Bad Astronomy's BAD Facts and Points made on his TV show are really BAD! [Archive]

pzkpfw

2010-Oct-07, 05:17 AM

Not having seen this episode, I may well be corrected, but I strongly suspect you missed the point.

G forces don't just come from gravity - they come from acceleration in general.

The G forces a fighter pilot experiences, for example, don't come from Earths gravity - they come from the manouvers made by the plane. e.g. the tighter and/or faster a turn (in any direction*) is made, the more force the pilot will feel.

wiki link: http://en.wikipedia.org/wiki/G_force

The issue with getting humans far out into space, is that the distances are very very large. To get anywhere interesting will take huge speeds. To get to those huge speeds will take very large acceleration applied over a very large time. That will likely do "bad things" to humans.

(* Edit: to pre-nit-pick myself, Earths gravity will affect the g forces the pilot feels - depending on the direction of the turn. But that's beside the point - when a pilot blacks-out due to doing a 10 g turn - those 10 g's were clearly more than the pilot feels from Earths gravity alone, when standing still on the runway).

Van Rijn

2010-Oct-07, 08:33 AM

I'm watching it now, and I have to say I'm having a problem with his argument.

He first talks about it taking a year or more to reach Mars at 2Gs? I think that's an editing mistake: I believe he's talking about reaching escape velocity then coasting for most of the flight to Mars, but that wasn't clear as said. If you could manage 2G constant acceleration, flight time to Mars would be measured in days.

Then he talks about multiple Gs to go between the stars, apparently to reduce experienced crew time. However, if you could constantly accelerate at 1 G, you could reach the center of our galaxy, or the Andromeda galaxy, in a few decades ship time, so I don't see G forces being a major issue for a humanoid species (well, perhaps a problem if they somehow come from a very low G environment). The bigger issue is the energy requirement for constant acceleration - the energy requirements get insane. Also, high relativistic velocities are tough on spacecraft (even running into hydrogen atoms becomes a serious danger).

I think you can make a bigger argument about the problems of long crew flight times, though there are ideas for physically possible solutions (robots, life extension, biological stasis, generation ships, or a few other ideas).

slang

2010-Oct-07, 10:41 AM

If anything, the lack of g forces will (and does!) cause problems.

Darkchilde

2010-Oct-07, 11:47 AM

Any accelerated frame of reference is indistinguishable from a gravitational field, and this is a basic feature of general relativity. So, any accelerating vehicle will produce G forces, and those might be significant, and the human body will be crushed at very high G's. I don't remember how many G's a human body can sustain before literally being turned into pulp, at least internally.

Cougar

2010-Oct-07, 12:00 PM

This guy doesn't know....

I'm watching it now....

Do I even want to know who or what you guys are talking about?

NEOWatcher

2010-Oct-07, 12:49 PM

[snide remark said in jest] Do you know what board you are on and who was the author of "Bad Astronomy" and what his latest project is?[/snide remark]

Cougar

2010-Oct-07, 01:10 PM

[snide remark said in jest] Do you know...

Oh, how snide! :rolleyes: Actually, I do know who authored Bad Astronomy. But he corrects bad astronomy, not contributes to it. So what is this upstart OP going on about?

NEOWatcher

2010-Oct-07, 01:14 PM

I agree questioning the "what" (although it sounds like some preconceptions), but I was referring to the "who".

loglo

2010-Oct-07, 01:17 PM

Space travel is not astronomy so obviously the OP is incorrect when he says the BA is doing b.a. :)

neilzero

2010-Oct-07, 01:24 PM

Months of one or more g is necessary to get to Centauri in 3 years or less, of ship time = about 6 years back on Earth time, but there is no need to experience more than one g if 5 years ship time is the plan, except for a few minutes at lift off from Earth, and minutes before arrival. The Centauri planet, if any, could have more than one g. There is at least a slight possibility that ET finds two or more g comfortable. Technology we will have soon will likely make most of the trip at 1/10 th g or less and take many centuries both ship time and back on Earth time = impractical.
To a planet 20 light years away, over one g is necessary for minutes instead of years, unless you plan to get there in less than 5 years, ship time. Van Rijn explained excellently. Neil

Swift

2010-Oct-07, 01:45 PM

As this post doesn't seem to be a question, I've moved the thread.

