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I once saw in a reply to a comment to a youtube video, someone suggesting that as a fermi paradox solution, once civilizations get the ability to create near light speed spaceships, a few nutcases are likely to use the spaceships to destroy their own civilization by intentionally crashing them into planets while they are still going near the speed of light, killing all inhabitants of those planets as well as everyone in those spaceships.

Could near light speed spaceships be used to destroy a civilization, and if so could this be a great filter?

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    $\begingroup$ The difference between a near-lightspeed spaceship and a relativistic kill vehicle is wether or not you use the brakes. $\endgroup$
    – Burki
    Commented Jul 16, 2021 at 9:09
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    $\begingroup$ Perhaps they could tightly regulate their light speed spaceships, like nuclear weapons, so that it would take a whole government to misuse one, not a crazy individual. Perhaps they could spread their civilization out through an asteroid belt, so a single impact can't take it out. Perhaps they could build their cities miles deep under the surface of their planet, so an impact capable of wiping out surface life wouldn't be too bad. $\endgroup$
    – causative
    Commented Jul 16, 2021 at 11:00
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    $\begingroup$ No. With developed tech it is not likely a planet to be the only place for their civ. Space habitats quite universal out of planet solution. So as detection is possible of the process of acceleration, so then there are possibilities for countermeasures. $\endgroup$
    – MolbOrg
    Commented Jul 16, 2021 at 11:20
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    $\begingroup$ Remember the Kzinti lesson!! $\endgroup$
    – Joe Bloggs
    Commented Jul 16, 2021 at 11:29
  • $\begingroup$ Discussion: youtube.com/watch?v=O_XCB08OPw8 $\endgroup$ Commented Jul 18, 2021 at 2:51

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Edited to correct for a wrong reference energy

It's tricky.

The Chicxulub impact, which we can take as a reference for an extinction level event, delivered about $2 \cdot 10^{24}$ J of energy.

To deliver a similar amount of energy, you would need a 10000 ton ship traveling at 0.95 c, resulting in an energy of about $2 \cdot 10^{24}$ J.

For comparison, the ISS has a mass of just 419 tons, so you would need something like 500 ISS. For us is a lot, but for a civilization which can accelerate something at almost luminal speed maybe it's peanuts.

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    $\begingroup$ Or you could throw a 1 kg projectile and spare yourself a world ending ship... $\endgroup$
    – LuizPSR
    Commented Jul 16, 2021 at 12:51
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    $\begingroup$ Your figure for Chicxulub is only about equivalent to Tsar Bomba, some 7 to 8 magnitudes too low. $\endgroup$
    – Elukka
    Commented Jul 16, 2021 at 16:40
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    $\begingroup$ Relevant XKCD, which also demonstrates the exponential difference between 90% and 95% c. $\endgroup$
    – JBH
    Commented Jul 16, 2021 at 16:41
  • $\begingroup$ Agree with @Elukka. $10^{17}J$ of energy is tiny in the grand scheme of things. $\endgroup$
    – Harsha
    Commented Jul 16, 2021 at 18:52
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    $\begingroup$ @Elukka, you are right, I picked the wrong line in the reference. Haste makes waste. Now corrected $\endgroup$
    – L.Dutch
    Commented Jul 16, 2021 at 21:06
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Simply said, yes! A few KG of mass at near lightspeed would hit with forces many times that of an extinction event meteorite. A full space ship with hull, armor, passenger capacity, atmosphere, food+drink, equipment and cargo capacity going at near lightspeed would definitely be able to wipe out the civilization from a planet.

It might also has the means to protect against it. Notice the "armor" there. A ship going at near lightspeed will need protective measures, as hitting a dust particle is like a grenade if not more powerful going off while a pebble could turn your ship inside out. At such speed even air molecules would fuse to the exterior of the ship and create a nuclear reaction. The armor will likely be something else instead, like a field that disperses dust and micro meteorites before the ship passes. That would mean a planet would be able to use such technology to thward the near-lightspeed ship if not detect it in time and launch a bowlingball at lightspeed into its path causing the ship to desintegrate and spread its energy across space and the entire atmosphere of the planet.

