>> 15 seconds. Guidance is internal. 10 9


00:00:55.360 --> 00:00:57.110
ignition sequence start.


00:00:57.120 --> 00:00:57.990
>> Space nuts.


00:00:58.000 --> 00:01:00.549
>> 5 [music] 4 3 2


00:01:00.559 --> 00:01:02.950
>> 1 2 3 4 5 5 4 3 2 1


00:01:02.960 --> 00:01:04.149
>> Space Nuts


00:01:04.159 --> 00:01:06.630
>> astronauts report. It feels good.


00:01:06.640 --> 00:01:08.950
>> And with us once again is Professor Fred


00:01:08.960 --> 00:01:11.350
Watson, astronomer at large. Hello Fred.


00:01:11.360 --> 00:01:14.310
>> Hi Andrew. Good to talk again. Uh seems


00:01:14.320 --> 00:01:16.870
like only a few minutes ago that we were


00:01:16.880 --> 00:01:17.030
talking.


00:01:17.040 --> 00:01:19.030
>> It does, doesn't it? Yes. Extra.


00:01:19.040 --> 00:01:20.950
>> That's called relativity I think. Time


00:01:20.960 --> 00:01:21.670
dilation.


00:01:21.680 --> 00:01:23.350
>> Yeah. Um, I I'll tell you something


00:01:23.360 --> 00:01:25.030
funny. We we had our granddaughters


00:01:25.040 --> 00:01:26.630
around last night. They were supposed to


00:01:26.640 --> 00:01:27.749
stay the night, but they both


00:01:27.759 --> 00:01:29.590
chickenened out, so dad had to come and


00:01:29.600 --> 00:01:32.469
pick them up at 9:00, but um uh they


00:01:32.479 --> 00:01:34.390
were they were um having a bit of fun


00:01:34.400 --> 00:01:36.550
and um they like doing craft. And one of


00:01:36.560 --> 00:01:39.190
them built a telescope with a piece of


00:01:39.200 --> 00:01:41.109
paper out of and and was looking through


00:01:41.119 --> 00:01:42.870
it and Judy said, "What have you made?"


00:01:42.880 --> 00:01:45.109
And it was the four-year-old. She said,


00:01:45.119 --> 00:01:50.789
"I I I made a a looking through thing."


00:01:50.799 --> 00:01:52.230
That's what a telescope is. It's a


00:01:52.240 --> 00:01:54.469
looking through thing. [laughter] Um,


00:01:54.479 --> 00:01:56.230
which is nearly what they were


00:01:56.240 --> 00:01:58.870
originally called before the telescope


00:01:58.880 --> 00:02:00.310
was in 10. Yeah,


00:02:00.320 --> 00:02:01.830
>> she's ahead of her time.


00:02:01.840 --> 00:02:04.469
>> Device for seeing a device for seeing a


00:02:04.479 --> 00:02:05.510
far. [sighs]


00:02:05.520 --> 00:02:08.070
>> Yeah. Well, a looking through things.


00:02:08.080 --> 00:02:08.469
Yeah.


00:02:08.479 --> 00:02:09.669
>> Very cute.


00:02:09.679 --> 00:02:11.430
>> I love that. Yeah.


00:02:11.440 --> 00:02:12.790
>> I um [snorts]


00:02:12.800 --> 00:02:14.229
>> Yeah. You know, you know, you don't know


00:02:14.239 --> 00:02:16.070
what you might have, you know, released


00:02:16.080 --> 00:02:19.270
in that child's brain. She might become


00:02:19.280 --> 00:02:22.150
the next great astronomer using a


00:02:22.160 --> 00:02:24.070
looking through thing to make


00:02:24.080 --> 00:02:26.070
discoveries about the universe.


00:02:26.080 --> 00:02:27.750
>> Yeah. Yeah. Well, that's why we called


00:02:27.760 --> 00:02:30.790
it Vera. No, her name's uh her name's


00:02:30.800 --> 00:02:32.309
Felicity. [laughter]


00:02:32.319 --> 00:02:33.670
>> That's a good name as well. I like


00:02:33.680 --> 00:02:34.550
Felicity.


00:02:34.560 --> 00:02:36.229
>> It [snorts] is nice.


00:02:36.239 --> 00:02:39.030
>> Uh shall we get to our first question?


00:02:39.040 --> 00:02:40.550
>> Oh, all right.


00:02:40.560 --> 00:02:43.270
>> All right. Uh if black holes are the


00:02:43.280 --> 00:02:46.470
center of most galaxies uh and have been


00:02:46.480 --> 00:02:48.470
eating up matter almost from the


00:02:48.480 --> 00:02:50.790
beginning of the universe, can this be a


00:02:50.800 --> 00:02:53.589
possible explanation of dark matter? The


00:02:53.599 --> 00:02:57.270
black holes have eaten it. Now this uh


00:02:57.280 --> 00:03:00.070
comes from Ross Simon. I had to smile


00:03:00.080 --> 00:03:02.149
when I read his name because Ross Simon


00:03:02.159 --> 00:03:03.990
used to be a famous newsreader on the


00:03:04.000 --> 00:03:06.710
Australian Broadcasting Corporation's TV


00:03:06.720 --> 00:03:09.350
news service. I remember Ross, he was he


00:03:09.360 --> 00:03:11.190
was brilliant.


00:03:11.200 --> 00:03:13.030
might be the same one. You never know. I


00:03:13.040 --> 00:03:14.470
>> was going to say it's not the same Ross,


00:03:14.480 --> 00:03:15.509
is it? [laughter]


00:03:15.519 --> 00:03:18.309
>> I hope so. It would be lovely. But, uh,


00:03:18.319 --> 00:03:19.270
if it's not.


00:03:19.280 --> 00:03:21.910
>> Yeah. So, um, whether or not you are the


00:03:21.920 --> 00:03:24.869
famous Ross, Simon, Ross, lovely to hear


00:03:24.879 --> 00:03:28.390
from you. Uh, and, um, I mean, it's it's


00:03:28.400 --> 00:03:32.309
it is tempting, uh, to lump black holes


00:03:32.319 --> 00:03:34.789
and dark matter together. And indeed,


00:03:34.799 --> 00:03:37.509
um, that was looked at as being one of


00:03:37.519 --> 00:03:40.789
the first explanations of dark matter,


00:03:40.799 --> 00:03:43.030
uh, that we've got space full of black


00:03:43.040 --> 00:03:45.270
holes that we don't see because they're


00:03:45.280 --> 00:03:47.990
black holes, um, and that they might


00:03:48.000 --> 00:03:50.390
account for the dark matter. was the


00:03:50.400 --> 00:03:52.949
so-called macho theory, massive compact


00:03:52.959 --> 00:03:55.030
halo objects


00:03:55.040 --> 00:03:59.750
uh which was popular in the 80s


00:03:59.760 --> 00:04:02.869
um because it was only in the late '7s


00:04:02.879 --> 00:04:04.789
that people started taking the idea of


00:04:04.799 --> 00:04:07.509
dark matter seriously when we realized


00:04:07.519 --> 00:04:12.949
that um something like 80% of the matter


00:04:12.959 --> 00:04:16.710
in the universe is invisible to us. Uh


00:04:16.720 --> 00:04:18.310
now


00:04:18.320 --> 00:04:20.069
that's perhaps slightly different from


00:04:20.079 --> 00:04:22.150
what Ross is asking about because he's


00:04:22.160 --> 00:04:23.990
talking about material being sucked into


00:04:24.000 --> 00:04:28.710
black holes. Uh and that is certainly


00:04:28.720 --> 00:04:31.350
something that happens. But that's not


00:04:31.360 --> 00:04:33.990
matter that's missing. That's just gone.


00:04:34.000 --> 00:04:36.230
Uh the the bottom line is that the


00:04:36.240 --> 00:04:39.030
universe as we see it today has this


00:04:39.040 --> 00:04:41.189
mystery in that we know that there is


00:04:41.199 --> 00:04:43.510
stuff there that has a gravitational


00:04:43.520 --> 00:04:45.270
effect. It holds galaxies together. It


00:04:45.280 --> 00:04:48.150
holds galaxy clusters together, causes


00:04:48.160 --> 00:04:50.870
uh gravitational lensing all over the


00:04:50.880 --> 00:04:54.230
place. Um but we have no way of


00:04:54.240 --> 00:04:55.909
detecting what it is other than through


00:04:55.919 --> 00:04:58.629
its gravity. So it's it's some people


00:04:58.639 --> 00:05:00.629
used to call it missing matter. It's not


00:05:00.639 --> 00:05:03.350
missing. It's definitely there. uh this


00:05:03.360 --> 00:05:05.749
dark matter is around and it it's


00:05:05.759 --> 00:05:07.430
probably in the rooms that you and I are


00:05:07.440 --> 00:05:10.150
sitting in um at the moment uh because


00:05:10.160 --> 00:05:13.110
it it tends to be where normal matter is


00:05:13.120 --> 00:05:13.749
and we think


00:05:13.759 --> 00:05:15.510
>> Judy and I were actually talking about a


00:05:15.520 --> 00:05:17.670
dark matter the other day but you know I


00:05:17.680 --> 00:05:19.633
won't elaborate.