By the way, welcome to BAUT HowBadisBadAstronomy. You must be passionate about this to have picked that as your user name.

R.A.F.

2010-Oct-07, 03:31 PM

I don't see G forces being a major issue for a humanoid species...

I agree, although it was a good "excuse" to fly on an F-15. :)

IsaacKuo

2010-Oct-07, 04:03 PM

I agree, although it was a good "excuse" to fly on an F-15. :)
F-16. ;)

And I think it's inexcusable. As Van Rijn noted, 1 gee is enough to get to the Andromeda Galaxy within a few decades of ship time. Human beings are capable of somehow surviving exposure to 1 gee for decades at a time; aliens might be able survive it also. Acceleration isn't the limitation.

Phil is guilty of bad astronomy--and yes, the physics of relativistic time dilation and the scales of time and distance in the universe are indeed astronomy.

He also missed out on the opportunity to discuss the real challenges involved in interstellar travel--things like the speed of light, the mind-numbing distances involved, the rocket equation, the heroic amounts of kinetic energy involved at relativistic speeds...

R.A.F.

2010-Oct-07, 04:31 PM

F-16. ;)

Yeah, I knew it was either a 15 or 16...figured I had a 50/50 chance of getting it right.

mike alexander

2010-Oct-07, 05:08 PM

This is a case where a link of some sort would be quite helpful...

Van Rijn

2010-Oct-07, 05:40 PM

Oh, how snide! :rolleyes: Actually, I do know who authored Bad Astronomy. But he corrects bad astronomy, not contributes to it. So what is this upstart OP going on about?

This is a case where a link of some sort would be quite helpful...

Oh, sorry, this is in reference to his second Bad Universe episode on Discovery channel, discussing aliens and alien attack ideas. I didn't notice that it hadn't been mentioned in thread.

Noclevername

2010-Oct-07, 07:29 PM

I saw the episode last night and noted the same problems-- I suspect a lot of unjudicious editing took place behind the scenes (something Phil would probably have little control over) and that the parts that made scientific sense wound up on the cutting room floor because scientifically illiterate suits thought it was "too complicated" for viewers (meaning they didn't understand it so they didn't see how anyone else could. )

eburacum45

2010-Oct-07, 09:09 PM

Short segment here.
http://dsc.discovery.com/videos/bad-universe-jet-jockey.html

I'm a bit disappointed.

I think that his point about the high acceleration is based on the idea that present-day spacecraft do most of their acceleration in rapid burns. The only types of spacecraft that are currently in use or on the drawing board which are capable of long, slow acceleration times are ion-driven craft and solar sails, and neither of those will get you to the Moon in 3 days. But fission, fusion, antimatter or beamed propulsion concepts could allow quite fast interplanetary journeys without any need for excessive acceleration.

Phill really needs to read more speculative fiction or something.

IsaacKuo

2010-Oct-07, 09:48 PM

I think that his point about the high acceleration is based on the idea that present-day spacecraft do most of their acceleration in rapid burns.
No, he goes on about how unthinkable it would be to live with such high accelerations for months or years.

Sorry, there's just no way to excuse Phil here. What he says is just too wrong. There isn't any part which is even close to correct.

His fundamental message is wrong. Phil claims that acceleration is the problem. Bluntly, it isn't. This is not just a matter of editing. He explicitly says it's acceleration rather than speed which is the problem.

Also, we can nitpick all day (turnabout is fair play), and note that Phil's claims are riddled with bad astronomy.

For example, it takes less than three hours to get from Earth to the Moon at 2 gees, not three days. It takes less than four days to get from Earth to Mars at 2 gees--even at maximum opposition--not a year.