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  • $\begingroup$ If the ship is traveling at near lightspeed towards you, then without having FTL, you won't detect it in time to do anything about it. $\endgroup$
    – vsz
    Commented Jul 18, 2021 at 17:31
  • $\begingroup$ @vsz if you move at 95% of the speed of light, then a beacon that detects your passage and sends a lightsignal will warn them with 5% margin on the ship. So if you get detected at the distance of the Sun the planet has 21 seconds to react. That is assuming they dont see the light of your ship achieving near-FTL earlier or detect your method of dispersing the materials in front. Keep in mind that such a ship needs to send signals in front to map any debris too large and take evasive action in advance, that would need to travel at lightspeed and be detectable long in advance too. $\endgroup$
    – Demigan
    Commented Jul 19, 2021 at 4:27
  • $\begingroup$ A vessel traveling at .95% will still interact with the space along its flight path and do so from the moment of launch. At low speeds these interactions would be trivial but at its final (high C) cruising velocity? A 10,000 ton ship traveling at .95C should generate SOME kind of 'bow wave' as it impacts gas molecules etc in the interstellar medium. That should in turn should produce some kind of EM emission which would speed ahead of the ship. So on say a 50 year .95C voyage you might get a couple of years warning IF you knew what to look for. Or am I wrong? $\endgroup$
    – Mon
    Commented Jul 20, 2021 at 1:27
  • $\begingroup$ @Mon since these interactions would likely destroy any type of armor even if we assume we can use any metamaterial as armor the proposed protection seems likeliest: try to detect any material in the way and somehow push it aside (lets say laser ablation) before the ship arrives. That still means the ship has to send out signals at lightspeed to detect anything in front in time, which has to be a strong beam and can be detected. $\endgroup$
    – Demigan
    Commented Jul 20, 2021 at 4:29
  • $\begingroup$ I was thinking more in terms of magnetic shielding for charged particles and/or a plasma shield of some sort. Regardless of the technique if you have some random hydrogen molecule wandering along in the interstellar slow lane and it gets T-boned by a 10,000 ton ship traveling at .95C there should be a reaction as it suddenly gets accelerated to a high % of the speed of light. And that should (I thin) include some kind of high energy emission in the EM spectrum which will run ahead of the ship as part of a 'halo' of similar emissions from other impacts. The shield would probably emit to. $\endgroup$
    – Mon
    Commented Jul 20, 2021 at 12:06
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It is possible for a civilization to destroy itself. We believe our nuclear arsenals are an example. It is believed that firing all of our nukes would change the climate enough to kill us off.

It is also possible for a near-lightspeed vehicle to kill off everything on a planet. The other answers cover this perfectly.

The hard question is whether a civilization that has near-lightspeed traffic could ever possibly limit itself to one planet. Yes, one nutjob might be able to take out a planet, but not an entire Class II or Class III civilization.

The other question would be whether such an advanced civilization would have trouble colonizing new planets. We search for Earth-like exo-planets because that's what we feel we'd need to survive. An advanced civilization may have sufficient teraforming capabilities to widen the set of possible planets to colonize after someone gets a DUI at almost the speed of light.

The underlying mathematical principle is known as the Edge of Chaos. The idea is that there are some systems that are insanely ordered. Others are insanely unpredictable (i.e. chaotic). But the transition is kind of mushy. The Edge of Chaos is a hypothesized region dominated by the interplay between order and disorder. Those who study this concept find that living organisms and civilizations have a curious tendency to sit in this edge of chaos region. Its the region of maximum complexity.

If you assume that a civilization must destroy itself because it isn't perfectly ordered, you miss out on the strange tendency of civilizations to persist way longer than they should at first glance. I don't know how old you are, but from what I have read, every generation comes to the conclusion that the younger generation will probably be the last generation in the civilization. Yet every younger generation somehow rises to the challenge (so far!)

