#418: From Cosmic Drag to Holographic Hype: Unraveling the Mysteries of Space Travel

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Hi there, thanks for joining us
on the Q and A edition of Space

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Nuts. My name is Andrew Dunkley, your host on this episode where you're

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going to be answering questions about light. It's an interesting question about how far

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away light has to travel before it's
undetectable. And he even gives you a

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measurement of how strong that light is, so we'll talk about that. Are

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we living in a holographic universe?
I think we've had that question in several

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forms over several years, so we
will tackle that one again. And how

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fast is fast enough to create drag
when traveling through space? And relative relative

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trouble with this word relativistic speed.
That's all coming up on this edition of

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Space Nuts Q and A fifteen second
channel ten nine ignition Space Nuts or three

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two space and I record it real
good and he's back again for more.

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Don't ask me why, Professor fred
what's an astronomer at large? Cello fred

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Illo, Andrew, It's good to
be back, whatever the reason is.

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Yes, indeed, everything good,
Yeah, all good. Well, it's

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all firing on two cylinders as usual, so that's yes, trouble as we're

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driving a V eight anyways, shall
we get on with it and go straight

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to our first question. This one
comes from Allan. Hi. This is

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Alan Scahill from Medicine Canada. My
question is if an led light one candle

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power in strength were to be turned
on in space, what would be the

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greatest distance a space tele telescope would
be able to detect it? Thank you

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and love your podcast. Thank you, Allen. Medicine Hat. Do you

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say medicine hat in Canada? If
that's an interesting name, I wonder why

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it's called that. He might have
to tell us. We might want to

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know what he's got a British accent
as well. That happens, I could

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ask the same about you. That's
a really good point. I never thought

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of that. Yes, medicine Hat. It's a city in southeast Alberta.

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It's located along the South Saskatchewan River. It's a problem in one hundred and

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sixty nine kilometers east of Lethbridge,
two hundred and ninety five kilometers southeast of

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Calgary. The city and the adjacent
town of Redcliffe to the northwest are within

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Cypress County. There is don't know
why it's called medicine Hat, though it's

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a great name. It might have
something to do with a nearby mountain,

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I suspect. Yeah, yeah,
it's the nearest we got to it during

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our expedition last month was to Calgary. We flew out of Calgary when we

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left Calgary a lovely place. The
bits I saw of it looked very nice.

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Yes, that's right, but it
was only the airport. Really we

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were. We were traveling down from
Lake Louise that day, and Lake Louise

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is stunning. So I can answer
for that. I think you've been I

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was wrong. It's got nothing to
do with a mountain. Apparently, it's

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derived from the Blackfoot Indian words samus, meaning the headdress of the medicine man.

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There you go, There you go. If I'm looking at the right

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place, I just did get quickly. I stand to be corrected. Alan

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so police. If I'm wrong,
let me know. Led light? Yeah,

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one one candlepower? How far out
before we can't see it? Or

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something to that. I've no idea. Look, it's it's it's all about.

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This is the interesting thing about light. It's yes, we regard it

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as a stream of photons, but
it's also a wave motion and light is

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something that basically has infinite travel possibility, and so that one the photons that

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that one candle power is emitting,
or the the light waves that the LEDs

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emitting essentially gone forever. But what
limits your ability to detect them is the

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equipment that you've got to do that. And you know if you've got and

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that's the key thing about telescopes.
The bigger your telescope, the bigger the

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light gathering area of your telescope,
the faint of the objects you can see,

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and therefore the further away you be
able to see your one candle power

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LED. I like, take it
on notice, Andrew, and see if

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I can do a calculation for that, because I do this sort of thing,

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or I used to when I was
thinking about star magnitudes and things like

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that. So one kind of power
LED and how far away could for example,

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the Hubble space telescope. See I
did have a quick look myself,

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and I I just found this on
the physicsforums dot com website and it says,

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and you said this earlier, there
is no known limit to how far

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light can travel. Yes, that's
right, but we're talking about the detectability

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of it indeed, and it depends
on the instrument. And I think Allen

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mentioned the hubble, Yeah, or
just a space telescope. Anyway, it

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doesn't matter that. We'll try and
do some calculations on that. Okay,

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Well that was easy, No,
it wasn't. Well it was easy in

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the sense that you know. The
answer is that light goes on forever.

