Fusion Rockets, Ditching Heat Shields, Looking Beyond the Edge of the Universe | Q&A 176

[@WilhelmDrake]

Dear Mr. Cain, You sir, are a good person. I wish you all the best. We need more people like you.

[@frasercain]

Thanks!

[@thedevereauxbunch]

First Q&A was fantastic. Thank you.

[@isaacplaysbass8568]

Another awesome Fraser Cain Q&A; thank you :)

[@frasercain]

Thanks!

[@Swede_4_DragonBeliever]

A big THANK YOU from Sweden! I love the longer formats. 40+ minutes is gold! Question. Don't BH's loose mass when they merge in the form of energy/gravwaves?

[@charleslivingston2256]

Correction: JWST optics are fixed relative to the sunshield. Everything rotates together. From the "neutral" position with the sunshield perpendicular to the Sun's rays, it can yaw 360°, pitch up 45° or down 5°, and roll +/- 5°. This band covers 39% of the celestial sphere. As this band rotates about the Sun, over 6 months the entire celestial sphere is in coverage. JWST can't see within 45° of opposition. Because of this, points on the ecliptic have the fewest days in coverage (101). There is a little over 50 days "looking forward," a little more than 90-day gap, and then another ~50 days "looking back."

[@saumyacow4435]

Regarding that propulsive landing idea. Whilst its impractical for re-entering Earth, Mars is a different story because Mars requires far less delta-v. (About 4 km/s for Mars versus 9.5 km/s for Earth). As a consequence you don't need a heat shielded vehicle to deliver people from Mars orbit to Mars surface. In fact (with refuelling) you now have a fully reusable lander and ascent vehicle. It surprises me how much resistance there is to the whole idea of a fully propulsive lander for Mars. The orthodoxy has it that it must have a heat shield. But a fully propulsive lander has several advantages. I'll list them - Far lower g forces on re-entry (around 1.5 Earth gs versus 5 or 6 for what is currently proposed). That's a huge win for people exposed to zero or low g for long periods in space. - Entry without the plasma sheath, so that you have constant comms/navigation all the way down, meaning a better chance of a more accurate landing. - Less sensitivity to Martian weather (air density fluctuations and wind) which again gives you a better chance of a more accurate landing. - The ability to do surface to surface hops and being able to land anywhere on Mars (conventional aerodynamic landers are restricted to below Mars "sea level" which excludes half the planet. - The ability to be used in orbit for orbital transfers or excursions to Phobos.

[@PereBouSabria]

If lasers are the only practical way to achieve interstellar travel, perhaps our only chance at travelling to another star and then slow down at destination rather than fly by at incredible speeds is to first detect an advanced civilization, make contact, exchange plans for building similar laser stations in both solar systems and only then start to send spacecraft. Sounds like a good science fiction idea to me!

[@joshderoos]

Hey Fraser! I watch a lot of astronomy content, including yours, but one area that doesn’t seem to be talked about is the coordinate system that is used to locate known objects in the universe. It must be complex considering that the earth is rotating and orbiting the sun, so everything we observe is also moving relative to us. Can you give us a Cliffs Notes explanation?

[@frasercain]

Astronomers use a designation called Right Ascension/Declination, essentially two numbers that define the height above the horizon and the distance away from the March equinox. Essentially space latitude and longitude.

[@johnbennett1465]

@@frasercain that explains how you point a telescope at an object. How do they record the positions of objects such that you can figure out where to point at any time? I know they make full 3D maps of positions and velocities. This requires at least 6 numbers per object.

[@billyhomeyer7414]

@@johnbennett1465 can you explain how a light bulb works and how it gets its energy? “Oh yes, you turn the light switch to the on position.” Gee thanks now I know everything. Lol, watch the movie stargate

[@johnbennett1465]

@@billyhomeyer7414 what does your question have to do with my comment? I went to CALTECH and have a solid science background, but I would never claim to have the depth of knowledge that a scientist has about their subject area.

[@billyhomeyer7414]

@@johnbennett1465 my sarcasm was to reflect your question not being answered (two dimensions vs the three you asked for)

[@thebigerns]

Hey Fraser, I really enjoyed this episode. My question to you… since the objects we see that are further away from us are also seen further back in time, doesn't that mean the acceleration we observe with distance is also in the past… and that the universe nearest us in space and time is actually decelerating? (Yes, I'm being serious, and always thankful for your thoughts)

[@LeopoldoGhielmetti]

They measure the recession speed of galaxies. If they were faster in the past, it means the universe is decelerating (i.e. acceleration is negative), if they measure that the speed was slower in the past, it means the universe is accelerating (i.e. acceleration is positive). The speed measurement is done looking at the Doppler effect on the light. I don't think that this effect is influenced by the distance in the past (except by the expansion of the universe itself that is what they are measuring or the gravitational field of the Milky Way itself) and I'm pretty sure that all those influences on the Doppler effect measurements are already taken in account by the astronomers.

[@thebigerns]

@@LeopoldoGhielmetti Okay, so REDSHIFT or "doppler" is supposed to be a way of measuring how "stretched" out the light from these galaxies is… how much the space between us and them has expanded to account for that shift. My point is we always try to understand this process in terms of distance but not in time… the redshifted light from more distant galaxies is much OLDER than the less redshifted nearer ones, but we use distance to infer acceleration when the axis of TIME suggests something else. That's all I'm saying with my question, which I think is fair. Thanks for your reply.

[@absalomdraconis]

@@thebigerns : Our local region of the universe is arguably shrinking (by virtual of the approach of Andromeda and Triangulum, and perhaps because of our galaxy's dark matter), but we _don't know_ if that should be considered a strictly local (and presumably temporary) anomaly, or if it instead is indicative of the "current era" of the universe. This is one of those things that would tell us a lot more about dark energy and dark matter... but which we just don't know the answer to.