The basic idea that you need high accelerations sustained for long periods of time to get around in space is simply wrong. It's wrong on a big picture level. It's wrong on a small detail level. It's wrong all around.

Phill really needs to read more speculative fiction or something.
What he really needed to do was apply some basic physics equations for a reality check.

He should have applied d = 1/2 a t^2 to estimate how long it would take to get to the Moon and Mars at 2 gees (modified for switching from acceleration to deceleration at the halfway point). It would have taken maybe 5 minutes for a simple BOE calculation.

Then, after his eyes returned to their sockets, he could have a nice little "bonk one's own forehead" moment before rewriting this large chunk of the show.

swampyankee

2010-Oct-07, 11:12 PM

Shortly before Phil Plait went for his F-16 ride, he nattered on about how traveling longer distances in reasonable time would require uncomfortably high accelerations. This set my physics nerd teeth on edge; the need for high acceleration is limited to the time needed to get away from the surface of Earth. They are not required for the travel between planets -- hence the idea of ion propulsion and solar sails -- nor are these high accelerations required for travel between stars.

mike alexander

2010-Oct-07, 11:47 PM

I agree with Isaac K and others (including the OP). Phil totally jumped the shark on this one. And Whoever said he needs to read some SF was on the mark. This wasn't a bad editing job, it was what Arthur Clarke called the Failure of Imagination (find a copy of the excellent Profiles of the Future). Along the lines of people who said Man would never fly, or ever send a rocket to the Moon. Really, really bad, no excuses.

I think he just wanted to cage a free ride in an F16.

R.A.F.

2010-Oct-08, 12:38 AM

What would have been the point of Phil flying on the F16, if the idea of acceleration hadn't been mentioned first? Perhaps Phil was offered the F16 ride, and a reason to justify that ride was then "invented"...but I really hate to speculate...wish Phil would just post to the board and clarify this.

Van Rijn

2010-Oct-08, 01:10 AM

What would have been the point of Phil flying on the F16, if the idea of acceleration hadn't been mentioned first?

Well, there are the claims about alien spaceships instantly accelerating or making extreme turns at high speed in the atmosphere. I think you could work it in that way, showing the problem.

As I mentioned in the other thread, there is discussion on BA's blog. Here's BA's comment:

http://blogs.discovermagazine.com/badastronomy/2010/10/06/bad-universe-contest-winner-and-some-skepticism-for-free/#comment-315910

Swift

2010-Oct-08, 02:20 AM

This wasn't a bad editing job, it was what Arthur Clarke called the Failure of Imagination (find a copy of the excellent Profiles of the Future).
Just a ditto, but yes, read it, a great book. I first read it 40 years ago and still think about it.

whimsyfree

2010-Oct-08, 04:32 AM

This wasn't a bad editing job, it was what Arthur Clarke called the Failure of Imagination (find a copy of the excellent Profiles of the Future)

I haven't read the book, but a failure of knowledge, surely. The calculations are simply kinematics. Anyone with basic arithmetic can multiply a large acceleration, say, 2g, by a long time, say a month, and get an enormous velocity.

eburacum45

2010-Oct-08, 09:24 AM

The section on high-gees would have made more sense if coupled to a discussion of the impossible physics that some UFOs seem to display. No matter how advanced a civilisation is, it will still have to deal with inertia and conservation of momentum. But prolonged high-gee acceleration is not required for interstellar travel, or for rapid interplanetary travel (except, perhaps, when leaving the gravity well of a planet).

whimsyfree

2010-Oct-08, 10:00 AM

The section on high-gees would have made more sense if coupled to a discussion of the impossible physics that some UFOs seem to display. No matter how advanced a civilisation is, it will still have to deal with inertia and conservation of momentum.

If they have enough exotic matter in their craft, these may not be a problem. Not that I believe in exotic matter.

But prolonged high-gee acceleration is not required for interstellar travel, or for rapid interplanetary travel (except, perhaps, when leaving the gravity well of a planet).

For aliens with a compact object in their system a brief period of high gees might be optimal, to get the most out of the Oberth effect.