00:05:19.643 --> 00:05:20.710
[gasps]


00:05:20.720 --> 00:05:22.469
>> Well what you do in your spare time


00:05:22.479 --> 00:05:23.909
Andrew is [laughter]


00:05:23.919 --> 00:05:25.990
entirely up to you especially with your


00:05:26.000 --> 00:05:30.710
wife. Um um so yeah so so but um but the


00:05:30.720 --> 00:05:33.990
the the black hole thing did come in


00:05:34.000 --> 00:05:36.070
because of this theory back in the 80s


00:05:36.080 --> 00:05:38.870
that match massive compact halo objects


00:05:38.880 --> 00:05:42.550
objects that are kind of dead stars or


00:05:42.560 --> 00:05:44.629
orphan planets or more especially black


00:05:44.639 --> 00:05:47.909
holes might be uh the source of dark


00:05:47.919 --> 00:05:49.749
matter the source of this gravitation


00:05:49.759 --> 00:05:52.950
that we we see present in large on large


00:05:52.960 --> 00:05:54.790
scales like galaxy clusters and


00:05:54.800 --> 00:05:57.510
galaxies. What ruled that out uh was


00:05:57.520 --> 00:05:58.870
work carried out at a number of


00:05:58.880 --> 00:06:01.189
observatories including here uh in


00:06:01.199 --> 00:06:03.909
Australia uh in fact in a survey which


00:06:03.919 --> 00:06:06.790
was called Macho uh looking for these


00:06:06.800 --> 00:06:10.629
things uh and it was that if you if you


00:06:10.639 --> 00:06:12.469
had a universe full of black holes that


00:06:12.479 --> 00:06:14.870
you can't see you would still be able to


00:06:14.880 --> 00:06:16.950
detect them by what's called


00:06:16.960 --> 00:06:18.710
gravitational microlensing because


00:06:18.720 --> 00:06:20.150
occasionally one of these black holes


00:06:20.160 --> 00:06:22.629
would pass in front of a distant star


00:06:22.639 --> 00:06:24.550
and because black holes distort the


00:06:24.560 --> 00:06:27.029
space around that has behaves like a


00:06:27.039 --> 00:06:29.990
lens and you magnify the light of the


00:06:30.000 --> 00:06:32.629
distant star. So you you get a microl


00:06:32.639 --> 00:06:34.469
lensing event has a very characteristic


00:06:34.479 --> 00:06:37.510
shape. It's a star getting brighter uh


00:06:37.520 --> 00:06:39.990
to a sharp cusp and then fading away


00:06:40.000 --> 00:06:43.350
again quite symmetrically. Uh and they


00:06:43.360 --> 00:06:45.430
we do see them. They're caused by normal


00:06:45.440 --> 00:06:48.070
stars and and their planets. But in the


00:06:48.080 --> 00:06:50.629
numbers that you would have to have for


00:06:50.639 --> 00:06:54.230
black holes to be dark matter, they are


00:06:54.240 --> 00:06:56.469
not there. That they weren't enough. The


00:06:56.479 --> 00:06:58.469
numbers were far too low. And that's


00:06:58.479 --> 00:07:00.550
when the emphasis shifted to WIMPs, the


00:07:00.560 --> 00:07:02.870
weakly interacting massive particles,


00:07:02.880 --> 00:07:05.430
which is just one class of uh subatomic


00:07:05.440 --> 00:07:07.029
particles that we think dark matter


00:07:07.039 --> 00:07:08.870
might be. So that's where the theory


00:07:08.880 --> 00:07:12.550
stands at the moment. So black holes uh


00:07:12.560 --> 00:07:14.710
you know in the and and I think Ross is


00:07:14.720 --> 00:07:16.070
talking about super massive black holes


00:07:16.080 --> 00:07:17.589
at the centers of galaxies. Yes, they've


00:07:17.599 --> 00:07:19.830
been swallowing stuff up for 13.8


00:07:19.840 --> 00:07:22.469
billion years as far as we can tell. Um


00:07:22.479 --> 00:07:25.749
but they don't explain why today in


00:07:25.759 --> 00:07:28.070
today's universe um something like


00:07:28.080 --> 00:07:30.070
four-fifths of the m matter in the


00:07:30.080 --> 00:07:32.469
universe is invisible to us.


00:07:32.479 --> 00:07:35.189
>> Yeah. Um well there's so many things we


00:07:35.199 --> 00:07:37.990
don't understand and and and as yet uh


00:07:38.000 --> 00:07:39.990
which was brought up in a question


00:07:40.000 --> 00:07:43.029
recently, we have not been able to


00:07:43.039 --> 00:07:46.790
capture or identify a black uh a dark


00:07:46.800 --> 00:07:50.150
matter particle. So um yeah, until we


00:07:50.160 --> 00:07:53.270
can find some absolute proof and and


00:07:53.280 --> 00:07:56.070
study it, we we're probably going to


00:07:56.080 --> 00:07:58.150
>> just keep working with theory, I would


00:07:58.160 --> 00:08:01.270
imagine. Yeah, there's there are um


00:08:01.280 --> 00:08:03.830
techniques that can be brought to bear.


00:08:03.840 --> 00:08:07.909
Um one of the theories about dark matter


00:08:07.919 --> 00:08:11.589
is that if that while dark matter


00:08:11.599 --> 00:08:13.270
particles don't interact with normal


00:08:13.280 --> 00:08:15.029
matter particles, they may interact with


00:08:15.039 --> 00:08:16.950
each other. In other words, if you bring


00:08:16.960 --> 00:08:18.710
two dark matter particles together, it's


00:08:18.720 --> 00:08:20.629
thought they might annihilate and


00:08:20.639 --> 00:08:23.430
produce a signal in gamma radiation. So


00:08:23.440 --> 00:08:25.350
you get this flash of gamma rays which


00:08:25.360 --> 00:08:27.909
might have a characteristic spectrum.


00:08:27.919 --> 00:08:30.550
And people are looking for that


00:08:30.560 --> 00:08:34.389
phenomenon in the centers of galaxies


00:08:34.399 --> 00:08:36.230
because that's where you would expect


00:08:36.240 --> 00:08:38.310
the dark matter to be at its densest. So


00:08:38.320 --> 00:08:39.589
it's where you would expect the dark


00:08:39.599 --> 00:08:41.430
matter particles to interact with with


00:08:41.440 --> 00:08:44.149
each other. Um so far the results have


00:08:44.159 --> 00:08:46.310
been a bit mixed on that. But it's one


00:08:46.320 --> 00:08:49.269
possible way that we might eventually uh


00:08:49.279 --> 00:08:52.310
discover what dark matter is. May maybe


00:08:52.320 --> 00:08:55.350
maybe dark matter is like a negative


00:08:55.360 --> 00:08:57.509
photograph. Remember in the days of uh


00:08:57.519 --> 00:08:59.990
manual photography, you you'd take the


00:09:00.000 --> 00:09:01.750
film and it would be negative and then


00:09:01.760 --> 00:09:04.470
you turn it into the photograph.


00:09:04.480 --> 00:09:06.389
>> Maybe dark matter is the negative of the


00:09:06.399 --> 00:09:07.269
universe.