[@Pidxr]

L Krauss once said in a talk that a big crunch was avoided earlier when the expansion energy started to outpace the contraction of gravity. But should we see a bend in the expansion curve at a given redshift, and should this be named the Krauss Redshift?

[@friendlyone2706]

Thank you for your generous time donation to us information junkies.

[@AvyScottandFlower]

I like your attitude towards advertising I try to always watch UT's videos and shows from my phone (not my work PC) so the ads play, and I can contribute to the show.

[@garyswift9347]

Question: Should mission planning, such as a decadal survey, be taking starship into account yet, or is it too early? If it's gonna work, then they need to be planning now, no?

[@magistratp2]

You described the price of creating anti-matter. So.. antimatter can be created? What has been done with that so far? What's the state of the research? Thanks a bunch! Keep up the good work.

[@esquilax5563]

They can make a few particles at a time at accelerators like the LHC. Storage is a problem

[@frasercain]

Many hospitals have a way to create antimatter for their PET scans. Look up the tech for how they work.

[@boredgrass]

"...a black hole is a smushed star." I like that!🤗

[@rgraph]

Thanks for answering my question! :-)

[@asapautosolutions]

Traveling across the Atlantic was life threatening and very difficult. Traveling west and settling North America was life threatening and very difficult. I think we will look back on this moment in time and just think that colonizing our solar system was a "no-brainer" and necessary.

[@charleslivingston2256]

When black holes merge, a tremendous amount of energy is radiated away as gravitational waves, so the mass of the resultant black holes is smaller than the sum of the two masses.

[@davecarsley8773]

Nope. Any mass that was in either of the black holes stays in those black holes when they merge. NOTHING escapes a black hole once it's in. Neither light, nor matter, nor mass.

[@jamesdubben3687]

Pause exactly at 22:30, Fraser, when he gets a question that is exquisite.

[@cypercharged]

Thanks for your answer Fraser. We always see images of JWST with its mirror facing parallel to the heat shield, I didn’t know that it could move without moving the whole shield

[@johnbennett1465]

While it is hard to find a clear answer on the web, I am pretty sure that the mirror does not move relative to the sun shield. Fraser's answer is half correct. The rotation of the Earth around the Sun does allow JWST to see in all directions over the course of a year. I don't think it can point directly away from the Earth. Instead it can see a circular swath sideways.

[@MrT------5743]

The JWST cant change the primary mirror in relation to the sun shield. It moves the whole thing mirror and sun shield together. At any given time it can see about 39% of the whole sky. It cannot see directly away from the Sun/Earth direction at all. But over the course of 6 months It can see the whole sky. Scott Manly has a great video on this. kzbin.info/www/bejne/maHCaHSAqMqMj8U Look about 7 minutes 31 second for how much it can pivot.

[@cypercharged]

@@MrT------5743 very interesting, thanks for the link :) So indeed as I initially thought the field of view at a certain moment in time is quite constrained

[@explosiveapple1]

Hey Fraser, what created the gravitational waves that formed the first stars when the universe was nothing but gas? Or were there regions of higher and lower densities of gas that formed the stars that then made more stars. Thanks

[@j7ndominica051]

I believe the questioner asked about the range that the receiving dish can tilt across or gimble, if at all. On pictures we only see the Webb Space Telescope pointing "forward". It can't see the space "above" it. Fictional space ships rise up from the ground through magic. They only flames coming from one end to push the ship sideways.

[@deantoth]

long time listener. At 3:23 , Fraser, i believe you are misunderstanding the question. There is research that looks at galaxy clusters at the edge of our observational limits and can infer galactic mass structures beyond our light horizon by their gravitational influence on objects on this side of the horizon. and yes this does take into account that the events being seen are 10 billion years old. ( or whatever the current light horizon limit is, i don't exactly recall) as a nearby example, consider the great attractor. imagine if the middle of our own supercluster was the light horizon of a distant observer. they would see the effects of the great attractor even if it was on the far side of the horizon for them. just imagine an equivalent event happening 10 billion years ago that we are just now looking at. sorry for the caps, for some reason my voice dictation is not capitalizing sentences.

[@zerrozg]

Hey Fraser, great show as always. I have a question. Do you think we will see a third New Horizons fly by of an object deep in the Kuiper belt? If not, what can the spacecraft teach us science wise in years to come? Thnx

[@frasercain]

In theory New Horizons could reach one final Kuiper Belt Object. They're searching for it now.

[@zerrozg]

@@frasercain thnx. Any chance for getting Alan Stern for an interview soon? :)

[@SirLothian]

In your message today, you said that every minute, we see one light minute further back in the CMB, however I suspect we see a lot less than that. The wavelength of the light from the CMB is very red shifted, so I would think that the expansion of the universe makes it so we see only a small portion of a light minute further into the CMB for every minute we observe.

[@davecarsley8773]

just because light is redshifted doesn't mean it's "less light". It's just a different length of wave.

[@bryandraughn9830]

Something else that is often overlooked is that the objects that are currently near the edge of our visible horizon, have no problem seeing beyond it because their visible horizon extends beyond it.😊

[@ericgolightly8450]

Everybody has their own visible sphere.

[@roccov3614]

0:22 "... could they just slow down while they're in space and drop into the atmosphere ..." Yes. Just like SpaceX does with their Falcon 9 first stage. If they didn't do a re-entry burn they would most likely burn up. Surprised Fraser didn't mention that.

[@MrT------5743]

The first stage is not going fast enough to burn up. Otherwise they would burn up during launch.

[@roccov3614]

@@MrT------5743 Maybe they are not going fast enough to completely burn up but they do need to do a re-entry burn or else risk damage to the rocket. I don't know why you brought up launching but they do throttle down during max-q to avoid damage as well. That's sort of similar.

[@MrT------5743]

@@roccov3614 there entry burn is so they go back in he direction they came from to land back at the launch pad. The first stage is not going fast enough to go into an orbit, so they would reenter either way, just don't want to reenter half a globe away.