IsaacKuo

2010-Oct-08, 10:31 AM

For aliens with a compact object in their system a brief period of high gees might be optimal, to get the most out of the Oberth effect.
The Oberth effect would not have a significant effect for useful interstellar travel speeds, unless that compact object were a black hole, or maybe a neutron star. Even then, you would need accelerations on the order of 100 million gees to use the Oberth effect. Plausibly, alien biology isn't going to be able to deal with that sort of acceleration. Heck, alien robots plausibly couldn't handle it.

So, if they want to use the Oberth effect it would be indirectly. They could use some sort of system to use the Oberth effect to accelerate dumb particles (like ions shooting out of a particle accelerator in tight orbit), and those dumb particles are deflected by a magsail for thrust. The starship doesn't ever get very near to the black hole, nor does it need to deal with very high accelerations.

Nereid

2010-Oct-08, 11:49 AM

The worst thing about the 'gs' bit (etc) is that it does immense damage to the BA's reputation ... it is exactly this sort of misrepresentation (and worse) that he so strongly criticised in the website he started (and which gave him his name). Even worse is his - to me, very lame - excuse for it (see Van Rijn's post for a link to it); when you're in a hole, stop digging.

whimsyfree

2010-Oct-09, 08:16 AM

The Oberth effect would not have a significant effect for useful interstellar travel speeds,

How do you know what are useful interstellar travel speeds?

unless that compact object were a black hole, or maybe a neutron star. Even then, you would need accelerations on the order of 100 million gees to use the Oberth effect.

I believe you just made that up.

Paul Beardsley

2010-Oct-09, 10:48 AM

This thread should be cited whenever somebody claims that BAUTers always close ranks, or whatever.

Daggerstab

2010-Oct-09, 11:22 AM

In such cases, I usually cite the whole "Space Exploration" section. :)

IsaacKuo

2010-Oct-09, 11:40 AM

How do you know what are useful interstellar travel speeds?
I consider useful interstellar travel speeds to be greater than 10% of the speed of light. Below this, travel times are on the order of centuries. I do not consider travel times on the order of centuries to be useful, because a technological species can be expected to advance enough in that time to send a mission that will overtake the original slow mission. Therefore, it makes more sense to simply wait for technology to improve. Waiting makes the mission arrive sooner.

(I have explained my ideas for single stream and double stream propulsion on this forum. These methods could provide practical interstellar mission cruise speeds of greater than 60%c, although I feel the sweet spot for early missions to Alpha Centauri is around 30%c.)

I believe you just made that up.
Please. You could give me the benefit of the doubt and ask for my justification.

In fact, I have contemplated using the Oberth effect of black holes, neutron stars, and white dwarfs. Especially white dwarfs, because unlike the other two they're quite common and there are quite a few within a stone's throw of our own star system. I actively contemplate what sort of star systems would be useful for us or aliens to exploit, and specifically how.

Anyway, the problem with using the Oberth effect for extremely high speeds is that you spend extremely little time close enough to the black hole or neutron star to take advantage of it. To get a boost on the order of 10% of c, you need to get in to where the escape velocity is significantly greater than 10% of c. And you need to do all of your acceleration within that zone. So, you're zooming through this deep part of the gravity well at perhaps 100,000km/s. You need to do all of your acceleration within about a km, so that gives you only 1/100000 of a second to accelerate. You want to accelerate on the order of 10,000km/s, so you need to accelerate on the order of 100 million gees.

So--the lesson of the day is, if someone gives an actual number, your first assumption should be that he did some (possibly wrong) calculations to get that number. Or looked it up on the internet. Either way, the first assumption should not be that he just made it up.

whimsyfree

2010-Oct-12, 01:39 PM

I consider useful interstellar travel speeds to be greater than 10% of the speed of light. Below this, travel times are on the order of centuries. I do not consider travel times on the order of centuries to be useful, because a technological species can be expected to advance enough in that time to send a mission that will overtake the original slow mission. Therefore, it makes more sense to simply wait for technology to improve. Waiting makes the mission arrive sooner.