00:09:07.279 --> 00:09:11.590
>> Well, yeah. I mean, um you know, you


00:09:11.600 --> 00:09:14.630
there might well be a way that there is


00:09:14.640 --> 00:09:17.670
a sort of dark what can I call it? A


00:09:17.680 --> 00:09:22.710
dark particle physics. um um a whole uh


00:09:22.720 --> 00:09:27.110
sweep of subatomic particles which fall


00:09:27.120 --> 00:09:29.509
under what we lump together as dark


00:09:29.519 --> 00:09:30.949
matter. But it's not just a single


00:09:30.959 --> 00:09:32.470
particle. It's many different ones just


00:09:32.480 --> 00:09:34.310
like the particles of normal matter. The


00:09:34.320 --> 00:09:35.269
16


00:09:35.279 --> 00:09:38.230
>> uh normal matter part sorry 16 subatomic


00:09:38.240 --> 00:09:39.829
particles. They include forces as well


00:09:39.839 --> 00:09:41.910
as matter when you count the 16. But you


00:09:41.920 --> 00:09:43.829
know what I mean? You've got this this


00:09:43.839 --> 00:09:45.509
suite of different particles that make


00:09:45.519 --> 00:09:47.590
up normal matter. Maybe there's a suite


00:09:47.600 --> 00:09:49.350
of different particles that in some ways


00:09:49.360 --> 00:09:52.630
are a negative uh that make up um that


00:09:52.640 --> 00:09:56.230
make up dark matter. So I think that's


00:09:56.240 --> 00:09:57.750
we've been assuming it's just the one


00:09:57.760 --> 00:09:59.990
thing. It could be all sorts of things.


00:10:00.000 --> 00:10:01.590
>> Could be there could be, you know, they


00:10:01.600 --> 00:10:03.910
could be atoms and molecules made out of


00:10:03.920 --> 00:10:07.990
dark matter because they they interact


00:10:08.000 --> 00:10:09.509
with each other. I don't know it. Look,


00:10:09.519 --> 00:10:12.310
I'm not a particle physicist, but um the


00:10:12.320 --> 00:10:15.030
possibilities seem not exactly endless


00:10:15.040 --> 00:10:16.790
because particle physics has certain


00:10:16.800 --> 00:10:19.030
rules that you've got to follow. Uh but


00:10:19.040 --> 00:10:21.110
yeah, I I'm still pretty optimistic that


00:10:21.120 --> 00:10:22.470
we're going to get to the bottom of dark


00:10:22.480 --> 00:10:25.509
matter hopefully while I'm still alive


00:10:25.519 --> 00:10:28.630
cuz I want to know. Yeah, we all do. We


00:10:28.640 --> 00:10:30.550
all do. Uh thanks for the question,


00:10:30.560 --> 00:10:32.630
Ross. Uh really good discussion point.


00:10:32.640 --> 00:10:34.150
We get a lot of questions about dark


00:10:34.160 --> 00:10:36.389
matter and and black holes. Uh while


00:10:36.399 --> 00:10:37.910
we're on the subject of black holes,


00:10:37.920 --> 00:10:40.069
there was a an article released on the


00:10:40.079 --> 00:10:43.670
BBC uh early this year. Uh I know it's


00:10:43.680 --> 00:10:45.030
still early this year, but right, you


00:10:45.040 --> 00:10:47.030
know, I'm talking the 3rd of January,


00:10:47.040 --> 00:10:48.949
where scientists captured the first ever


00:10:48.959 --> 00:10:51.430
visual proof of two super massive black


00:10:51.440 --> 00:10:53.990
holes in a death spiral. So, we we're


00:10:54.000 --> 00:10:56.230
really starting to be able to find out


00:10:56.240 --> 00:10:59.670
more and more uh through our increased


00:10:59.680 --> 00:11:02.069
technology and the capacity to observe


00:11:02.079 --> 00:11:04.310
and and create images of these things.


00:11:04.320 --> 00:11:06.710
So, uh that was pretty exciting story. I


00:11:06.720 --> 00:11:07.910
read that one the other day. I thought


00:11:07.920 --> 00:11:10.949
I'd um give it a mention. But um yeah,


00:11:10.959 --> 00:11:14.470
they they uh of course uh the popular


00:11:14.480 --> 00:11:17.350
press uh created their own photo which


00:11:17.360 --> 00:11:19.030
has absolutely got nothing to do with


00:11:19.040 --> 00:11:20.870
it. [laughter] That's all right.


00:11:20.880 --> 00:11:23.990
>> But uh yeah, it sells the story, doesn't


00:11:24.000 --> 00:11:26.150
it? But uh yeah, they've got the image


00:11:26.160 --> 00:11:30.389
of these two black holes um basically


00:11:30.399 --> 00:11:31.990
getting ready to devour each other. I


00:11:32.000 --> 00:11:35.350
think the big one will win.


00:11:35.360 --> 00:11:36.310
>> Yes,


00:11:36.320 --> 00:11:37.269
>> probably. Well,


00:11:37.279 --> 00:11:38.230
>> thanks Ross.


00:11:38.240 --> 00:11:39.910
>> Yeah, probably.


00:11:39.920 --> 00:11:41.590
>> Yeah, thanks Ross. Good to hear from


00:11:41.600 --> 00:11:44.310
you.


00:11:44.320 --> 00:11:47.269
>> Okay, we checked all four systems and


00:11:47.279 --> 00:11:48.470
>> Space Nuts.


00:11:48.480 --> 00:11:53.190
>> Our next question comes from Sandy.


00:11:53.200 --> 00:11:54.790
>> Good day, Fred and Andrew. It's Sandy


00:11:54.800 --> 00:11:57.350
here from Melbourne again. Thanks for a


00:11:57.360 --> 00:12:00.069
cracking show as usual. Um, my question


00:12:00.079 --> 00:12:02.310
today is about navigation in the solar


00:12:02.320 --> 00:12:04.630
system for the various spacecraft that


00:12:04.640 --> 00:12:07.509
we've sent into deep space. Um, being a


00:12:07.519 --> 00:12:10.069
sci-fi nerd, my mind naturally goes to


00:12:10.079 --> 00:12:12.470
fancy graphics of star charts and orbit


00:12:12.480 --> 00:12:15.990
parts on a giant screen. However, wanted


00:12:16.000 --> 00:12:17.990
to ask how mission planners of various


00:12:18.000 --> 00:12:21.030
space agencies plot orbits. Do they take


00:12:21.040 --> 00:12:23.030
into account objects like asteroids for


00:12:23.040 --> 00:12:26.310
any close calls or is the space so vast


00:12:26.320 --> 00:12:28.870
it's not really necessary? Thanks,


00:12:28.880 --> 00:12:31.590
Heaps. Sandy, cheers.


00:12:31.600 --> 00:12:33.269
>> Thank you, Sandy. Uh, good to hear from


00:12:33.279 --> 00:12:34.310
you. I don't think we've heard from


00:12:34.320 --> 00:12:36.629
Sandy in a little while, but um yeah,


00:12:36.639 --> 00:12:41.590
he's um he he does a lot of great um


00:12:41.600 --> 00:12:44.150
astrophotography and he's got a a pretty


00:12:44.160 --> 00:12:46.230
amazing setup that he's he's shown me in


00:12:46.240 --> 00:12:48.550
the past about how he does it. Computers


00:12:48.560 --> 00:12:51.110
all plugged into telescopes and yeah,


00:12:51.120 --> 00:12:53.030
all this great software. It's a bit out


00:12:53.040 --> 00:12:55.829
of my league. Um I might get there one


00:12:55.839 --> 00:12:58.790
day. Uh navigation in space, plotting


00:12:58.800 --> 00:13:02.710
orbits, all that kind of jazz. Um I I


00:13:02.720 --> 00:13:05.110
must confess I struggle to get my head


00:13:05.120 --> 00:13:07.350
around it. Like it's not like driving a


00:13:07.360 --> 00:13:09.990
car. You've got to do um you know when


00:13:10.000 --> 00:13:12.550
it comes to space you've got um much


00:13:12.560 --> 00:13:15.910
less resistance, much more much more


00:13:15.920 --> 00:13:18.550
reaction to minute


00:13:18.560 --> 00:13:22.310
um thrust and micro thrust and all all


00:13:22.320 --> 00:13:23.590
sorts of other things. But you've got to


00:13:23.600 --> 00:13:25.750
be looking in all directions, not just,


00:13:25.760 --> 00:13:28.550
you know, on the plane of the planet


00:13:28.560 --> 00:13:30.949
when you're driving a car type of thing.


00:13:30.959 --> 00:13:32.550
I don't know what I'm trying to say, but


00:13:32.560 --> 00:13:35.350
um yeah, how how does it all work, Fred?


00:13:35.360 --> 00:13:39.030
>> Uh it's it's sort of the equivalent of


00:13:39.040 --> 00:13:40.949
plotting things on a screen, but not


00:13:40.959 --> 00:13:43.430
quite [clears throat] the same. Um but


00:13:43.440 --> 00:13:48.574
yeah, you know, the the uh idea that um


00:13:48.584 --> 00:13:51.030
[laughter] excuse me minute that I'm


00:13:51.040 --> 00:13:53.814
sorry, I've got this cough. Sandy's idea


00:13:53.824 --> 00:13:55.910
[clears throat] that we


00:13:55.920 --> 00:13:57.910
need to take into account I'm all right.