[@roccov3614]

@@MrT------5743 You're a bit confused there. If they want to go back to where they came from they do 3 burns; a boost back burn, a re-entry burn and a landing. If they land on a barge they just do the re-entry burn and landing. It sounds like you haven't seen many launches.

[@MrT------5743]

@@roccov3614 It seems you do not understand why there is a second stage. To get the Crew/Cargo Dragon into orbit. So therefore the first stage is not going at orbital velocities so a "reentry burn" is not needed since it will re-enter either way. I did confirm this and looked at a Falcon 9 Mission profile just incase I was wrong. You were right about the 3 burns, well sort of. The first burn is not a burn per say but is just thrusters to flip so bottom end is facing in the direction it is going to prepare for re-entry. Second burn slows the descent for landing and aims for the landing site. The third burn is for controlled landing. None of these burns are called a re-entry burn.

[@shockslice7632]

So, what I gather about the hubble sphere question, is that we can still see the whole universe (discounting the earliest opaque state). How long then till the oldest & furthest stars slip beyond our view, as if they never existed?

[@frasercain]

About 100 billion years from now.

[@dominic.h.3363]

10:30 - maybe just accelerate a craft that has a propulsion engine and enough fuel to do a gravity assisted deceleration maneuver around the target system's sun? The photon pressure should also help. It would still be a one-way trip (unless it's feasible to lug around parts of a second laser that could be installed remotely), but sending some probe this way that at the very least can gather telemetry should still be of great scientific value. Of course only for a civilization of people who don't mind waiting a decade plus for results... and if JWST is any indication, we really don't.

[@jondoc7525]

Elons our last hope cracking the corrupt whip exposing it

[@bbbenj]

Thanks 👍

[@ocoro174]

finally, more fraser 😍

[@jlmwatchman]

Fraser Cain answers a few questions that I have commented about; Future Rocket Fuel to help us reach the stars that are impossible until a new fuel or mater is created or stabilized like Anti Mater. Nuclear Thermal Propulsion is just powerful enough to explore our solar system… The second or third thing we should do with the new Nuclear Tugs is to use them to find and mine the Negative Protons that I’m sure we will find closer than Jupiter’s Orbit? Once we stabilize the abundance of Negatives Protons of our solar system that are also known as Anti Mater, we will be getting to Mars faster even though we will be going to mars the long way, just real fast… There was a question about the Earth’s L-Points that I learned aren’t as stable as I once thought. Fraser tells us that we will need fuel to stay in place, as in the new James Webb Telescope is moving in a circle to stay at the L2-Point. en.wikipedia.org/wiki/James_Webb_Space_Telescope I’m guessing that the space rings I commented about will need less fuel to stay at the L-Points of Earth. Since people are saying that the surface of Mars is more hostel than onboard an Orbiting Habitat, Elon Musk should have plans for Starship Habitats. I’ve commented about four Starships connected at the nose, spinning at the Earth’s L-Point 1 in-between earth and the moon to protect the habitants from excess solar radiation. en.wikipedia.org/wiki/Lagrange_point_colonization Fraser Cain answered other questions, I just wanted to point out the, ‘three most interesting questions that were asked by someone who read my comments?’ You can find my comments at; thenewmars.wordpress.com/ and everywhere people have shared them??? LET’S GET THERE ALREADY!

[@Monsmak]

What was estimated size of the universe when the light from the cosmic microwave background was generated?

[@ericgolightly8450]

The observable universe is 93 billion light years across today. If I remember correctly, that sphere would have been about 88 million light years across during CMB.

[@bryanhager5403]

The other problem with Ram jets is that when you collect the interstellar protons the inertia of their mass will slow the ship. The result is, even with unlimited energy, you cannot go faster than your exhaust velocity. The faster you go the more the inertia of the scooped protons will slow the ship.

[@smenor]

When I was watching The Expanse I did the specific impulse calculations and it was super disappointing to see how short of a trip we would be limited to at 1g acceleration even if we had an almost impossibly good fusion drive

[@Scipio-Africannabis]

Do you mean 1g? I'd have thought at 1g you'd be able to get as far as you got until you died of old age...

[@frasercain]

You could accelerate at 1G forever if you wanted to, you'd just experience more and more time dilation until billions of years of time were going by for every year you experience. Trips in the Solar System would be measured in days and weeks at the most. That's not too bad.

[@smenor]

@@Scipio-Africannabis yeah for realistic fusion rockets the specific impulse is only in the range of tens to low hundreds of thousands of seconds ( order of days at most ) so while it's way better than chemical rockets, it ends up working out to be a shockingly short time at 1g or any significant fraction

[@smenor]

@@frasercain you could do that within special relativity, but not with fusion :)

[@cacogenicist]

@@frasercain - Regarding geothermal (arethermal?) energy on Mars, see the Cerberus Fossae region. There are ongoing magma intrusion Mars quakes, and evidence of relatively recent volcanism. So, maybe we could tap the heat in that area, at some point.

[@neptunethemystic]

Hey Fraser, really miss the documentary videos. How comes you dont make them anymore any chance you will again?

[@mralekito]

I know Fraser knows this - you couldn’t see any satellites from 100 light years away because you would be seeing earth as it was 100 years ago - and there were no satellites then.

[@frasercain]

Hah, good point.

[@Wildblood]

If a planet's orbital distance from a star is determined by its speed, then how can it migrate in/out? If Jupiter started out in the inner solar system, did it need to accelerate in order to reach its current distance? If so, where did the force to accelerate that insane mass come from?

[@jmacd8817]

Interactions with other planets perturb caused Jupiter’s orbit to move. Obviously, Jupiter has a much bigger effect on the other planets, but Jupiter is affected as well.