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Basically, it's just whether you can
detect it or not. That's the tricky

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bit, that's the hard part.
Yeah, for sure. Okay, Alan,

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we'll get back to you shortly.
Now let's move on to our next

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question. This is a text question
that came in from Charles. What do

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you think of the theory that we
live in a holographic universe? Now we

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better qualify that by explaining what a
holographic universe actually is or is supposed to

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be. Let's just say that.
So, let's quote Leonard Suskind, who

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was one of the great proponents of
the holographic universe. The quote is the

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three dimensional world of ordinary experience,
the universe, filled with galaxies, stars,

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planets, houses, boulders, and
people, is a hologram, an

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image of reality coded on a distant
two dimensional surface. There you go.

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What's when does that date from that
quote? It's probably about twenty five years

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ago, because that's how long this
thinking has been going on about the holography.

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Actually that goes back only to two
thousand and eight, and it's from

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his book The Black Hole War,
My battle with Stephen Hawking to make the

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world safe for quantum mechanics. I
love the title. I've read that.

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So what you've got is the idea
and it comes from so think about what

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a hologram is. It is a
way of encoding lights. It's actually we

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would call it an interferogram in the
world of physics. You've got a film,

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in fact, a two dimensional surface
which is transparent, that has a

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pattern on it, which when you
illuminate it with what we call coherent light,

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that's light from a laser where all
the waves are in step, all

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the light waves are in step with
each other, then it will basically that

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light will be diffracted. It will
break up to form a three dimensional image.

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One of the best holograms I know
of is at Macquarie University in the

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physics department. I haven't honor appointment
there, so I go there quite a

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lot. And what they've got is
it's actually it's a conference room, just

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a small conference room with the table
and chairs in it. But one wall

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of it is lined with windows,
and on the other side of the windows

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is a corridor where you can walk, and that window. The windows have

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a hologround on them, and so
when you look through the hologround through the

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window at what is in fact just
a room full of chairs, what you

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see is a succession of images of
a bar as the night wears on,

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and the bottles are full to start
with, and everybody's everything's neat and tidy.

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By the time you get to the
other end of it, there's empty

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bottles all over the place. It
really not in good shape. So that

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is what we normally think of as
a hologram. It's something that gives us

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a three dimensional representation of a two
dimensional from a two dimensional So so this

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idea that the unit the universe is
like that I've always had trouble with because

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you know, a direct analog with
that with a hologram is that you illuminate

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it with something and the illumination forms
that three dimensional image. And so where

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does the illumination come from in the
you know, the holographic universe. So

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I think you've really got to look
at the details of this, and well,

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if I if I can read from
the Wikipedia entry on holographic principle,

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which is what it's all about.
The holographic principle is a property of string

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theories and a supposed property of quantum
gravity that states that the description of a

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volume of space can be thought of
as encoded on a lower dimensional boundary to

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the region, such as a lightli
like boundary like a gravitational horizon. There

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you go. So that's that's that's
what you're supposed to imagine with a holographic

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universe. So it's, as I
said, it goes back twenty five years,

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probably more than that. I've never
been that keen on it because it

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seems highly contrived to me, but
it does have a theoretical basis for people

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to think it might be the case. I'd like to see more evidence that

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there is, you know, there
is a holographic event horizon, if I

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can put it that way, because
I think that's the idea that the you

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know, if we're a black hole, the event horizon is actually where the

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hologram lies. And there's a whole
lot of gobbledygood on the Wikipedia page that

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if Charles wants to plow through he
might be even more illuminated on it than

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I. I find the theory very
confusing. It doesn't sort of gleane with

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traditional thinking, And no, it's
not intuitive. I find it hard argue

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against traditional thinking. Yes, I
understand that. I think by traditional thinking,

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I think you might mean something that
makes sense. Yes, the way

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we generally understand things the moment.
Yeah, traditional thinking. That's my perception

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of it. And who you are
really doesn't it. It's a thinking Yeah,

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well that's it. I mean,
we should be open to all possibilities,

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because the mystery of our existence at
all is one we can't answer.