I was considering speeds more of the order of 0.1 to 1% c. We don't know what the maximum practically attainable speed is, or how far they need to travel. Their target might be a companion of their primary. For general interstellar travel, the optimal speed might be lower than 10%c, depending on their objectives. For example, if the budget for launching interstellar vehicles is dominated by the energy, aliens could launch around 100 1% c craft for each 10%c craft.

Please. You could give me the benefit of the doubt and ask for my justification.

I'm sorry, but you must admit that big round numbers like "100 million" are not very believable.

In fact, I have contemplated using the Oberth effect of black holes, neutron stars, and white dwarfs. Especially white dwarfs, because unlike the other two they're quite common and there are quite a few within a stone's throw of our own star system. I actively contemplate what sort of star systems would be useful for us or aliens to exploit, and specifically how.

Anyway, the problem with using the Oberth effect for extremely high speeds is that you spend extremely little time close enough to the black hole or neutron star to take advantage of it. To get a boost on the order of 10% of c, you need to get in to where the escape velocity is significantly greater than 10% of c. And you need to do all of your acceleration within that zone. So, you're zooming through this deep part of the gravity well at perhaps 100,000km/s. You need to do all of your acceleration within about a km, so that gives you only 1/100000 of a second to accelerate. You want to accelerate on the order of 10,000km/s, so you need to accelerate on the order of 100 million gees.

That doesn't seem right. To accelerate 107m/s in 10-5s requires an acceleration of 1012m/s2, which is about 1011g. Without doing more mathematics and probably writing a computer program I can't tell whether your claims are in the right ballpark.

IsaacKuo

2010-Oct-12, 07:33 PM

I was considering speeds more of the order of 0.1 to 1% c.
This is far too slow, in my opinion. It would take thousands of years to reach even nearby star systems at that speed. Even if it takes a thousand years to improve technology, later missions would arrive far sooner.

We don't know what the maximum practically attainable speed is,...
Like I said, I've explained out methods which would be useful for speeds greater than 60%c. The basic components and technology required for the techniques I favor all either exist or are near term technology. However, the sheer cost is something which we're far away from being able to deal with.

...or how far they need to travel. Their target might be a companion of their primary.
The context of the question is potential alien visitors to our star system. Therefore, the minimum travel distance would be over 4 light years. The target in question is our Sun, not a companion of an alien primary.

For general interstellar travel, the optimal speed might be lower than 10%c, depending on their objectives. For example, if the budget for launching interstellar vehicles is dominated by the energy, aliens could launch around 100 1% c craft for each 10%c craft.
I disagree. The amount of energy available should increase at least until the solar energy of the star is utilized. This provides an exceptionally high amount of power and energy. If you calculate out how much energy various potential interstellar missions would take, the requirements are on the order of hours or days of starlight power. A more plausible limitation is the relatively small number of target star systems within reasonable travel times. In other words, more speed is more important than conserving energy. A 2X increase in speed gives you access to about 8X as many target systems. Of course, this is only possible up to the speed of light limitation.

I've even considered how much energy cost would be involved for a massive overkill Earth-scale colonization mission. That is, sending a relativistic colony ship with a living area on the order of Earth's surface volume. IIRC, the energy cost would still only be about 2 weeks of Sunlight. I've come to the overall conclusion that energy isn't the limitation.

I'm sorry, but you must admit that big round numbers like "100 million" are not very believable.
Nonsense. I was giving an order of magnitude. When giving an order of magnitude, you're supposed to give a big round number.

That doesn't seem right. To accelerate 107m/s in 10-5s requires an acceleration of 1012m/s2, which is about 1011g. Without doing more mathematics and probably writing a computer program I can't tell whether your claims are in the right ballpark.
Heh. I made the same mistake twice--actually three times because I was confused by your statement. I thought--Huh? 1011 is 100 million. So? Of course, it's not 100 million, it's 100 billion. Oops.