[@Wildblood]

@@jmacd8817 Considering Jupiter's mass is 2.5x all the other planets combined, did they really have enough mass to cause it to migrate so far? Did it gobble smaller planets up as it moved out and if so, would this explain where the force came from (i.e. Jupiter being smaller and easier to perturb, whilst the solar system had more mass to move it, until it got eaten up as Jupiter migrated).

[@disinclinedto-state9485]

"livin' this trailer lifestyle..."

[@frasercain]

One month to go...

[@Paul_Ch52]

38:30 What? We see short gamma ray bursts all over the cosmos. Yes, lots of competing explanations, which include primordial black holes evaporating.

[@frasercain]

Those are mostly explained by supernovae and other events.

[@dustman96]

I'd say This Guy's question does make sense if the big bang was an isolated incident in a much larger(or infinite) universe. I believe he's asking if the perturbations of the stuff we can see would be evidence of massive objects or clusters of objects well beyond what we believe to be the edge of the universe as created by the big bang. Fraser is maybe saying that we wouldn't be able to see through the haze of the early big bang part of the universe?

[@frasercain]

No, I got the impression he was imagining the Universe as a giant sphere that we can see, surrounded by stuff that we can't see. And the stuff we can't see is pulling with its gravity.

[@robertjundi5934]

Do an interview with Stephanie Thomas from Prinston Satellite Systems on their linear fusion drive

[@ronaldgarrison8478]

You can't directly compare the fuel and rocket size required to re-enter, without a heat shield, to what you would need to go into orbit. Going into orbit, you want to get up as fast as you can, to expend less fuel fighting gravity. Coming back, you want a shallow angle, to bleed off speed before you get to thicker atmosphere. You don't need to come to a dead stop to eliminate the need for a heat shield. Getting down to maybe 20% of orbital velocity might be enough. You might want to land vertically for other reasons, but that's another matter. There is one thing to be very careful about, though: If you start a strongly powered re-entry without a heat shield, you MUST complete the burn, or you will burn up. Either that, or you need to very promptly burn more fuel to get back into orbit. If your rocket fails partway through, you are in big trouble.

[@elck3]

Hi Fraser, is there physical matter behind the event horizon of a black hole?

[@edwardgalliano9247]

The answer is obvious. We are in Euclidean space inside an elliptic plane. It's just light is red-shifted by elliptic gravity.

[@alflud]

It seems that every little patch of sky we do a 'deep field' on reveals a plethora of galaxies all over and this implies that _no part of the sky_ is actually empty, that wherever we look, if we look long enough we'll see that there are galaxies literally everywhere, right? My question is this, if there are galaxies filling up every 'dark' patch of sky then how can we see past all those galaxies to the background (CMB) of the universe? If the galaxies weren't emitting then we couldn't see them but since they are emitting then how is it that we can see past these emissions to the background that's behind? Is the CMB just passing through all of these galaxies basically untouched?

[@virutech32]

The CMB is everywhere. It's not past the galaxies or coming from outside the observable cosmos. The entire cosmos was filled with photons at the time of last scattering. they were everywhere including between galaxies & stars & such so they don't have to pass through everything though galaxies are mostly empty space so they largely would anyways.

[@frasercain]

Essentially yes, the photons from the CMB are passing through galaxies. They're only really impacted when there's a region with a lot of dust. But when you think of a galaxy, it's made of stars. And stars are essentially points of light surrounded by light-years of empty space.

[@citinerve]

Hi,when we can expect nuclear fusion rocket or space ship to travel one galaxy to another.

[@kennethhicks2113]

Premortal blacks holes may be responsible for the lack of antimatter in the early universe too.

[@frasercain]

Hmm, interesting. I hadn't heard that, but it makes sense.

[@oldmandoinghighkicksonlyin1368]

*Primordial

[@kennethhicks2113]

@@oldmandoinghighkicksonlyin1368 Ty... old fingers and mind don't work like they used to! Wait... it was auto-incorrect! lol... Have a good one sir.

[@CyberiusT]

Question: Given that the LeGrange points are gravitational regions of balance interaction between Sun and Earth, shouldn't there also be analogous 'points' of between Earth and Moon - even if tiny and less stable?

[@frasercain]

Yes, there are 5 Earth-Moon Lagrange points. L4 and L5 will be perfect for putting giant orbital space stations.

[@CyberiusT]

@@frasercain Ah, my misunderstanding - I thought Ls 4 & 5 were other Earth/Sun interactions.

[@robertsutton8894]

Could have done with consideration of how long last is in question 3

[@explosiveapple1]

What if you used a really big mirror at the destination to slow the craft down instead of another laser array

[@virutech32]

You would still have to build the mirror at the destination & a stellaser is just a pair of mirrors so for interstellar travel there's no real difference. Also cuz of beam divergence you'll have to make the return mirror way bigger than your sail. You have to worry about kickback on the mirrors themselves too. They'll get the same kind of push ur sail does so orbital management for them is more intensive. Otherwise it is probably doable

[@HPA97]

If planet 9 is a primordial black hole. Wouldn't it be almost impossible to detect it due to having incredible small event horizon?

[@ericgolightly8450]

He talked about that in another Q&A

[@PaulBrunt]

Are you sure we could use a laser light sail for interstellar travel? Laser beams diverge, it might be small but it adds up. If you assume a divergence of 1mrad or ~200archseconds, a sail with a diameter of 1000m would appear as

[@absalomdraconis]

Yes, we're certain. The thing your forgetting is that the size of the _focusing element_ also plays a role- the larger the focusing element (perpendicular to the path of the beam), the further that the beam will maintain some intensity of light. I forget the name, but there's a famous sci-fi book that was written by someone that did the math for a trip to Barnard's Star (that version _also_ included a life-elongation drug). Regardless, the trick to doing it is currently to find a way to obtain thrust from an external source. No thrust generated by the vehicle will be useful for interstellar voyages with foreseeable technologies, because the power/thrust system will just weigh down the vehicle too much.