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We don't know why it happened.
We don't know what caused it to happen.

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We don't know how things developed to
create what has been created. The

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more we look, the more questions
that are raised, the more we know,

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we get confused about things that shouldn't
have been able to happen, that

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happened, And it just goes on
and on and on. So you can't

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write off anything, I suppose No, and I wouldn't write off the holographic

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principle either. I think it's a
really interesting idea. I don't fully understand

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it as you've probably realized by now, I don't understand it that much,

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and that's so we So yeah,
So the answer to Charles's question is,

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yeah, I think it's it's interesting. As I said, I've never been

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a big fan. That's because I
perhaps I'm a traditional thinker, as you

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would put it. I'd like to
think about the universe as being made of

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atoms and things that really owe their
existence not to a hologram, but to

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to being where we are, to
being within a universe that was created in

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a big bang and has all these
other particles generated from that. That makes

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more sense to me. Now,
the next question that's going to come up

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is, hang on a minute,
what if the hologram is made of dark

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matter? Ah? Yes, I
think you've put your finger on something.

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Then you reckon probably just stirred the
pot even more and made it murky.

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But you know, the holographic universe
theory is fantastic in science fiction, really

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is. Yes. Yeah, I
am actually watching a TV series at the

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moment which I'm thoroughly enjoying. It's
called Dark Matter, and it centers around

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multiple universe theory. And I was
going to take a little bit of a

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break, but we might as well
throw straight into this. This is about

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a bloke who gets abducted and when
he wakes up, he's in a different

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universe and he's trying to figure out
what the hell happened because it's the world,

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but not as he knows it.
Same people, different situations, different

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relationships, different career path situations.
It's all out of whack and he thinks

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he's going mad. There's only been
three episodes so far, but g it's

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good. It is really good.
But the reason I bring it up and

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thanks for your question, Charles,
but this question popped into mind and I'm

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giving it to you without notice from
Rennie, who is a regular contributor.

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Could it be possible that our universe
is in a universe cluster as our Milky

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Way is in a galaxy cluster.
If all universes are expanding, would they

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eventually overlap each other at some point? I think the sort of standard multiverse

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idea is exactly that, that you've
got multiple universes which may be clustered together

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or not necessarily. One way of
looking at this is the M theory universe

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and M nobody's ever a short M
stands for mystery membrane is probably where it

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comes from, because the idea is
that we are all on a living in

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a three dimensional membrane which is right
next to other three dimensional membranes that contain

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other universes, and when membranes collide, you get a big bang. Yeah,

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that theory. I remember checking it
out once in quite some detail.

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And you know, we think of
these membranes as being well membranes with a

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universe somehow imprinted on it. But
it turned out in the theory it's actually

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when I think about it, it's
called the act pyotic theory of the origin

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of the universe, and it turns
out that these membranes are only separated by

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something like zero point five of a
millimeters. When nic collide, you get

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a big bang, and you're thinking, oh, that's a bit close.