00:13:57.920 --> 00:14:00.310
I'm all right.


00:14:00.320 --> 00:14:02.790
Yeah, we need to take into account the


00:14:02.800 --> 00:14:04.150
positions of asteroids and things of


00:14:04.160 --> 00:14:06.710
that sort. That's exactly right. Um, so


00:14:06.720 --> 00:14:11.750
when you um chart uh a pathway


00:14:11.760 --> 00:14:14.069
through space, which is all done


00:14:14.079 --> 00:14:17.269
numerically, you know, it doesn't we can


00:14:17.279 --> 00:14:19.110
make displays of them and and I think


00:14:19.120 --> 00:14:22.150
people do as well, but the reality is


00:14:22.160 --> 00:14:24.710
that the real hardcore is locked up in


00:14:24.720 --> 00:14:27.030
the numbers and the equations. Um what


00:14:27.040 --> 00:14:30.310
you have to do is to uh at any instant


00:14:30.320 --> 00:14:32.629
along the orbit of the uh of the


00:14:32.639 --> 00:14:34.230
spacecraft because it is always an


00:14:34.240 --> 00:14:37.350
orbit. Uh usually for something like you


00:14:37.360 --> 00:14:38.710
know going between the planets it will


00:14:38.720 --> 00:14:41.509
be an orbit around the sun. Uh that's


00:14:41.519 --> 00:14:44.310
the way orbital mechanics work. Uh soon


00:14:44.320 --> 00:14:47.189
as you switch on your thrusters then you


00:14:47.199 --> 00:14:50.150
change that orbit. Uh but when all the


00:14:50.160 --> 00:14:52.230
thrusters are off and your main engines


00:14:52.240 --> 00:14:54.470
are off, you are following a trajectory


00:14:54.480 --> 00:14:58.150
which is essentially an orbit. Um not


00:14:58.160 --> 00:15:00.069
always a closed one. It could be an open


00:15:00.079 --> 00:15:01.829
orbit. Uh which is what's happening to


00:15:01.839 --> 00:15:03.829
the five spacecraft that are leaving the


00:15:03.839 --> 00:15:05.670
solar system.


00:15:05.680 --> 00:15:09.670
So uh but that orbit it's uh the future


00:15:09.680 --> 00:15:12.230
position of your spacecraft is dictated


00:15:12.240 --> 00:15:14.629
by the gravitational influence not just


00:15:14.639 --> 00:15:17.110
of the sun and the earth and probably


00:15:17.120 --> 00:15:19.189
the moon but all the planets. All of


00:15:19.199 --> 00:15:23.030
them exert a gravitational pull. Uh and


00:15:23.040 --> 00:15:25.509
um um that goes down to the asteroids as


00:15:25.519 --> 00:15:26.790
well. When you get if you're passing


00:15:26.800 --> 00:15:28.629
through the asteroid belt, you need to


00:15:28.639 --> 00:15:30.310
know where they all are. They would all


00:15:30.320 --> 00:15:32.150
all the ones which are known and there's


00:15:32.160 --> 00:15:35.110
more than a million known asteroids now.


00:15:35.120 --> 00:15:37.670
Uh you would have them kind of built


00:15:37.680 --> 00:15:40.389
into your software that's looking uh at


00:15:40.399 --> 00:15:42.069
the uh at the direction that your


00:15:42.079 --> 00:15:43.670
spacecraft is going in. If there was any


00:15:43.680 --> 00:15:46.389
risk of a collision, it would flag that


00:15:46.399 --> 00:15:47.750
and [clears throat] um it would also


00:15:47.760 --> 00:15:49.590
take into account the gravitational


00:15:49.600 --> 00:15:51.590
influence of any close encounters of


00:15:51.600 --> 00:15:54.470
asteroids. So it's it's a very precise


00:15:54.480 --> 00:15:58.150
science um as you know because we you


00:15:58.160 --> 00:16:01.030
know we know when for example the New


00:16:01.040 --> 00:16:05.030
Horizons uh flyby of Pluto a decade ago


00:16:05.040 --> 00:16:07.990
uh in 2015 um that the precision with


00:16:08.000 --> 00:16:10.550
which that was executed was unbelievable


00:16:10.560 --> 00:16:12.310
and it's because of orbital mechanics


00:16:12.320 --> 00:16:13.910
and how well we understand these


00:16:13.920 --> 00:16:16.230
gravitational influences uh that that


00:16:16.240 --> 00:16:19.430
let you do that. Um so uh yes space


00:16:19.440 --> 00:16:21.829
navigation in some ways it's easier uh


00:16:21.839 --> 00:16:25.030
than navigation on uh you know than


00:16:25.040 --> 00:16:26.870
driving a car because with driving a car


00:16:26.880 --> 00:16:28.870
you've always got to the predict


00:16:28.880 --> 00:16:31.110
unpredictability of the other road


00:16:31.120 --> 00:16:33.110
users. The great thing about orbital


00:16:33.120 --> 00:16:35.269
mechanics is you know what the other


00:16:35.279 --> 00:16:36.949
planets the other asteroids and all the


00:16:36.959 --> 00:16:39.531
rest of it are going to do. And ju just


00:16:39.541 --> 00:16:41.189
[clears throat] one other adjunct to


00:16:41.199 --> 00:16:44.790
this if I may. Um uh some years ago


00:16:44.800 --> 00:16:47.430
there was several papers which talked


00:16:47.440 --> 00:16:49.990
about the interplanetary superighway.


00:16:50.000 --> 00:16:52.710
Uh and these are effectively low energy


00:16:52.720 --> 00:16:54.790
trajectories between the planets and


00:16:54.800 --> 00:16:56.629
it's based on exactly what I've just


00:16:56.639 --> 00:16:59.430
been saying. You can map where um the


00:16:59.440 --> 00:17:02.069
gravitational pull of all the objects


00:17:02.079 --> 00:17:04.230
will take you. And it turned out that


00:17:04.240 --> 00:17:06.949
you can you if you can put um a


00:17:06.959 --> 00:17:08.789
spacecraft at one of your lrangee


00:17:08.799 --> 00:17:11.110
points, these gravitationally stable


00:17:11.120 --> 00:17:14.150
points, then leading from that are these


00:17:14.160 --> 00:17:16.069
various low energy pathways that take


00:17:16.079 --> 00:17:17.750
you to the the ground points of other


00:17:17.760 --> 00:17:19.669
planets. Uh and that's the


00:17:19.679 --> 00:17:21.829
interplanetary superighway. It might


00:17:21.839 --> 00:17:25.189
take you decades to get from uh from um


00:17:25.199 --> 00:17:28.309
you know from the Earth Lrange points to


00:17:28.319 --> 00:17:30.150
something like Mars's or Jupiter's


00:17:30.160 --> 00:17:32.549
Lrange points. It's a very slow process,


00:17:32.559 --> 00:17:36.070
but it it it does exist. This this


00:17:36.080 --> 00:17:37.909
almost like an imaginary highway which


00:17:37.919 --> 00:17:39.750
is changing all the time as the planets


00:17:39.760 --> 00:17:42.070
go around in their orbits. Uh just an


00:17:42.080 --> 00:17:43.590
interesting aspect of the of the


00:17:43.600 --> 00:17:45.190
navigation in space.


00:17:45.200 --> 00:17:49.110
>> Yeah, I imagine that a lot of this uh


00:17:49.120 --> 00:17:52.390
would be pre-programmed into the


00:17:52.400 --> 00:17:55.190
computers of these these vessels. Um


00:17:55.200 --> 00:17:58.070
they they do everything ahead of time


00:17:58.080 --> 00:18:00.230
cuz these these things are on autopilot.


00:18:00.240 --> 00:18:02.230
the the long haul spacecraft that are


00:18:02.240 --> 00:18:04.549
going out to do these missions.


00:18:04.559 --> 00:18:07.510
>> Uh so it would because and I've been in


00:18:07.520 --> 00:18:10.150
the cockpit of a a commercial uh


00:18:10.160 --> 00:18:13.190
airliner um long before you can't do


00:18:13.200 --> 00:18:15.190
that anymore, long before we had any


00:18:15.200 --> 00:18:17.350
issues like that. But um


00:18:17.360 --> 00:18:19.830
>> and and watching the process like the


00:18:19.840 --> 00:18:23.270
plane flies itself and the pilots sit


00:18:23.280 --> 00:18:25.029
back and tell dad jokes to the the


00:18:25.039 --> 00:18:27.607
tower. Um no, that's what happened.