[@NullHand]

I think the laser light sail idea is to accelerate your probe early in it's flight path, like still within our solar system. Slowing down is right out currently. Since all the expense is building the laser, its power supplies, and focusing elements, it would make sense to me to send a chain of probes, communicating backward through the chain. Each one will hurtle through the system with not much time to observe, but may be able to inform incoming probes what objects to focus observations on. All data would be passed back to Earth would arrive 4± years after the probe chain did its thing.

[@Muhahahahaz]

Eccentricity has nothing to do with why JWST moves around. L2 is an unstable Lagrange point. Even if Earth’s orbit were perfectly circular, it would still have to orbit L2 and use propulsion to stay in place

[@echofloripa]

How far can two objects be in L2? Minimum and maximum.

[@17ephp]

Q&A What is required to produce antimatter, physically? Its not money, its labor, machinery, and compounds. So what it's needed and why it's so "expensive"?

[@frasercain]

You need electricity to run a particle accelerator that smashes the atoms together, and then more electricity to run a magnetic confinement to hold the antimatter away from all other matter.

[@richardgould-blueraven]

Wait a minute, if light moved instantaneously wouldn’t every part of the night sky have a light source? No black in the night sky?

[@dax9943]

Fraser, another great video. I have been thinking about the expanding universe and don't understand something. I know based on Hubble's work and subsequent verifications the farther something is from us the faster it appears to be traveling away. What I don't understand is the farther it is then also the further back in time the object also is. If the ancient object emitted light earlier than something closer then how can dark energy red shift it more than something closer even though the closer object had more time to be acted on by dark energy acceleration?

[@fep_ptcp883]

If the object is farther away, its light was emmited longer ago than the light of a closer object (assuming we're able to see both objects simultaneously). If its light was emmited longer ago and is since then travelling towards us, there was more time for dark energy to stretch it, shifting it to the red end of the spectrum. Think of dark energy as an escalator going down and photons are kids going up against it. The farther down the kid starts walking up, the more tired he will be when he reaches you at the top (in comparison to how tired he would be if the escalator was stopped). If both kids arrive at the top at the same time and walk at the same speed, it is true the kid who started farther down must have started walking earlier and for sure will be more tired (redshifted) than the kid who started climbing up from the middle of the escalator.

[@dax9943]

@@fep_ptcp883 That's how I originally thought of it too, but we are always given the example of the train passing as an example of red shift and blue shift. If that example holds water the effect of the red shift and blue shift is due to the movement of the train when it emits the sound, as it emits the sound. Said differently the shift in spectrum occurs at the moment of emission not while the packet of energy is traveling. A single photon packet would have to travel a longer distance in expanding space why would that change the wavelength?

[@fep_ptcp883]

@@dax9943 both cases (the moving source or space stretching due to dark energy) have to do with the fact that the speed of light is finite. As I understand, the incoming speed of the source does not add to the speed of the light, instead adds to its energy (blueshift) and the opposite happens to sources that are going away from us (the movement of the source does not subtract from the speed of the light, it only makes it less energetic, going reddish). If space stretches, it does not make the light go slower, but makes it lose energy along the way (it gets "more tired" on the way towards us). This is how I wrap my head around this subject, but I'm not a professional

[@dustman96]

It's interesting to me that we don't consider that our observations could be wrong, our science could be wrong, etc, when it comes to the expansion of the universe. I believe the universe is still in the process of exploding and will eventually start slowing down. That, or there is more mass outside what we can observe pulling our part of the universe apart.

[@dylangreen6075]

Or, it's been slowing down all along. Things farther away appear to be accelerating away from us because they were when that light left. Surely by now it's slowing down, we just can't see it yet.

[@frasercain]

Scientists always assume their observations are wrong. They try everything they can to disprove their theories. Only the ones that last have a chance of maybe being right.

[@psycronizer]

I have to disagree with Fraser's take on Lasers to propel a craft rather than fusion. Lasers can theoretically propel to some percentage of c over time, but the thrust would be minimal because of the massless aspect of the photon. But a fusion drive can also do the same, the fusion process itself is relativistic AND there is of course significant mass associated with fusion . One of the bigger problems with using fusion, apart from the obvious ones, is leveraging that energy into a useable form of propellant, essentially taming it down enough so as to funnel and shape it to the equivalent of a De Laval nozzle, so as not to be basically become a giant bomb. The only thing capable of doing that is electromagnetic fields, similar to a Tokamak. Essentially, it would be magnetic bottle, the obvious advantage over any ground based laser system would be a propulsion system that is controllable, from zero specific impulse to some absurd number only limited by the technology applied to dealing with other absurd problems, like running into a grain of sand at some lower percentage of c, which might prove catastrophic, even though the void between solar systems is almost completely empty, it's totally empty, and it might ruin your day ! but for travel inside a solar system, a fusion based propulsion system would be essential for human convenience etc.

[@JohnSmith-kf1fc]

Great video:) here is a question: would i feel an atom of iron hitting my hand at the speed of light?

[@Theoverthinker81]

No! Because it's impossible for matter to travel at the speed of light. However at 99% the speed of light it would roughly feel like a fly landing on your hand.

[@JohnSmith-kf1fc]

@@Theoverthinker81 thats a rather pedantic answer but ill take it :)

[@cartermclaughlin2908]

I thought air atoms each travel pretty fast, and we experience their average speed as temperature. One atom of any element would not be observable. Our sense of touch does not have that sort of resolution. I imagine at (ok, NEAR) the speed c, it world pass right through you, or worst case, be more like radiation if it actually collided with your meleculea. I give shots as a nurse and if you give a good flick of the wrist to get through people's sensitive skin quick, they don't even feel a small needle - say 24g or smaller.

[@MrT------5743]

@@Theoverthinker81 You say no cause matter can't travel the speed of light. But then give an answer for 99% the speed of light not taking into account humans need to breath air and can't live in a vacuum so their would be at least air or a pressure suit the iron would have to also travel through. See two can play this game.