In any case, the bottom line is that the Oberth effect isn't so easy to exploit for speeds greater than a thousand km/s or so. White dwarfs are as useful as neutron stars or black holes when it comes to the Oberth effect, and white dwarfs are far more commonplace.

Jeff Root

2010-Oct-16, 12:33 AM

dgavin

2010-Oct-17, 11:58 PM

Just from what has been said in this thread, I get the impression
that Phil might have been talking about the acceleration required
for an alien invasion force to reach Earth now if it left its home
planet several light-years away shortly after learning that Earth
has more-or-less intelligent life on it. That would require some
hefty acceleration if they learned about our existence from, say,
missile detection radar first used in the 1960s.

-- Jeff, in Minneapolis

I'm with you on this one. Phil was definately talking in context of a rocket being used, to accelerate a ship to speeds to that it could coast for most the journey, in reguards to the g-force problem.

IsaacKuo

2010-Oct-18, 01:37 AM

I'm with you on this one. Phil was definately talking in context of a rocket being used, to accelerate a ship to speeds to that it could coast for most the journey, in reguards to the g-force problem.
No, he wasn't. I watched the episode. He talked of accelerating at high accelerations for many years, which is simply wrong. Unless your destination is another galaxy, accelerating at high gees for many years will mean you have overshot your destination...and you're already in intergalactic space. If you have already overshot the target, then the question of coasting or not is moot!

dgavin

2010-Oct-18, 02:14 AM

No, he wasn't. I watched the episode. He talked of accelerating at high accelerations for many years, which is simply wrong. Unless your destination is another galaxy, accelerating at high gees for many years will mean you have overshot your destination...and you're already in intergalactic space. If you have already overshot the target, then the question of coasting or not is moot!

Yes, but that was after he talked about the lethal issues of g-forces from a push to speed/coast a while/decelerate rocket. He also stated on his own blog that he did not have the time to address this topic properly, as only 1 minute was slotted to it. So to try to explain that even a constant acceleration of 1G for a year is impossible because of relativity, is a bit beyond both the slotted time frame, and his intended audience.

Thats par for the course with science shows.

Van Rijn

2010-Oct-18, 03:13 AM

Yes, but that was after he talked about the lethal issues of g-forces from a push to speed/coast a while/decelerate rocket. He also stated on his own blog that he did not have the time to address this topic properly, as only 1 minute was slotted to it.

Whatever the reason for the problem, the statements, I'm afraid, just came out confusing and wrong. This was a case where it would have been better to avoid the statements entirely, if he didn't have time to say it right.

So to try to explain that even a constant acceleration of 1G for a year is impossible because of relativity, is a bit beyond both the slotted time frame, and his intended audience.

It is certainly possible, under relativity, for a ship to accelerate at 1G for a year.

Thats par for the course with science shows.

But this is the BA, who made a name pointing out mistakes. Mistakes happen, but I would hope, for the future, he would have folks looking over the script to catch things he might have missed (as everyone does), and hopefully be ready to redo things if they get too confusing.

R.A.F.

2010-Oct-18, 03:46 PM

He also stated on his own blog that he did not have the time to address this topic properly, as only 1 minute was slotted to it.

How much time was "slotted" for the F16 ride? That's the problem with doing shows like this...there is always the "need" to be entertaining and obviously it is not as much "fun" to watch Phil give a lengthy explanation as it is to watch him riding a jet.

At least that's my "take" on it.

grapes

2010-Oct-18, 06:04 PM

It is certainly possible, under relativity, for a ship to accelerate at 1G for a year.Depends.

If you mean, the crew experiences normal gravity, yes, under relativity. If you mean 10m/s/s in the universe frame, no, under relativity--that would push it over the speed of light. In context, it would appear that the second is meant, but then that would also mean that the crew would not experience normal gravity.

dgavin

2010-Oct-19, 01:37 AM

How much time was "slotted" for the F16 ride? That's the problem with doing shows like this...there is always the "need" to be entertaining and obviously it is not as much "fun" to watch Phil give a lengthy explanation as it is to watch him riding a jet.