00:18:27.617 --> 00:18:28.230
[laughter]


00:18:28.240 --> 00:18:30.710
But I I would imagine it's the same in


00:18:30.720 --> 00:18:32.230
space. All these things are


00:18:32.240 --> 00:18:35.190
pre-programmed, pre-calculated. Uh and


00:18:35.200 --> 00:18:37.990
then contingencies built in just in case


00:18:38.000 --> 00:18:39.430
something gets in the way that you


00:18:39.440 --> 00:18:42.950
didn't anticipate. Um they they modify


00:18:42.960 --> 00:18:45.830
the spacecraft to sense a problem and go


00:18:45.840 --> 00:18:49.909
around it. I I would imagine.


00:18:49.919 --> 00:18:53.510
>> Yeah. And in fact the you know the


00:18:53.520 --> 00:18:55.510
likelihood of something it's so


00:18:55.520 --> 00:18:59.909
predictable and our knowledge of of the


00:18:59.919 --> 00:19:02.950
of the sort of congestion in space if I


00:19:02.960 --> 00:19:06.710
can put it that way is so deep that um


00:19:06.720 --> 00:19:08.710
it's unlikely that something's going to


00:19:08.720 --> 00:19:10.470
come along to surprise you. You know you


00:19:10.480 --> 00:19:11.750
suddenly see something ahead that you've


00:19:11.760 --> 00:19:14.150
got to avoid. Uh because that avoidance


00:19:14.160 --> 00:19:16.549
might actually be very difficult. Uh you


00:19:16.559 --> 00:19:19.110
can you can do things. So perhaps the


00:19:19.120 --> 00:19:21.830
the the best example I can give you


00:19:21.840 --> 00:19:24.230
again it goes back to New Horizons and


00:19:24.240 --> 00:19:26.630
that is that once the Jupiter encounter


00:19:26.640 --> 00:19:29.270
sorry the Pluto encounter had happened


00:19:29.280 --> 00:19:32.549
uh back in July 2015


00:19:32.559 --> 00:19:35.350
um they looked for other potential


00:19:35.360 --> 00:19:39.510
targets and eventually found the object


00:19:39.520 --> 00:19:41.830
Arakov that was discovered as part of


00:19:41.840 --> 00:19:44.230
surveys looking for future targets and


00:19:44.240 --> 00:19:46.630
they worked out at what point they had


00:19:46.640 --> 00:19:49.909
to apply a thrust to the spacecraft to


00:19:49.919 --> 00:19:51.990
change its trajectory so that it would


00:19:52.000 --> 00:19:54.630
intersect with Araoth. And it and it all


00:19:54.640 --> 00:19:58.230
happened, you know, perfectly smoothly.


00:19:58.240 --> 00:20:00.310
Um I think it was a couple of years


00:20:00.320 --> 00:20:03.270
later when the Araoth uh flyby took


00:20:03.280 --> 00:20:04.950
place. I can't remember when it was,


00:20:04.960 --> 00:20:07.430
maybe even a bit later than that, maybe


00:20:07.440 --> 00:20:09.750
five years later. [clears throat] But um


00:20:09.760 --> 00:20:11.669
but that yeah, that that all happened.


00:20:11.679 --> 00:20:14.390
that was the the nearest thing to oh


00:20:14.400 --> 00:20:15.669
there's something ahead we need to


00:20:15.679 --> 00:20:17.990
change course to either interact with it


00:20:18.000 --> 00:20:20.150
or avoid it. Um and it was a very


00:20:20.160 --> 00:20:22.230
leisurely process and


00:20:22.240 --> 00:20:24.150
>> and you're right you're right about uh


00:20:24.160 --> 00:20:26.950
navigation on the planet on roads being


00:20:26.960 --> 00:20:28.549
much more dangerous. We were walking


00:20:28.559 --> 00:20:29.830
along the street the other day and


00:20:29.840 --> 00:20:31.750
somebody turned right off the main road


00:20:31.760 --> 00:20:35.029
into our uh into our part of town and


00:20:35.039 --> 00:20:37.270
>> uh went to the right hand side of the


00:20:37.280 --> 00:20:39.029
traffic island instead of the left right


00:20:39.039 --> 00:20:41.110
where we were walking.


00:20:41.120 --> 00:20:42.310
So


00:20:42.320 --> 00:20:44.310
>> yeah, I don't think she noticed to be


00:20:44.320 --> 00:20:45.990
honest. Honest, she just went up the


00:20:46.000 --> 00:20:48.470
wrong side of the road.


00:20:48.480 --> 00:20:50.950
>> Anyway, it happens. But we we always


00:20:50.960 --> 00:20:53.029
keep an eye out for that kind of thing.


00:20:53.039 --> 00:20:54.310
There you go, Sandy. Thanks for the


00:20:54.320 --> 00:20:56.950
question. The answer is easy peasy.


00:20:56.960 --> 00:20:58.310
Really [laughter]


00:20:58.320 --> 00:20:59.909
>> with modern computers.


00:20:59.919 --> 00:21:01.270
>> It's a lot harder if you're doing it by


00:21:01.280 --> 00:21:02.230
hand.


00:21:02.240 --> 00:21:03.510
>> Yes.


00:21:03.520 --> 00:21:05.110
>> All right. This is a Q&A edition of


00:21:05.120 --> 00:21:06.950
Space Nuts with Andrew Dunley and


00:21:06.960 --> 00:21:11.590
Professor Fred Watson.


00:21:11.600 --> 00:21:14.549
Space nuts. Okay, our next question


00:21:14.559 --> 00:21:18.310
comes from John in 27 parts. Hey guys,


00:21:18.320 --> 00:21:20.070
love the show. Every time I listen to a


00:21:20.080 --> 00:21:22.630
new episode, my mind goes crazy thinking


00:21:22.640 --> 00:21:24.470
about new possibilities and questions. I


00:21:24.480 --> 00:21:28.390
have two questions about time dilation.


00:21:28.400 --> 00:21:31.350
Uh in general relativity, uh if general


00:21:31.360 --> 00:21:33.830
re relativity causes time to be observed


00:21:33.840 --> 00:21:35.830
at different rates,


00:21:35.840 --> 00:21:38.070
would that mean someone orbiting very


00:21:38.080 --> 00:21:40.710
close to one of the first black holes in


00:21:40.720 --> 00:21:42.549
existence would experience a universe


00:21:42.559 --> 00:21:45.270
that has existed for a much shorter


00:21:45.280 --> 00:21:47.190
period of time?


00:21:47.200 --> 00:21:50.549
Uh, as a follow-up to this, if the new


00:21:50.559 --> 00:21:52.710
theory about the big crunch turns out to


00:21:52.720 --> 00:21:56.630
be true, would the finite time of the


00:21:56.640 --> 00:22:00.789
universe form the big bang to uh uh from


00:22:00.799 --> 00:22:02.549
the big bang to the big crunch be


00:22:02.559 --> 00:22:05.430
considerably shorter if again you were


00:22:05.440 --> 00:22:08.310
orbiting close to a black hole? Uh we


00:22:08.320 --> 00:22:11.590
see the universe as being 13.79


00:22:11.600 --> 00:22:14.470
billion years old and uh new estimates


00:22:14.480 --> 00:22:17.750
put the big crunch at 20 billion years


00:22:17.760 --> 00:22:20.070
into the future. My brain hurts thinking


00:22:20.080 --> 00:22:21.909
that these time scales could be


00:22:21.919 --> 00:22:23.510
considerably different due to time


00:22:23.520 --> 00:22:25.990
dilation. All the best uh John from


00:22:26.000 --> 00:22:29.029
Suffach in the UK. [gasps]


00:22:29.039 --> 00:22:31.350
>> Oh, there's a lot in there.


00:22:31.360 --> 00:22:35.350
Um yeah and and so it's it's quite


00:22:35.360 --> 00:22:39.110
complicated because time dilation uh


00:22:39.120 --> 00:22:41.830
depends on your vantage point.


00:22:41.840 --> 00:22:43.669
>> So yeah, if you're in orbit around a


00:22:43.679 --> 00:22:46.230
black hole uh you're in an intense


00:22:46.240 --> 00:22:48.070
gravitational field.


00:22:48.080 --> 00:22:50.470
>> You're also stuffed, but we'll just deal


00:22:50.480 --> 00:22:52.230
with that another time.