Now if you want to talk about infinities, its hard. A chaotic system will always destroy any order in unbounded time. An ordered system will always persist for unbounded time. The behavior of a system on the edge of chaos is... tricky. You typically can't tell if it will go one way or the other.

Nietzsche spoke of this, in different words, in Thus Spoke Zarathustra. Feel free to read it if you want a more philosophical take!

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I enjoyed Goodies' idea with the marbles, but I don't have any rep yet so I can't comment. I came up with a hard-sci-fi example just because I'm that bored tonight. If you wanted to do it right, and if you could accelerate marbles that fast, such a concentrated attack wouldn't need nearly the energy a meteor does. Let's talk about a marble traveling at a speed very close to the speed of light (like 0.99999c, around 10^12 MJ). It would really only take one. At such speeds, collisions occur on a particle-by-particle basis and they need to be handled from a nuclear physics perspective (hey, that's why I do. Let's have some fun!). In short, in the center-of-gravity system, the incoming nuclei are approximately infinitely massive compared to the air molecules, so considering deflection and slowdown, it's pretty much like the air is just not there. It's like shooting bb guns loaded with ants at an aircraft carrier. Sure, you may scratch the paint, but you're not going to change the direction of that ship (marble) even with a billion ant guns (air molecules). The point is, it will spread out a bit, but ALL of that mass is going to impact the planet's surface pretty much at the exact point you were aiming. Also, it doesn't really matter what the marble was originally made out of, since those nuclear interactions are going to quickly convert it into fundamental particles anyway. Marbles that started off as tungsten, steel, wood, chalk, or whatever, are all going to be approximately the same blob of plasma by the time they reach the surface. The only things that matter are the mass of the marble and its total energy (velocity).

Now here's the neat part. After it strikes the planet's surface, those collisions also occur on a particle level. The huge boom, splash, fireball, etc. like from a conventional projectile (asteroid) are all caused by friction and chemical reactions, so they just don't happen. To continue the sci-fi part, if our original marble was fast enough, there isn't enough planet to stop the infinitely-massive plasma-marble which just hit it. Instead, it simply starts burrowing a marble-sized hole which continues for a couple thousand miles. Deep enough to reach the planet's molten outer core. On its way through the planet, our marble transferred enough energy through those nuclear collisions to cause some really neat stuff. Imagine setting off a nuclear bomb halfway through the earth, the width of a dinner plate but 1,500 miles long. We can't produce sustained nuclear chain reactions with our marble, but we have created enough micro-chain-reactions to multiply the initial deposited energy a thousandfold. The resultant radioactive heating has melted everything within, say roughly thirty feet based on the typical size of the cavities from underground nuclear testing. Plus, we have a superheated plasma crust a couple millimeters thick that will heat things up even more. Boiling metal magma, anyone? All of that--let's call it superlava just for fun—is immediately going to start squirting out of the hole on the surface. After a few seconds, hydraulic pressure from deep inside the earth will have increased the velocity of the superlava jet to perhaps a few thousand miles per hour. THEN you get the fire storm noone has dreamed of before. Not the relatively cold mushroom cloud from a nuke, mind you. Pure liquid fire, hundreds of miles high, shaped something like one of those spinning tops, but inverted. Receiving an endless supply of energy and magma from the earth's core, this megavolcano--no, gigavolcano—will continue erupting for weeks, at which point the resulting ash cloud has completely enveloped the planet. Mass leakage and raining superlava has caused the oceans to boil for hundreds of miles around the impact point, which does eventually result in the mile-high tsunamis we all love so much—just a few days too late for Hollywood's tastes. So yeah, say bye-bye to every living thing on the planet.