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You know, something went wrong.
I'm not sure where m theory is at

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the moment in terms of its acceptance
by the cosmological community, but I think

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the answer terraneous question is yes,
that's possible. And if they keep expanding,

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which ours is, would they eventually
overlap at some point? I'm sure

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overlap would be I mean, what
if two universes that are expanding ump into

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each other. I think bump would
be an understate. Yeah, but they

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might be expanding in a higher dimensional
space, which might preclude that. Well,

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there's a thought too. And here's
another thought. If you've got two

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universes expanding towards it, towards each
other, and let's just say ours is

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one of them, Ours is expanding
at an accelerating rate. What if the

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one that's near us is expanding at
an accelerating rate, but their acceleration is

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faster than ours. Now, it
doesn't stand a reason that we're all going

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to hit at exactly the same speed. No, I think. I think

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you've got to ensure that your other
universe is in a different bit of the

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higher dimensional space than you are,
and then it can expand as much as

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it likes. And it doesn't doesn't
it ours unless it's a membrane. And

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that if it's a membrane and it
collides with us, you've got a big

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bang. Yeah, it's just like
watching child's balloons burst or rum or bubbles

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bubbles, they go boom. Yes, they could be mini universe versus that

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live for a fleeting moment and the
people go, oh, look at don

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it's all. It's really interesting to
talk about that. It's fascinating theory,

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and this dark matter series sort of
leans on that particular multiverse theory very very

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well, and they travel around in
a box just like Doctor whod Yeah.

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Thanks Rennie. This is Space Nuts
with Andrew Dunkley and Professor Fred Watson.

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Okay, we've tacked all space nuts. One more question, Fred, and

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this one comes from Craig. Professors. I'm Craig Miller calling from sunny Umbula

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in New South Wales. I have
a confession. I have a solitary habit

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n't usually mentioned in public. I
write science fiction, so that's this question

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is a little what if the vacuum
of space is, as we know,

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not exactly empty. The density is
low, but gas and dust fill the

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vac human space. So I'm wondering
how fast you would have to be traveling

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before that gas and dust began to
produce drag. Surely, if you went

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fast enough, you'd have to consider
aerodynamic principles for the profile of your spaceship.

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As a secondary question, wouldn't a
ship traveling at relativistic speed smash into

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that aforementioned gas and dust like a
mobile particle collider. If there were lots

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of spaceships traveling at light speed,
you'd see the trails all over the sky.

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Maybe. Anyway, thanks for answering
my question. Keep up with the

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great work. I love your show. Thanks very much, Chow, thank

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you very much. Craig, lovely
to hear from you. You'll have to

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send us some book titles. I'd
like to take a look at those,

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if you don't mind. I'd love
to see what your what your angle is

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and science fiction and steal your ideas. Now I'm kidding now my thoughts on

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his first question. You know,
how much speed to create the drag in

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the vacuum of space would be dependent
on the concentration of particles, would it

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not? Because some parts of space
only have one speck of stuff per gazillion

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miles. Now I'm exaggerating slightly.
Well, you're not exaggerating that much.

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Maybe the gazillion is a bit some
Yes, you're at the level of a

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handful of particles per cubic meter.
And it's a really interesting question actually,

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that Craig, that he poses because
even at those low densities, so we've

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got a sort of a bit of
an example of this around the Earth.

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When you get to heights of one
hundred, two hundred and three hundred kilometers,

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there's still enough of the atmosphere that
you're going to get drag on your

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spacecraft if it's in orbit, and
that's what brings them down. So here's

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the International Space Station four hundred kilometers
high that has to have its orbits boosted

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periodically every few months, I think, in order to counteract the effects of

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drag. And there's not that many
atoms of atmosphere up at that height.

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It's certainly well over one per cubic
meter. But yes, so the the

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atmosphere drag on a spacecraft is a
real thing, and I think to extrapolate

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that as Craig is doing, is
actually a valid thing to do. Should

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you think in aerodynamic terms, if
you were designing very, very high speed

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spacecraft, And I think the answer
is probably in the second part of Craig's

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question, because yes, those relativistic
velocities where you are approaching the speed of

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light, then your spacecraft is more
like a particle accelerator. It's more like

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what's going on at the Large Hadron
Collider where you might well see you know,

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atomic scale impacts that would have showers
of other particles coming off them.