[@Theoverthinker81]

I wasn't being pedantic, funny etc as their are so many variables. I asked myself a similar question: what would you feel if you stood in front of the Large Hadron Collider firing one beam? Research suggested the energy value would be 10-13 teraelectronvolts on coalition. The iron atom might collide with air particle(s) splitting them causing a small fission chain reaction and hitting you with just gamma rays (pedantic). It may just dissipate as heat depending on range and so on. It's a greet geeks paradise of a question I think :0).

[@richardchan1498]

First time commenter question: If the gravity of a black hole is so great that it absorbs light, then could it theoretically also function as a worm hole accelerating light through it to a white hole on the other side?

[@virutech32]

It doesn't really absorb light so much as it's escape velocity is higher than light speed. Some have speculated that some kinds of black holes might function as one-way wormholes, but it is basically pure speculation. We have no way of knowing though since, being one-way, there's no way to get data back from the other side

[@MrT------5743]

If a black hole sent anything 'out of the other side' then the black hole would not exist. It exists due to the mass it contains. If that mass were lost somewhere else, it wouldn't be a black hole anymore.

[@MrCoxmic]

we need a permanent colony on the moon, long before thinking about mars

[@jondoc7525]

Eh much with turnaround team both are accomplishable if it was the actual goal . Work in colony as we visit . . We could sent supplies to mars right now heh

[@derivious2012]

so fraser, planning on visiting australia again?

[@frasercain]

I'd love to. But really, I'd love to go anywhere. I haven't even eaten at a restaurant since the pandemic started.

[@stephengordon4081]

Could neibering universes be pulling ours apart?

[@citinerve]

Basically we are talking about time machine,

[@HotchkissJoe]

I have to take issue with your description of the Lagrange points. L1 L2, and L3 are "meta-stable" i.e stable if not disturbed from the precise Lagrange point. L4 and L5 are actually "stable". "meta-unstable" makes no sense.

[@frasercain]

Hmm, I'll double-check and make sure I'm using the correct terminology. Thanks! But the key is that the Lagrange points aren't a point. They're blogs that change in shape as the Earth goes around the Sun.

[@Jefff72]

Could there have been other Big Bangs? If our Universe is 13ly across, could there be a neighbor Universe say 20ly from us? I don't mean parallel universes. Since ours is expanding faster and faster, could it expand into another Universe?

[@larsalfredhenrikstahlin8012]

it's not 20 ly, it's roughly 90 billion ly- 13.8 billion years has passed but the universe has expanded as well that's why it's abt 90bly.

[@brien9648]

It seems contradictory in my mind to say the universe is infinite while as the same time to postulate at some point it was very small (e.g. size of an atom, or volleyball) . How can something go from having a defined "size" to being without end? Also, when considering how the universe itself cooled down, was that energy radiated into itself? Or into possibly into whatever is outside our cosmological horizon? Both seem to point (at least in my mind) that there is a defined size to our universes.

[@MrT------5743]

I do not know how they know the universe was infinite density in an infinitely small point but I do know, no one knows if the universe is infinitely big or finite. I can guess at the second part about cooling. I think due to expansion, more volume the less hot everything will be. Same heat spread out further. But this is just a guess.

[@brien9648]

@@MrT------5743 Would that not imply then that the universe does have a set size? As there was a set amount of energy that came with the formation of everything? Does infinite density also implies infinite energy? This whole thing make my head hurt to think about.

[@MrT------5743]

@@brien9648 Yeah the whole notion of infinite anything is hard to wrap your mind around.

[@frasercain]

If the Universe is infinite, it was infinite at the beginning too. The observable Universe might have been only the size of a volleyball, the actual Universe was still infinite, even before inflation.

[@petergerdes1094]

Yes, but isn't the observable universe practically bounded by the time of recombination (eg mwave background) and can't we use variations in that to infer things about gravitational density from further away than that limit? But I guess that's only about the practical limit not the formal def of observable universe. Anyway this was a great Q&A

[@leonwilliams9589]

The only reason we are able to see close to the edge (“beginning”) is because the universe is expanding exponentially while the speed of light remains constant. Meaning, there is actually two parts to his answer. A. What you can detect, with linear detection equipment (limited by the casual propagation of light), out towards the edge of the observable universe (but never beyond it) is always the past. B. What’s actually there, and beyond it, is just more curved spacetime. The “observable universe” is a reference frame phenomenon. It’s not a physical edge to anything, even the propagation of gravity waves. The ability of these waves to propagate farther than the duration of this growing/shrinking barrier is just not possible.

[@petergerdes1094]

@@leonwilliams9589 Yes, I was pointing out that practically speaking our ability to observe events using em radiation ends with recombination in the early universe (event that produced mwave background) as before that the mean free path of photons is incredibly short (keep hitting electrons) so we can't easily see back to an earlier time using em radiation. However, the mwave background does encode information about the matter distribution at that time so we can infer info about how stuff that is further away (ie further in past than recombination) from variation in mwave background. Of course, as I note at end, that's only a practical limit on observability...and only observability in em ...if u go to other kinds of obs (grav waves) u can see back past recombination.

[@petergerdes1094]

@@leonwilliams9589 Or, more simply, in terms of em wavelengths our ability to see further is blocked by opaque shit at the time of recombination even tho the speed of light limit would theoretically let us see anothed 400, 000 more light years. But we *can* still use info about distribution of that opaque matter to infer things about the stuff that's in that 400k light year limit (tho not beyond that).

[@Erevos85]

Can a black hole be so massive that it could create its own miniature version of a Big Bang?

[@miinyoo]

Wow. 62 trillion dollars for a gram of highly reactive (with normal matter) substance is super risky. Fusion is hard enough and it only turns

[@absalomdraconis]

Also, a lot of products of M-AM annihilation don't cooperate with pressure chambers (e.g. neutrinos, though I think a neutral pion or something was the main culprit?), so if you want to maximize performance then you need to connive a way to get the uncooperative particles to shoot in the correct direction.