00:22:52.240 --> 00:22:52.870
[sighs and gasps]


00:22:52.880 --> 00:22:57.750
>> Um yeah, you're you experience time just


00:22:57.760 --> 00:22:59.430
at the normal rate.


00:22:59.440 --> 00:23:04.630
>> Yeah. um what uh what um an outside


00:23:04.640 --> 00:23:06.630
observer looking at you would see would


00:23:06.640 --> 00:23:08.950
be your time going very slowly. The time


00:23:08.960 --> 00:23:10.870
would be dilated.


00:23:10.880 --> 00:23:14.390
>> So um I I suppose what we're talking


00:23:14.400 --> 00:23:17.990
about here is that in terms of the what


00:23:18.000 --> 00:23:19.750
you might call the frame of rest of the


00:23:19.760 --> 00:23:22.070
universe itself.


00:23:22.080 --> 00:23:26.470
uh that's what we what we see when we


00:23:26.480 --> 00:23:28.070
look at the universe in general and


00:23:28.080 --> 00:23:31.350
that's what gives us the 13.79 or 13.8


00:23:31.360 --> 00:23:35.110
billion year age of the universe um your


00:23:35.120 --> 00:23:37.430
perception of that so that time


00:23:37.440 --> 00:23:39.990
effectively wouldn't change uh but your


00:23:40.000 --> 00:23:41.669
perception of it if you were in orbit


00:23:41.679 --> 00:23:43.350
around the black hole would it would


00:23:43.360 --> 00:23:45.430
probably appear to look as though it was


00:23:45.440 --> 00:23:48.230
going very quickly uh but that's cuz


00:23:48.240 --> 00:23:53.750
your time's slower. uh and likewise um


00:23:53.760 --> 00:23:56.149
uh with the you know the density of the


00:23:56.159 --> 00:23:59.430
universe being higher uh at earlier


00:23:59.440 --> 00:24:01.750
stages. Yes, we we do know time dilation


00:24:01.760 --> 00:24:03.110
takes place. You can you can actually


00:24:03.120 --> 00:24:07.669
see that uh because um when uh


00:24:07.679 --> 00:24:11.110
scientists look at the light curves of


00:24:11.120 --> 00:24:13.430
supernovi exploding stars, they have a


00:24:13.440 --> 00:24:15.430
light curve, their light increases and


00:24:15.440 --> 00:24:18.950
then decreases uh in a more gradual way


00:24:18.960 --> 00:24:21.510
with a very characteristic shape. Uh


00:24:21.520 --> 00:24:24.070
those light curves are dilated. They're


00:24:24.080 --> 00:24:26.310
stretched when we look at ones in the


00:24:26.320 --> 00:24:28.870
early universe. So the phenomenon does


00:24:28.880 --> 00:24:32.630
happen but um it doesn't happen at a


00:24:32.640 --> 00:24:34.710
level that's going to significantly


00:24:34.720 --> 00:24:37.750
shorten our um perception you know the


00:24:37.760 --> 00:24:39.990
the universe's perception of its of its


00:24:40.000 --> 00:24:41.750
own history if I put it that way. I


00:24:41.760 --> 00:24:43.350
think I'm talking a little bit in


00:24:43.360 --> 00:24:45.909
riddles here but I hope John follows me


00:24:45.919 --> 00:24:49.029
that it it really is all about your um


00:24:49.039 --> 00:24:50.630
your frame of rest as we call it your


00:24:50.640 --> 00:24:53.350
vantage point uh on the universe because


00:24:53.360 --> 00:24:55.029
that's what time dilation is all about.


00:24:55.039 --> 00:24:57.269
It's about people seeing time going


00:24:57.279 --> 00:24:58.630
differently depending on their


00:24:58.640 --> 00:25:01.669
viewpoint. Our viewpoint here uh from


00:25:01.679 --> 00:25:04.549
earth is probably that of the universe


00:25:04.559 --> 00:25:07.590
of a as a whole effectively uh because


00:25:07.600 --> 00:25:09.909
we are not in an intense gravitational


00:25:09.919 --> 00:25:12.630
field. It the gravitational field of the


00:25:12.640 --> 00:25:14.789
sun is the strongest thing we feel that


00:25:14.799 --> 00:25:16.710
keeps the the earth in orbit but it's


00:25:16.720 --> 00:25:18.470
it's nothing like what you would find


00:25:18.480 --> 00:25:20.789
around a black hole. And so we've got


00:25:20.799 --> 00:25:24.549
probably a fairly unbiased view of the


00:25:24.559 --> 00:25:26.870
universe and its history. Now,


00:25:26.880 --> 00:25:29.990
>> are we in a gravity well?


00:25:30.000 --> 00:25:31.669
>> Yeah, we are. I mean, the the earth


00:25:31.679 --> 00:25:33.830
itself creates a gravity well. Uh, and


00:25:33.840 --> 00:25:35.990
that's what keeps us stuck to the earth


00:25:36.000 --> 00:25:39.190
because the gravitational potential at


00:25:39.200 --> 00:25:41.190
your head is a little bit different from


00:25:41.200 --> 00:25:43.350
what it is at your feet. And that's


00:25:43.360 --> 00:25:45.190
what's pulling you down, the changing


00:25:45.200 --> 00:25:46.470
shape of space.


00:25:46.480 --> 00:25:48.630
>> There you go. All right. Um,


00:25:48.640 --> 00:25:50.549
>> I'm not spaghettifying you.


00:25:50.559 --> 00:25:54.710
>> No. No. So, um, did we unpack everything


00:25:54.720 --> 00:25:57.990
there? [laughter]


00:25:58.000 --> 00:25:59.830
>> Yeah, I think so. I think we I think we


00:25:59.840 --> 00:26:00.789
covered most of it.


00:26:00.799 --> 00:26:02.070
>> Okay. Um,


00:26:02.080 --> 00:26:04.710
>> look, I know.


00:26:04.720 --> 00:26:05.830
>> Sorry. Go ahead.


00:26:05.840 --> 00:26:07.350
>> No, I was going to say that he also


00:26:07.360 --> 00:26:10.310
asked if the big crunch would happen


00:26:10.320 --> 00:26:12.789
faster than the expansion.


00:26:12.799 --> 00:26:15.110
>> So, yes. So that I kind of you know lump


00:26:15.120 --> 00:26:17.190
that into the the fact that the the


00:26:17.200 --> 00:26:19.350
times that we observe from our


00:26:19.360 --> 00:26:21.830
>> location in the universe probably yes 20


00:26:21.840 --> 00:26:23.430
billion years down the track seems about


00:26:23.440 --> 00:26:25.430
right for the big crunch if if the


00:26:25.440 --> 00:26:27.669
recent desi results yeah it's what


00:26:27.679 --> 00:26:28.710
happens


00:26:28.720 --> 00:26:33.590
>> um um uh I was going to say that like


00:26:33.600 --> 00:26:36.070
you John uh these things make my brain


00:26:36.080 --> 00:26:38.710
hurt so um don't think it's it's


00:26:38.720 --> 00:26:42.950
peculiar to uh to um to a few people we


00:26:42.960 --> 00:26:45.269
I think I think most physicists, you


00:26:45.279 --> 00:26:47.590
know, they get their they really have to


00:26:47.600 --> 00:26:50.630
get their heads around the things like


00:26:50.640 --> 00:26:52.310
seeing pe seeing things from different


00:26:52.320 --> 00:26:54.549
vantage points. It's not entire it's not


00:26:54.559 --> 00:26:56.310
intuitive at all.


00:26:56.320 --> 00:26:59.029
>> No. No. All right, John. Thank you. And


00:26:59.039 --> 00:27:01.269
I hope all is well in Suffach. That's uh


00:27:01.279 --> 00:27:04.549
that's basically what one of one of the


00:27:04.559 --> 00:27:06.230
eastern most points of England, isn't


00:27:06.240 --> 00:27:06.630
it?


00:27:06.640 --> 00:27:09.590
>> I used to live in Suffach. But uh yeah,


00:27:09.600 --> 00:27:11.990
not not far from Cambridge, which is in


00:27:12.000 --> 00:27:14.470
Cambridge High, but SuffK I was over the


00:27:14.480 --> 00:27:17.110
border in Suffach. You're right. SuffK,


00:27:17.120 --> 00:27:18.950
Norfolk and Suffach are the two counties


00:27:18.960 --> 00:27:21.269
in East Anglia, that sort of


00:27:21.279 --> 00:27:23.269
semic-ircular bit that sticks out not


00:27:23.279 --> 00:27:26.070
very much north of the Temp's Estie.