Oh, and the backup plan—that space station in orbit full of survivors? Kiss all your LEO objects goodbye. If the EM pulse from the marble's initial impact didn't take it out, their orbital path will eventually take them right through that superlava geyser. Imagine frantically trying to survive in space for days without power, only to get melted. Bummer, man.

Yeah. That was fun. It's obviously quite fictional, but I did perform a reasonable estimate of the energy required to poke a hole into the earth's core, and calculated the energy needed to raise everything in a 10-m-wide column to boiling temps (appx 3000K). So at least that part of the physics is consistent within a factor of a couple :).

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  • $\begingroup$ Very dramatic. Welcome Fazeal, we invite you to take our tour and refer to the help center as and when, for guidance as to our ways. Enjoy the site. $\endgroup$ Commented Jul 17, 2021 at 8:20
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once civilizations get the ability to create near light speed spaceships

To create those speeds you need lots of energy. To be precise, to accelerate a 1k ton spaceship to 0.95c you need 10^17 MJ which is equals to ~500 times the yearly primary energy consumption of the world. A civilisation that can effort these energies can likely harness great portions of the energy of their star already.

a few nutcases are likely to use the spaceships to destroy their own civilization by intentionally crashing them into planets

Destroy.. their own civilisation? Why would this solve the fermi paradox then? I think you mean other civilisations? And even then, accelerating something to near speed of light still takes a large portion of energy that your civilisation needs to achieve first. It won't be like: "hey everybody suddenly has access to lighspeed vehicles now": It still takes a significant amount of energy that a civilisation will understand to distribute in some organized way, and certainly not "illy willy" to some "nutcases".

Could near light speed spaceships be used to destroy a civilization

Yes, although this is just another way of saying "can large energies, in which ever form, destroy a planet". Yes, but you could as well shoot a giant laser, or focus the light of your star to some planets etc. that might be easier if you want to destroy something.

if so could this be a great filter?

Having this done by "nutcases" is not a very credible explanation for the great filter in my opinion, rather it is more credible to be an effort of the whole civilisation. Kurzgesagt has a nice video on this.

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    $\begingroup$ "Why would this solve the fermi paradox then?" - F Paradox or that great filter thing is about die out of some civ for some chracteristic reason(which repeats at other civ) thus effectively preventing them conquer and totally inhabiting their own galaxy. So more often it about causes of selfdestruction, to explain why they development stopped. $\endgroup$
    – MolbOrg
    Commented Jul 16, 2021 at 11:13
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    $\begingroup$ @MolbOrg It is usually spoken of in terms of destroying your own civilization, yes, but really one civilization destroying others and then hiding would also solve it, which is probably the context the author of this answer is thinking it. $\endgroup$ Commented Jul 16, 2021 at 12:45
  • $\begingroup$ Currently nukes could still be one of our great filters, if any country is crazy enough and in a corner they might cause a chain reaction that destroys us. However such near-FTL ships could be in the hands of many more people than current nukes are. This could be a plain human error or a computer failure causing a ship to crash, but considering the complete instability of mankind during our first pandemic there is precedent for people to do something like this. Regardless of them doing it to get rid of a "deep state" or 12+G connections or for God to create a clean slate doesn't matter. $\endgroup$
    – Demigan
    Commented Jul 16, 2021 at 14:27
  • $\begingroup$ @BenjaminHollon Yes, as I said, most, not all - people put great deal of fantasy in all sorts of scenarios. $\endgroup$
    – MolbOrg
    Commented Jul 16, 2021 at 15:26
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    $\begingroup$ With enough people around eventually a nutcase will manage to seize control of a starship. $\endgroup$ Commented Jul 18, 2021 at 16:33
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kamikaze won't work, the planet is never reached

Agree with Demigan ship armor would be needed, but my answer is no for that reason. In interstellar flight, near c impulse speed can only be used in deep space. Your ship would never reach a planet with near c speed. It will have disintegrated underways, as a result of collisions and penetrations caused by much smaller, sometimes microscopic objects, which are abundant in the vicinity of planets. Shield or armor against that would become too heavy, making it impossible to accellerate the ship. When collistions happen close to the planet, I wonder if the ship's debree will have lost enough speed to avoid damage, but I doubt if debree would wipe out civilisation.

use titanium marbles !