[@brick6347]

Could a crew dragon realistically do a moon mission? My understanding is that its shape and heat shield couldn't withstand entry at that velocity.

[@oldmandoinghighkicksonlyin1368]

Where would they poop for a week? That vehicle is only designed to hold people for a day or two at most.

[@MrT------5743]

@@oldmandoinghighkicksonlyin1368 Crew Dragon is alot bigger than the Apollo spacecraft and people were able to poop in that just fine.

[@ottovonottsville476]

Beyond the observable universe... I guess Frazer never heard of this: "The dark flow is controversial because the distribution of matter in the observed universe cannot account for it. Its existence suggests that some structure beyond the visible universe -- outside our "horizon" -- is pulling on matter in our vicinity." -Guess I'll look for a source with a little more 'depth'.

[@frasercain]

Planck data disproved the Dark Flow theory about 9 years ago. I could have explained that people once thought it was possible and then it was disproven. I'll keep that in mind for next time.

[@ottovonottsville476]

@@frasercain "2013, data from the European Space Agency's Planck satellite was claimed to show no statistically significant evidence of existence of dark flow.[5][14] However, another analysis by a member of the Planck collaboration, Fernando Atrio-Barandela, suggested the data were consistent with the earlier findings from WMAP."

[@ottovonottsville476]

@@frasercain "corresponds to the particle horizon at a distance of about 46 billion (4.6×1010) light years. Since the matter causing the net motion in this proposal is outside this range, it would in a certain sense be outside our visible universe; however, it would still be in our past light cone." -So I don't see how matter beyond what we can see wasn't affecting the matter we can.

[@CosmoPhiloPharmaco]

In 30 years? No way you'll still be doing this show. I bet 10 dollars.

[@frasercain]

I’ve been doing this job for 23 years so far.

[@PereBouSabria]

I never understood why astronomers say that if there was enough density of mass space would not expand because it would overpower dark energy. I don't quite understand the link between space itself and matter, in my mind the fabric of space-time should not care if plenty of matter or not. Mass attracts not only matter but also space? Weird! I think my confusion might be that the analogy of the fabric and the marbles might have its limitations

[@absalomdraconis]

Mass _doesn't_ attract distant matter _at all,_ it just attracts the space that the other matter is "sitting" in.

[@nosondre]

Can I help you sir? Why, yes. I’ll have the king size event horizon with a side of extra crispy singularity please…

[@silverstorm2735]

👍

[@petergerdes1094]

If we had a huge nuclear war would it be visible at galactic distances and, if so, have astronomers looked for such signatures?

[@frasercain]

That has been one suggested idea for searching for other civilizations. To scan for their nuclear wars.

[@petergerdes1094]

@@frasercain Thanks so much for the reply. That's super neat!

[@HughPryor]

Hang on! Every minute we have here corresponds to a fraction of a minute or must be a few seconds at the edge of the universe... in fact what is the red shift of the CMB?

[@frasercain]

The CMB is z=1000

[@HughPryor]

@@frasercain You are kidding me! So that makes every minute be less than 1/16 of a second of CMB action? We need to get the Slow Mo Guys onto this one! Oh wait...🤔

[@mattuk56]

Fraser if you are doing this show in 30 years you have to get a monocle so you can be like Patrick Moore.

[@frasercain]

Awesome idea. :-)

[@charleslivingston2256]

Pluto and Charon are too close to each other in mass to have their L4 and L5 points be stable for even negligible mass

[@xliquidflames]

How can the universe be 13.6b years old but the observable universe is 46b light years across? Furthermore, how can those be true while also the entire universe 93b light years across? I know space is expanding but I don't see how these numbers make any sense even if things are moving away from us.

[@virutech32]

pretty sure the observable universe is 93 billion & we have no clue how big the actual universe is

[@xliquidflames]

@@virutech32 Gotcha. I guess the thing I'm having trouble with is that we can see further than the universe is old? Does that make sense? It seems counterintuitive. Or is it the other way around? Maybe I'm not even explaining it right. That's how much I don't understand this.

[@virutech32]

@@xliquidflames far as i can tell that's just due to the expansion of space. Some far off photon from the CMB or what have you may have taken at most the 13 odd billion years it takes to get from there to here but the space in between has expanded by a lot. Which is why we calculate the edge of the cosmos to be 46 billion light years away but only see stuff from 13 or so billion years ago.

[@MrT------5743]

I don't have all the answers, but lets say you are looking at a galaxy that is 5b light years away. It took 5 billion years for that light to reach us and it has been moving away from us that whole time. So we can see only so far, but know those objects are further away than we currently see them.

[@raincheck5892]

Is there a way you could use quantum entanglement to take a picture millions of light years away and send it back?

[@virutech32]

Pretty sure that's just adding steps to an already difficult process since ud still need to send a camer millions of lights out & wait for the transmission to get back millions of years later. Last i checked quantum entaglement doesn't actually help with any part of that as it can't transmit any useful information FTL or anything.

[@frasercain]

Not that we know of. You need to communicate the state of entangled particles at the speed of light. Unfortunately, there's no way to get around the speed of light.

[@oldmandoinghighkicksonlyin1368]

Yes, but it'd take millions of years to set up the entangled particle first since you'd have to ship it there. Plus the information you get in return would be binary at best. An on/off switch a million light years away. The scale needed to gain any sort of data resolution, compensating for error correction, and what if something goes wrong at your end point? Ship out a technician and hope he's got enough food to last the journey? It's one of those projects that you'd undertake if you're a Type III civ and have FTL transportation. Currently, our human civilization has teetered on the brink of destruction for the last 10-12 thousand years. And our species has been around for around 500,000 to 2,000,000 years. Starting a project that takes MILLIONS of years to complete, you'd have to predict how human beings would evolve via Darwinism. Maybe we wouldn't even be around at the time of the project's completion, let alone be capable of comprehending the signals being returned. Perhaps our eyes would no longer be able to perceive the visual part of the electromagnetic spectrum due to a change in Earth's orbit because of a massive comet strike. Or we no longer use language to communicate because of a terrible calamity that caused a collapse of civilization.