00:27:26.080 --> 00:27:27.029
>> There you go. All right.


00:27:27.039 --> 00:27:28.950
>> Very pretty country. Yeah.


00:27:28.960 --> 00:27:31.830
>> Yes. Good to hear from you. Our final


00:27:31.840 --> 00:27:35.830
question today comes from Andy.


00:27:35.840 --> 00:27:38.230
>> Hi guys, this is Andy from London. I'm a


00:27:38.240 --> 00:27:40.390
new listener to your podcast and quite


00:27:40.400 --> 00:27:42.950
new to science, so forgive me if this is


00:27:42.960 --> 00:27:45.110
a stupid question, but I was just


00:27:45.120 --> 00:27:48.149
wondering um when craft re-enter


00:27:48.159 --> 00:27:49.990
atmosphere and they have to come in at a


00:27:50.000 --> 00:27:54.310
certain angle to stop from burning up um


00:27:54.320 --> 00:27:56.789
why do the not just come through slowly


00:27:56.799 --> 00:28:00.549
to to get away with the friction effect


00:28:00.559 --> 00:28:04.710
which uh causes the heat? Thanks.


00:28:04.720 --> 00:28:06.870
>> Thank you, Andy. Um, and thanks for


00:28:06.880 --> 00:28:08.549
finding Space Nuts and being a new


00:28:08.559 --> 00:28:11.990
listener. Um, you've only got 590 odd


00:28:12.000 --> 00:28:15.029
episodes to catch up now. So, um, yeah,


00:28:15.039 --> 00:28:16.789
have [clears throat] fun with that. Uh,


00:28:16.799 --> 00:28:19.510
we've certainly had fun with it. Um, I


00:28:19.520 --> 00:28:21.110
think we've had this question before,


00:28:21.120 --> 00:28:27.190
maybe asked a different way. Um,


00:28:27.200 --> 00:28:29.669
and and when it comes to a spacecraft,


00:28:29.679 --> 00:28:31.110
we're orbiting the planet, which is


00:28:31.120 --> 00:28:32.630
essentially it's just constantly


00:28:32.640 --> 00:28:34.230
falling. you're just maintaining a


00:28:34.240 --> 00:28:38.470
velocity that stops you falling in. Um,


00:28:38.480 --> 00:28:41.590
you do have to slow down to re-enter so


00:28:41.600 --> 00:28:46.149
that that arc is is, you know, reduced


00:28:46.159 --> 00:28:47.909
or increased. Can't remember which. Uh,


00:28:47.919 --> 00:28:49.909
and and then you fall through the


00:28:49.919 --> 00:28:53.110
atmosphere. Um, you can't stop and just


00:28:53.120 --> 00:28:56.070
sort of ease your way back in as against


00:28:56.080 --> 00:28:58.630
a space elevator which would be able to


00:28:58.640 --> 00:29:02.230
do that if we ever build one. But that's


00:29:02.240 --> 00:29:04.789
a different set of but a space elevator


00:29:04.799 --> 00:29:07.830
is essentially not orbiting. It is


00:29:07.840 --> 00:29:09.669
stationary to a point on the planet


00:29:09.679 --> 00:29:12.230
which means it goes up and down. Is that


00:29:12.240 --> 00:29:13.750
making sense?


00:29:13.760 --> 00:29:16.789
>> Yeah. Um yes it is. [laughter]


00:29:16.799 --> 00:29:18.630
That's good. That's the first time ever.


00:29:18.640 --> 00:29:20.950
>> Everything you've said is correct. Um


00:29:20.960 --> 00:29:24.389
space elevators uh hypothesized Buzz


00:29:24.399 --> 00:29:26.630
Aldrin told me uh that night I had


00:29:26.640 --> 00:29:27.990
dinner with him it's never going to


00:29:28.000 --> 00:29:29.909
happen. And he he was quite right


00:29:29.919 --> 00:29:32.070
because um the space elevator has to sit


00:29:32.080 --> 00:29:33.430
on the equator.


00:29:33.440 --> 00:29:35.510
>> Uh every spacecraft in the sky crosses


00:29:35.520 --> 00:29:37.029
the equator. So you're always going to


00:29:37.039 --> 00:29:39.830
get things banging into it. Uh it would


00:29:39.840 --> 00:29:42.149
be very difficult to build one. Uh you


00:29:42.159 --> 00:29:44.149
know apart from the structural thing. Uh


00:29:44.159 --> 00:29:46.630
so neglecting the space elevator for a


00:29:46.640 --> 00:29:48.149
minute, what you said is absolutely


00:29:48.159 --> 00:29:50.870
right. In order to stay in orbit, you


00:29:50.880 --> 00:29:53.029
have to achieve basically a horizontal


00:29:53.039 --> 00:29:56.675
velocity of about 8 kilometers/s.


00:29:56.685 --> 00:29:56.950
>> [gasps]


00:29:56.960 --> 00:29:59.750
>> uh and that's otherwise you just fall


00:29:59.760 --> 00:30:03.269
back to earth. So that's what all the


00:30:03.279 --> 00:30:05.909
you know the the the huge amount of fuel


00:30:05.919 --> 00:30:07.909
that is carried by a rocket being


00:30:07.919 --> 00:30:09.990
launched that's what it's all about.


00:30:10.000 --> 00:30:12.549
It's about getting up to a height of two


00:30:12.559 --> 00:30:15.669
or 300 kilometers and getting that


00:30:15.679 --> 00:30:17.750
orbital velocity getting that horizontal


00:30:17.760 --> 00:30:20.310
velocity of 8 kilometers/s.


00:30:20.320 --> 00:30:25.510
So, um, what you could do, uh, is, and


00:30:25.520 --> 00:30:28.070
and you know, going, this is hopefully


00:30:28.080 --> 00:30:32.310
help helping Andy, uh, if you had


00:30:32.320 --> 00:30:35.430
unlimited amounts of fuel, you could


00:30:35.440 --> 00:30:37.750
turn the rocket round, uh, from its


00:30:37.760 --> 00:30:41.430
orbital position and fire uh, your


00:30:41.440 --> 00:30:44.230
rockets to act as a braking system to


00:30:44.240 --> 00:30:45.990
slow the thing down. And then you could


00:30:46.000 --> 00:30:47.830
gently tiptoe down through the


00:30:47.840 --> 00:30:49.909
atmosphere, constantly firing your


00:30:49.919 --> 00:30:53.029
rockets. It's actually what um Musk does


00:30:53.039 --> 00:30:56.630
with his with his uh Falcon rockets. He


00:30:56.640 --> 00:30:59.190
he he's got enough fuel left that he can


00:30:59.200 --> 00:31:01.750
bring the empty spacecraft back down


00:31:01.760 --> 00:31:05.029
intact uh and and use it again uh


00:31:05.039 --> 00:31:08.950
without needing a heat shield. Um so you


00:31:08.960 --> 00:31:11.750
could do that. Uh and he's demonstrated


00:31:11.760 --> 00:31:15.750
that we can. Uh but it turns out that uh


00:31:15.760 --> 00:31:19.110
it's much more effective to use this


00:31:19.120 --> 00:31:21.510
process called aerobreing where you


00:31:21.520 --> 00:31:24.230
actually use the atmosphere itself to


00:31:24.240 --> 00:31:27.269
slow the spacecraft down. Uh because you


00:31:27.279 --> 00:31:28.789
don't need any fuel for that. You just


00:31:28.799 --> 00:31:30.149
need something that's going to stop it


00:31:30.159 --> 00:31:32.549
burning up. Uh so getting from this 8


00:31:32.559 --> 00:31:34.149
kilometers/s


00:31:34.159 --> 00:31:37.190
down to a few, you know, a meter or two


00:31:37.200 --> 00:31:39.430
per second uh for a splashdown or a


00:31:39.440 --> 00:31:42.630
touchdown uh is the tricky bit. And


00:31:42.640 --> 00:31:45.269
you've got to uh you know you you you


00:31:45.279 --> 00:31:47.750
you've got to use whatever means are at


00:31:47.760 --> 00:31:49.750
your disposal and the easiest one is


00:31:49.760 --> 00:31:51.269
arrow braingreaking using the atmosphere


00:31:51.279 --> 00:31:53.509
itself to slow you down. I should point


00:31:53.519 --> 00:31:55.990
out that um I think the first stage


00:31:56.000 --> 00:31:57.830
Falcon rockets they're not at orbital


00:31:57.840 --> 00:32:00.230
velocity uh when they turn around and


00:32:00.240 --> 00:32:02.149
come back. They haven't got up to that 8


00:32:02.159 --> 00:32:04.149
kilometers/s because there's a second


00:32:04.159 --> 00:32:06.549
stage that lets them do that and they


00:32:06.559 --> 00:32:09.029
still burn up basically coming back into


00:32:09.039 --> 00:32:13.190
the atmosphere. the second stages.