A more sensible and probably much cheaper scenario involving a near-c bombardment would be to hit the planet with a few hundred much smaller, very rigid objects, traveling at say, 96% or 98% speed of light. For example, titanium marbles 10-50 grams each, perfectly spheric and polished. About half of them will reach the planet..

These objects could be launched above the poles of the planet. That is the only possible path, else too much dense regions would have to be crossed. Say the impact will take place latitude 85 degrees in arctic and antarctic regions, about 60 degrees vertical. A properly targeted "cone" of these titanium marbles impact the planet surface simultaneously. The resulting shockwave could devastate the planet's crust and everything on the surface.

enter image description here

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    $\begingroup$ Question though: wouldn't the balls already be vaporized in the upper atmosphere as they quite literally crash into it? The resulting shockwave would still ripple from up to down and possibly tear apart most structures on the surface anyway. $\endgroup$
    – Demigan
    Commented Jul 16, 2021 at 14:20
  • $\begingroup$ Maybe some coating over the titanium core would help ? But in principle, you may be right.. the projectile has to be protected somehow, against melting too quickly. When it reaches the planet in fluid state, the effect would be considerable, but certainly much weaker. When it evaporates.. well.. then it's gone. My scenario is statistics anyway, if you send 100, half will reach the planet, the other half.. is lost. If you send a ship.. it's too big and fragile, it will always be hit and imho never reach the planet surface, because of collissions underways and (indeed) atmospheric friction. $\endgroup$
    – Goodies
    Commented Jul 16, 2021 at 23:19
  • $\begingroup$ Another note about your remark: we would actually need to calculate these things.. but you must take into account an object moving at a speed of >0.95c will only be in the planet atmosphere a few milliseconds to warm up ! and when it evaporates.. it would have transferred its kinetic energy into the atmosphere.. what would be the effect of that.. $\endgroup$
    – Goodies
    Commented Jul 16, 2021 at 23:25
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    $\begingroup$ Its not really about a coating. I'll let XKCD explain: what-if.xkcd.com/1 $\endgroup$
    – Demigan
    Commented Jul 17, 2021 at 6:41
  • $\begingroup$ Titanium?? Did you mean Tungston? $\endgroup$
    – JDługosz
    Commented Jul 20, 2021 at 23:26
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If you have near-lightspeed spaceships, then it seems likely that the civilization is not confined to a single planet. A lone suicide ship cannot wipe out the fleets of orbital habitats that are orbiting other planets and stars, plus the many colonies on other planets, moons, and asteroids.

The nutter is a tragedy of epochal proportions, but the civilization will muddle on.

Oh, and perhaps it's also possible to lock the door of the flight deck so the nutter cannot simply stroll in.

Perhaps the controls can be locked, or set to respond only to licensed and authorized pilots. Perhaps the pilots can be examined by a psychologist before duty shifts (Heinlein mentioned that in 1953) as part of their authorization process.

Perhaps Traffic Control can override the pilot controls. A safeguard designed in centuries ago, when another nutter had to be blown out of the sky

Perhaps the planets still have defenses against nutters ignoring Traffic Control. Perhaps those defenses are already primed and coordinated since nutters happen in every generation...so this isn't the first (or last) one.