[@raincheck5892]

@@frasercain I thought quantum entanglement was instantaneous… my bad

[@MrHarald75]

I have a question: what if dark matter does not exist and the outer stars of galaxies are just passing through them on very large orbits? ... and where is my nobel price?

[@lolmao500]

We should be doing a flying venus colonisation mission instead of a mission on mars. We could find an altitude on venus where the gravity and temperatures are the same as earth and astronauts could live in flying blimps in venus atmosphere.

[@jondoc7525]

Grow weed and sell it back on earth . Perfect sun etc . Start terraforming back somehow eventually . Release some bacterias that make oxygen abs survive somewhere there

[@PeterHaida]

Would there be any possibility that James the web telescope could see beyond our visible universe, I was thinking if there are theoretical universes/multiverse far beyond ours that are hundreds of billions of years old, do you think it would be possible for the light to penetrate our universe and be seen by the JWT.

[@alangarland8571]

The observable universe is by definition that part of the universe which is observable. now or ever. We won't see objects more distant because they are receding from us faster than light and always will be, (according to currently accepted theory). Cosmological expansion is not limited by light speed.

[@tomhools1605]

11:13 and yet your pal Robert Zubrin claims how fusion rockets could make interstellar travel possible.

[@frasercain]

It really depends on the speed you want to go. If you're fine with hundreds of years, fusion rockets might work.

[@tomhools1605]

@@frasercain Zubrin says that it would take about 40 years to the closest star using fusion, that fusion rockets would be 6000 faster than chemical rockets, but he is frequently unrealistic, although I gather that it is hard for "us" now to give definite answer.

[@seasonallyferal1439]

Shouldn't we be looking for life possible planets instead of techno signatures ? By the time we can interact they are likely extinct just from the odds.

[@mralekito]

I’m the guy who has said numerous times on your videos that we will not get to Mars this century - if ever. It’s too far away, too hard to get to, almost impossible to land, and basically impossible to survive there. It’s been 50 years since went to the moon. Mars is 100 years +

[@michaelpettersson4919]

Calculation the cost of anti matter today are rather pointless since it is obvius that today's technology are not going to be able to produce more then a handful of shortlived particles for the scientists to study. Then again aluminium used to be super expensive until advances in technology made the material literary dirt cheap. Over time we should be able to drop the cost but it will most likely never be "dirt cheap".

[@derivious2012]

rather than better denser fuel imagine better efficiency, if we could convert close to 100% the mass of a fuel to energy imagine the implications of travel e+mc2 etc.

[@frasercain]

That's antimatter. It's theoretically 100% efficient when smashed into matter and could absolutely get you to relativistic speeds. It's just expensive to make and tough to store.

[@ottovonottsville476]

Another rocket?? Why couldn't you just refuel the one you're in?

[@ocoro174]

fraser would you like to see a mockup for a modernized thumbnail for your videos for free? 😎 I am a professional graphic designer

[@Raz.C]

re - Fusion drives and interstellar travel I agree wholeheartedly with Fraser's conclusion. However, as a chemist with an excellent working knowledge of nuclear physics (as all good chemists do), I'd go even further! I'd say that "Fusion Drives" would be useless for interstellar travel AND intrastellar travel. In other words, a fusion drive would be useless for getting around the solar system. A fusion drive is NEVER going to be a good propulsion system. However, a fusion drive could make for a very good power generation plant for the spacecraft. So, if you could harness fusion energy, it would be wonderfully useful in providing electrical power to the spacecraft, however, the actual propulsion of that spacecraft would be better served by way of an Ion Drive, or a Plasma Drive. As it happens, Plasma Drives require enormous amounts of energy to run, so a Fusion Generator would be the ideal compliment to running a Plasma Drive.

[@CeresKLee]

I disagree! I see a black hole was a hole in the spacetime continuum. You cross the event horizon, you're gone and you never coming back. This is true for anything including light! We not only not know that is happen across that event horizon, we will never know. That makes it different than a star and unlike any other object.

[@classicalmechanic8914]

Hey Fraser, I think you answered wrong on the second question. It is true that we cannot directly detect objects beyond the observable universe through gravity, but we can detect them indirectly through distortions of orbits of objects inside obserable universe that are affected by gravitational objects outside of our observable universe. This does not violate physics because objects that are outside our observable universe are not necessary outside observable universe of the object whose orbit is distorted from our observer point of view.

[@adamtschupp9825]

Why are you always so pessimistic about humans living on other planets like Mars or the moon? Every time you talk about it, it seems like you just dismiss it out of hand "Oh it's hard so we should never do it" is such BS reasoning We should do it BECAUSE it's hard. Even if we fail, the lessons learned will still be valuable but you seem to be giving up even before we get to the starting line. And if we DO succeed living on Mars or the moon, it unlocks humanities ability to live on any world.

[@frasercain]

There's no reason to do it. There's no lasting benefit. I'm all for science stations like we have in Antarctica, but it's also the same reason nobody chooses Antarctica as their home. It's a difficult life with no benefit. I think that humanity will eventually live across the Solar System, but only when our technology trivializes the difficulties. And that's still centuries away in my opinion. And, gravity wells are for suckers. It'll be orbiting stations. :-)

[@JerrodleeJax]

Please stop with fairy tale answers based on unproven science.

[@frasercain]

This probably isn’t the channel for you. Fortunately you get to choose what you want to watch with your time.

[@MrT------5743]

Most of the stuff that he says that is unproven, he says that. It is not like he is saying things and claiming it all as absolute facts. But Like he said, You can choose to watch something else.