At least that's my "take" on it.

Well said.

Not only that you have to also remember that what Phil wants to say (or does actually say), and what the script writers, direcotrs, editors, etc... actualy wind up putting in the final edit can be a problem too.

Even if (and thats a big if) the BA was on the final editing crew, he's also human and will make mistakes at times. Just because he is the BA is not a reason to hold him to a higher standard then others.

There is a lot that goes on with TV production that can cause errors or the like, and I think the BA should be given the benefit of the doubt here, is all i'm really trying to say.

grapes

2010-Oct-19, 02:13 AM

As I mentioned in the other thread, there is discussion on BA's blog. Here's BA's comment:

http://blogs.discovermagazine.com/badastronomy/2010/10/06/bad-universe-contest-winner-and-some-skepticism-for-free/#comment-315910Blog comment #20:
The idea of acceleration versus velocity was one I wrestled with. Of course, I understand all this! But conveying it to an audience who may not understand acceleration versus velocity gets very difficult, especially when I had about one minute to explain it. My new mantra!

IsaacKuo

2010-Oct-19, 02:52 AM

Well said.

Not only that you have to also remember that what Phil wants to say (or does actually say), and what the script writers, direcotrs, editors, etc... actualy wind up putting in the final edit can be a problem too.

Even if (and thats a big if) the BA was on the final editing crew, he's also human and will make mistakes at times. Just because he is the BA is not a reason to hold him to a higher standard then others.
I'm not holding him to a higher standard. Bluntly, he wasn't just a little bit wrong. He was completely wrong, and even worse than Hollywood space opera that doesn't even pretend to try (like Star Wars, or The Chronicles of Riddick, or whatever).

There is a lot that goes on with TV production that can cause errors or the like, and I think the BA should be given the benefit of the doubt here, is all i'm really trying to say.
I would agree that he should be given the benefit of the doubt--IF there were enough room for doubt here. But there isn't. It's not a case where he oversimplified things or explained something that was kinda sorta right but for the wrong reasons.

His point was completely and totally wrong, and he left viewers less informed about the subject than if they had simply been watching a different channel--like Jersey Shore on MTV, for example.

Van Rijn

2010-Oct-19, 04:53 AM

Depends.

If you mean, the crew experiences normal gravity, yes, under relativity.

Yes, a ship could constantly accelerate at 1G for a year under relativity. What external observers measure is a different issue. The context for this discussion is the BA's comments about what crew would experience in an accelerating spacecraft.

Van Rijn

2010-Oct-19, 05:23 AM

I would agree that he should be given the benefit of the doubt--IF there were enough room for doubt here. But there isn't. It's not a case where he oversimplified things or explained something that was kinda sorta right but for the wrong reasons.

I agree. If it stopped at the flight time to Mars argument, I'd argue for oversimplification, but when it moved on to acceleration and interstellar travel, it just was wrong.

Senor Molinero

2010-Nov-08, 12:17 AM

Oi, what if the aliens come from a 5g planet? They would have evolved under those conditions, so a high acceleration craft would be a doddle for them. When they got here they would be throwing busses around like superheroes.

shadmere

2010-Nov-08, 03:25 PM

cjameshuff

2010-Nov-08, 05:28 PM

I was dismayed at the acceleration explanation as well. At first I thought it might be a confused description of relativistic effects (for some reason assuming the ship must accelerate constantly in an outside frame), but that doesn't really fit...it was just confused and wrong. Limited time for explanation is not an excuse, it would have been better not to mention it at all than to give such a blatantly wrong explanation.

Another issue was their test of the survival of any living organisms. Their test was only valid for a single large impactor with no small debris, or for objects impacting the moon. Small meteorites impact the ground at terminal velocity, a few tens of m/s, not multiple km/s, and fresh falls have been observed to frost over due to their still-cold interiors, so atmospheric entry wouldn't necessarily cook microbes inside them. And they apparently only did a visual search for surviving bacteria, not making any attempt to culture any potentially surviving spores. And I don't think the possibility of Earth's surface being an adverse environment for an organism adapted for asteroids or Mars was ever mentioned...