00:32:13.200 --> 00:32:14.950
>> Good question. Not a stupid question at


00:32:14.960 --> 00:32:15.269
all.


00:32:15.279 --> 00:32:19.110
>> No. No. And and you know,


00:32:19.120 --> 00:32:22.149
it's rocket science. I mean, we we often


00:32:22.159 --> 00:32:24.389
say when something's not difficult, it's


00:32:24.399 --> 00:32:25.909
not rocket science. This is rocket


00:32:25.919 --> 00:32:29.269
science. Um orbital speeds are


00:32:29.279 --> 00:32:32.149
significant. They're they're to stay out


00:32:32.159 --> 00:32:36.630
there. They've got to um do 17,000 mph,


00:32:36.640 --> 00:32:38.149
>> which is 8 kilometers/ second.


00:32:38.159 --> 00:32:42.070
>> Yeah. Mark 25. Um, to slow down so that


00:32:42.080 --> 00:32:44.389
you can return to Earth safely, you've


00:32:44.399 --> 00:32:47.269
got to go from that speed to subsonic


00:32:47.279 --> 00:32:48.230
speed.


00:32:48.240 --> 00:32:49.029
>> Yeah.


00:32:49.039 --> 00:32:51.669
>> And using fuel to do that would be


00:32:51.679 --> 00:32:52.470
exhaustive.


00:32:52.480 --> 00:32:54.149
>> Yeah, that's right. That's exactly


00:32:54.159 --> 00:32:57.029
right. You know, you basically you're


00:32:57.039 --> 00:33:00.710
looking at the same amount of hardware


00:33:00.720 --> 00:33:03.509
in terms of a rocket and its fuel to to


00:33:03.519 --> 00:33:05.110
get you up there. you'd need the same


00:33:05.120 --> 00:33:07.509
amount to bring you back just to do a


00:33:07.519 --> 00:33:10.070
gentle touchdown on the earth.


00:33:10.080 --> 00:33:13.830
>> Um uh notwithstanding the first stage


00:33:13.840 --> 00:33:15.750
recovery that we're starting to see with


00:33:15.760 --> 00:33:17.269
well not starting they've been doing it


00:33:17.279 --> 00:33:21.190
for 10 years with the Falcon 9 rockets.


00:33:21.200 --> 00:33:23.110
>> Yeah. Uh I'm sure the technology will


00:33:23.120 --> 00:33:25.110
improve and we'll find better ways but


00:33:25.120 --> 00:33:27.269
at the moment using the atmosphere as a


00:33:27.279 --> 00:33:28.630
free braking system.


00:33:28.640 --> 00:33:29.590
>> Yeah. Yeah.


00:33:29.600 --> 00:33:31.430
>> Yeah. Works really well.


00:33:31.440 --> 00:33:31.750
>> It does.


00:33:31.760 --> 00:33:33.190
>> Except when it doesn't. But that's only


00:33:33.200 --> 00:33:34.549
happened a couple of times.


00:33:34.559 --> 00:33:35.190
>> Yeah, it is.


00:33:35.200 --> 00:33:36.870
>> Um, yeah. [sighs]


00:33:36.880 --> 00:33:38.549
Thank you, Andy. Great question, though.


00:33:38.559 --> 00:33:40.389
Uh, really appreciate it. And don't


00:33:40.399 --> 00:33:41.909
forget, if you've got questions for us,


00:33:41.919 --> 00:33:44.070
you can send them through via our


00:33:44.080 --> 00:33:46.389
website, spacenutspodcast.com,


00:33:46.399 --> 00:33:48.630
spacenuts.io. You click on the little


00:33:48.640 --> 00:33:51.750
AMA link at the top. Uh, which means ask


00:33:51.760 --> 00:33:54.230
me anything. I finally figured that out.


00:33:54.240 --> 00:33:57.110
Ask me anything. AMA. Uh, and you just


00:33:57.120 --> 00:33:58.950
fill in the blanks. whether it's a text


00:33:58.960 --> 00:34:00.710
question or you can hit the start


00:34:00.720 --> 00:34:03.110
recording button and record a question


00:34:03.120 --> 00:34:06.389
for us. Um, any device with a microphone


00:34:06.399 --> 00:34:08.629
will do. spacenutspodcast.com or


00:34:08.639 --> 00:34:10.710
spacenuts.io.


00:34:10.720 --> 00:34:12.069
Uh, while you're there, you might want


00:34:12.079 --> 00:34:14.230
to hit the supporter button and um, you


00:34:14.240 --> 00:34:17.109
know, look at ways of supporting us uh,


00:34:17.119 --> 00:34:19.990
financially. It is not essential. We do


00:34:20.000 --> 00:34:22.629
not demand that of you. Never will. But


00:34:22.639 --> 00:34:24.310
uh, we do have a lot of people who


00:34:24.320 --> 00:34:26.389
volunteer to do that. In fact, it was


00:34:26.399 --> 00:34:27.990
the listener's idea in the first place


00:34:28.000 --> 00:34:29.829
to set that up for us. We didn't even


00:34:29.839 --> 00:34:31.430
think about it until someone said, "How


00:34:31.440 --> 00:34:33.829
do I contribute to the program?" And it


00:34:33.839 --> 00:34:36.310
all took off from there. Um, and we do


00:34:36.320 --> 00:34:38.710
appreciate our supporters very very


00:34:38.720 --> 00:34:41.589
much. Uh, thank you so much for thinking


00:34:41.599 --> 00:34:43.510
enough of us to put a couple of bucks


00:34:43.520 --> 00:34:46.069
behind um behind our words. We we


00:34:46.079 --> 00:34:48.550
appreciate it greatly. Uh, I think we're


00:34:48.560 --> 00:34:51.430
all done. Fred, thank you so much.


00:34:51.440 --> 00:34:53.270
Uh, a pleasure, Andrew. Great to hear


00:34:53.280 --> 00:34:55.270
from the listeners as always. Great


00:34:55.280 --> 00:34:58.470
questions. Uh, get my mind thinking


00:34:58.480 --> 00:35:01.349
again. [sighs] Uh, so uh, thank you


00:35:01.359 --> 00:35:03.589
everybody and thanks to you Andrew too


00:35:03.599 --> 00:35:06.790
for keeping on the rails.


00:35:06.800 --> 00:35:09.430
I do my best and sometimes I don't. Uh,


00:35:09.440 --> 00:35:11.349
but yes, thank you Fred. We'll see you


00:35:11.359 --> 00:35:13.190
next time. Professor Fred Watson,


00:35:13.200 --> 00:35:15.510
astronomer at large. And thanks to Hugh


00:35:15.520 --> 00:35:17.430
in the studio who definitely does keep


00:35:17.440 --> 00:35:18.790
it all together. Although he couldn't be


00:35:18.800 --> 00:35:21.030
with us today because um, he re-entered


00:35:21.040 --> 00:35:23.670
his garage at excess velocity. couldn't


00:35:23.680 --> 00:35:27.030
get down to subsonic speed and uh well


00:35:27.040 --> 00:35:28.790
he'll be in traction for a couple of


00:35:28.800 --> 00:35:30.630
weeks. Uh from me, Andrew Duckley,


00:35:30.640 --> 00:35:31.910
thanks for your company. We'll see you


00:35:31.920 --> 00:35:33.589
on the next episode of Space Nuts.


00:35:33.599 --> 00:35:34.470
Bye-bye.


00:35:34.480 --> 00:35:35.430
>> Space Nuts.


00:35:35.440 --> 00:35:37.510
>> You'll be listening to the Space Nuts


00:35:37.520 --> 00:35:39.750
podcast


00:35:39.760 --> 00:35:41.910
>> available at Apple [music] Podcasts,


00:35:41.920 --> 00:35:44.870
Spotify, iHeart Radio, or your favorite


00:35:44.880 --> 00:35:46.630
podcast player. You can also [music]


00:35:46.640 --> 00:35:49.589
stream on demand at byes.com. This has


00:35:49.599 --> 00:35:51.689
been another quality podcast production


00:35:51.699 --> 00:35:55.240
[music] from sites.com.