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  • $\begingroup$ Sure, a kamikaze action would be against safety regulations ! a deadly course into a planet could be inhibited in electronics. That would prevent it, EXCEPT when kamikaze would be adopted as strategy, like Japan did. Fleets orbiting the planet would have to intercept. They should be able to (very) precisely predict the trajectory of the incoming ship. In a matter of seconds when the ship is cloaked. It is like creating an interplanetary Iron Dome against missiles traveling near light speed. Maybe that could be built one day, but near c travel (as such) could be realized much earlier ! $\endgroup$
    – Goodies
    Commented Jul 18, 2021 at 10:28
  • $\begingroup$ @Goodies yes, that's what the final paragraph is for. It's really up to the OP to decide on the capabilities of their world. $\endgroup$
    – user535733
    Commented Jul 18, 2021 at 10:29
  • $\begingroup$ It need not be a rogue nutter. Nutcases can be official captains following official strategy. It could be an act of war. Ship could even be abandoned just before impact.. I think an intercept in the Iron Dome way would be difficult.. how to hit the incoming ship with anything ? it could require a planetary shield of some kind, being active over a range of thousands of miles. $\endgroup$
    – Goodies
    Commented Jul 18, 2021 at 10:33
  • $\begingroup$ The Question says "a few nutcases are likely to...." The OP did not ask for using near-C ships as weapons of war, which has been asked before and has a somewhat different set of answers. $\endgroup$
    – user535733
    Commented Jul 18, 2021 at 10:35
  • $\begingroup$ When the planet is not defended by a permanent shield, and the impact would be an unofficial and unawaited mission, they would not see it coming in.. there is no defense at all against it. When it can hit the planet (improbable, see above) there would be devastation. 0.92c may be enough to cause the atmosphere to explode, or tear apart the crust.. the ships mass is a multiplier.. $\endgroup$
    – Goodies
    Commented Jul 18, 2021 at 10:39
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No, this is not a filter... or at least not directly.

Assuming we're talking about actual kinetic motion, the amount of energy required to accelerate to such a high speed is truly ridiculous. If someone really wanted to destroy the planet - or at least scrub it clean of life - then it would be simpler to directly apply that energy to the planet itself. The development of a power source for the ship therefore is far more dangerous to the planet than the ship itself. Yes, some grand Lexx Luthor-esque evil mastermind might threaten to redirect a ship to destroy the planet, but it's far more likely that a capable zealot would actually get the job done just by blowing the reactor.

Comic-book villains aside though, it is conceivable that Murphy's Law might result in an accidental collision between a near-C ship and a planet... but the odds are really against it. Hitting a target as small as a planet from any reasonable distance is really, really hard to do on purpose. To further reduce the chances it's likely that the ships always navigate above the ecliptic, and only vector towards a planet during the final phase of the journey. The ships have enough power to not need to use the sort of optimized trajectories we're used to... and of course the ships would be absolutely forbidden from pointing too close to a planet while travelling at high speed, since there will be plenty of nervous people who'd rather give up on space than see their homeworld destroyed by accident.

And then there's the defensive measures that could be used to prevent the impact, which gets a little easier with access to unlimited power. Whether that means shifting a bunch of mass into the path of the incoming ship or shooting it with lasers or whatever, the same power source that enables the ships to exist also enables countermeasures against them.

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You do have a heating problem with the ship.

Interstellar gas density is about 1 atom of H per cubic centimeter. There are 30 billion cm in a light second.

So you are hitting 30 billion / 6 * 10^23 = 5 * 10^-14 grams of H.

Let's ignore relativistic effects right now. Our ship is near c. The newtonian energy of 10^-14 g at c is 1/2 10^-14 * (3*10^9)^2

= 45 * 10^4 W/cm2 or 45 * 10^8 W/m2 4.5 GW/square meter. And that's ignoring relativistic effects.

Marbles at near C speeds aren't happening. You need a strong arm to keep those hydrogen atoms away. A strong, hairy tattooed arm.

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  • $\begingroup$ Fazeal says otherwise... at such energy, you get nuclear interactions and can ignore chemical interactions. You give the energy loss of passing through the hydrogen (if "collisions" did take place) but did not show how much that will slow it down. "ignoring relativistic effects" is a non-starter; most of the energy will be in mass. $\endgroup$
    – JDługosz
    Commented Jul 20, 2021 at 23:35

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