Too much focus on whiz-bang flashiness and a disappointing lack of science. Not just a lack of detail, but a focus on explanations that were just plain wrong. It seemed designed around jet flights and hypervelocity guns, not around the subjects being discussed.

grant hutchison

2010-Nov-09, 01:44 PM

Too much focus on whiz-bang flashiness and a disappointing lack of science. Not just a lack of detail, but a focus on explanations that were just plain wrong. It seemed designed around jet flights and hypervelocity guns, not around the subjects being discussed.I have a rule of thumb which states that any television documentary in which the presenter takes a flight in a fighter plane isn't worth watching, unless it's actually about fighter planes.

Grant Hutchison

Strange

2010-Nov-09, 02:44 PM

I have a rule of thumb which states that any television documentary in which the presenter takes a flight in a fighter plane isn't worth watching, unless it's actually about fighter planes.

Grant Hutchison

Is that the documentary equivalent of "jumping the shark".

ronin

2010-Nov-09, 06:53 PM

The F-15 Considered one of the most successful air superiority fighters of modern times and the predecessor to the F-16.

http://en.wikipedia.org/wiki/McDonnell_Douglas_F-15_Eagle

F-16. ;)

And I think it's inexcusable. As Van Rijn noted, 1 gee is enough to get to the Andromeda Galaxy within a few decades of ship time. Human beings are capable of somehow surviving exposure to 1 gee for decades at a time; aliens might be able survive it also. Acceleration isn't the limitation.

Phil is guilty of bad astronomy--and yes, the physics of relativistic time dilation and the scales of time and distance in the universe are indeed astronomy.

He also missed out on the opportunity to discuss the real challenges involved in interstellar travel--things like the speed of light, the mind-numbing distances involved, the rocket equation, the heroic amounts of kinetic energy involved at relativistic speeds...

slang

2010-Nov-09, 10:19 PM

kamaz

2010-Nov-10, 06:13 PM

With Phil Plait loosing cred, I think it's time for someone else to carry the torch. BAUT: The movie.

djellison

2010-Nov-12, 10:36 PM

I have a rule of thumb which states that any television documentary in which the presenter takes a flight in a fighter plane isn't worth watching, unless it's actually about fighter planes.

Grant Hutchison

Pity - because 'Wonders of the Solar System' and 'James May on the Moon' were both superb, and arguably the best space themes scientific programming in the past decade.

grant hutchison

2010-Nov-12, 11:43 PM

Pity - because 'Wonders of the Solar System' and 'James May on the Moon' were both superb, and arguably the best space themes scientific programming in the past decade.I'm afraid I had Brian Cox in mind as a prime example of the rule in action.
And I had James May in mind when I allowed that documentaries which were actually about the plane could be worth watching: he made an entire documentary about the U2 flight that featured in On The Moon.

Grant Hutchison

JeffD1

2011-Jan-28, 04:45 AM

I haven't read the book, but a failure of knowledge, surely. The calculations are simply kinematics. Anyone with basic arithmetic can multiply a large acceleration, say, 2g, by a long time, say a month, and get an enormous velocity.hmmm, a month at 2 Gs?
ignoring Einstein momentarily....
1 month=30 days (approx)=2592000 seconds
v=at = 2 X 9.8m/s2 X 22592000 sec = 5.08E7 m/s = 17%c

Still going to take a loooong time to get to another star.

Now at say 6 Gs, close to the limit of human endurance over a short period, you get to c (oops! better invoke GR now)
However even AT c its going to be a couple dozen years round trip.(at least for those waiting here)

I have not seen the episode but perhaps Phil mentions that there will have to be a physics breakthrough that allows effective ftl travel before interstellar travel is feasible. If we can then invoke ftl travel we can certainly invoke other magical solutions to the accelerative forces on occupants of the ship.