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So you know, your occupants of
your spacecraft might be being irradiated by highly

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ionizing radiation from the particle impacts that
you're traveling through, which would be not

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very nice. If you've got dangerous
rays coming out of the walls of your

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spacecraft, no matter how aerodynamic it
is, you're not going to be very

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happy about it. So I don't
know that specific answers to the questions,

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but it's really it's a really interesting
one. You know, I can't tell

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you what velocity you really need to
think about designing. And you're absolutely right

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as well, Andrew in that different
bits of space have got different densities.

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If you're looking at the star formation
region, a nebula, as we would

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see it as the pressure there is
unbelievably low. It's lower than the hardest

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vacuum you can make on the Earth, but there are still enough particles there

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that you're essentially forming an EBuLa.
You're seeing the glow of it, Whereas

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in regions between the galaxies the density
of particles is very low, indeed,

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but it's still there. They're still
there. The particles subatomic particles are still

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there. So yeah, if you
were capable of traveling at the light speed

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and you wanted to travel any significant
distance, you'd have to really be able

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to calculate your navigation with so many
parameters in play. It's not just about

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I want to go from there to
there, because there won't be there you

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get there, it'll be there somewhere, and you've got to allow for what's

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in between to make the trip without
sort of hitting something, you know,

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like a giant star or whatever.
It's it's it's uh. I think interstellar

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navigation would be a very tricky little
thing, tricky chop. Well, we've

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got spacecraft that are doing that,
you know, basically with with the Voyagers

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and the Pioneers there in effectively interstellar
space. They're still they're still feeling,

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all of them, but some of
them are feeling the magnetic field of the

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Sun rather than the magnetic field of
the galaxy. I think Voyager one feels

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the magnetic field of the galaxy.
So yeah, you're out there in in

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very deep space. I wonder whether
you know we certainly. I'm just trying

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to think of this the other way
around. Particles what they do. When

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I was building instruments for ground based
astronomy. Back in the eighties, nineties,

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early two thousands, we were often
beset by the effect of cosmic rays,

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which are seatomic particles coming in at
a very high speed on our detectors.

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You'd get you get an image that
was supposed to be the spectrum of

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an object, but it have all
these It looks as if somebody had thrown

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a whole lot of just white bits
of sand all over the image, and

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they were the impacts of cosmic rays
which were being recorded by the detector.

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Wow. So that sort of thing
must happen when you've got a spacecraft,

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you know that's doing science or imaging
or whatever. You must have this cosmic

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ray flocks anyway. But if you've
got a significant velocity in a particular direction

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that might affect the cosmic ray flocks, you might see more than more than

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you expected or less than you expected. Yeah, it's a really interesting thought.

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Thank you for bending our minds in
that direction, Craig. Indeed,

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yes, and I mean it when
I say send it. Send me some

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intro about your sci fi books.
I'd love just see what you write about

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and if you do have questions for
us, of course, please send them

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through our website, spacenuts podcast dot
com or spacenuts dot io. You can

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click on the AMA link at the
top and send us text and audio questions,

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or the little purple button on the
right hand side to send audio questions

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only. But as we always say, please remember to tell us who you

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are and where you're from. You
might be from medicine hat in Canada,

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who knows. And thanks to everyone
who contributed, Alan, Charles, Rennie

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and Craig. Looking forward to some
new questions in coming weeks. And that

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wraps it up for another episode.
Fred, thank you very much, Oh

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thank you. Thanks for having me
and thanks for everybody's questions. Is very

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stimulating, it is, isn't It
gets a brain going sometimes he does.

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Yeah, people dooms a lot.
Yeah. Thanks Fred. We'll see you

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soon and see your light to cheers
for the bye. Fred Watson, astronomer

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at large and here in the studio. Who does what? Who does in

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the studio? When he's not in
the studio, I don't know what he

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does? And from me Andrew Duncley, thanks for your company. See on

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the next episode of space Nuts coming
to you real soon. Oh Bynuts to

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The Space Nuts podcast available at Apple
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