RichS's answer to the question "Why couldn't Ellie's experience be corroborated?" states in no uncertain terms that the alien signal couldn't have been faked due to the way that radio telescopes are able to discriminate distant objects using parallax.

"You can put a satellite in orbit around Earth and make your satellite transmit a signal, and pretend the signal is from Vega. A radio dish could pick up the signal when your satellite is in the same position in the sky as Vega. All a radio astronomer has to do is ask a technician at a different radio telescope a few thousand miles away to point their dish at Vega. When the other dish points at Vega, it won't be pointing at your satellite, so it won't get the fake message from your satellite."

So why, if there are known techniques for detecting the origin of an extra-solar signal, did certain characters in the film (and the book) feel that Hadden could have been tricking them? Surely the science is airtight?

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    Some people just can't accept the truth. Irrationally always trumps rational thought. Just ask anyone trying to convince a climate change denier that we are truly undergoing human-caused climate change.
    – iMerchant
    Commented Mar 5, 2017 at 20:49
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    @iMerchant - Occam's razor. Is it more likely to be a hoax or aliens?
    – Valorum
    Commented Mar 5, 2017 at 20:52
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    @iMerchant - Ah, but just try to convince a climate change believer that the changes in climate might be a good thing and you'll face the same difficulties :-)
    – Valorum
    Commented Mar 5, 2017 at 20:53
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    I'd say it depends on how strong one's beliefs are and how irrational they are
    – iMerchant
    Commented Mar 5, 2017 at 20:53
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    Because it's easier to be political than be real? And since it is possible, if you're cleverer, richer, and stranger than the rest of the world, to arrange multiple satellites to cover multiple angles. Yes, that sounds stupid, but apparently that might be more plausible than aliens with a good will message and wormhole generators..
    – Radhil
    Commented Mar 5, 2017 at 20:55

2 Answers 2


I can't speak to the film. But in the book, the idea that the signal was broadcast by a satellite in "some orbit that looks like sidereal motion" was presented by Kitz, who simply didn't know or care whether that made sense. It wasn't even the main part of his argument, just an offhand speculation.

Kitz pressed on, making sparkling new patterns of facts assemble themselves in the air before her, rewriting whole years of her life. She hadn't thought Kitz dumb, but she hadn't imagined him this inventive either. Perhaps he had received help. But the emotional propulsion for this fantasy came from Kitz.

This wasn't a discussion, or an attempt to discover the truth. Even if Ellie had an opportunity to point out the parallax issue, he'd have dismissed it as irrelevant, found some other excuse. (She might have done so instead of arguing that the content of the signal couldn't have been faked, but under the circumstances, it is understandable that she would focus on that aspect. It wouldn't have made any difference; he wasn't willing to consider any evidence, no matter how strong, that conflicted with his idea of the world the way he wanted it to be.)

You should also note that the general public were not told that the signal was faked, they were told that the Machine had failed to work. Kitz simply never had to defend his theory in front of anyone who might understand how implausible it was, or for that matter, in front of anyone who was willing to face up to the possibility that Ellie's story might be true.

To be fair to Kitz, it is very difficult to rigorously prove that any phenomena isn't a hoax, particularly after it is all over and all you have to go on is the records. There's no indication that I'm aware of that any of the scientists took any steps to check for intentional deception, and it seems entirely plausible that they wouldn't; scientists don't tend to think that way. That makes the hoax theory implausible but not necessarily impossible, or as Ellie puts it (chapter 5):

The Argus telescopes, working together with radio observatories in West Virginia and Australia, has determined that the source was moving with Vega. Not only was the signal coming, as carefully as they could measure, from where Vega was in the sky; but the signal also shared the peculiar and characteristic motions of Vega. Unless this was a hoax of heroic proportions, the source of the prime number pulses was indeed in the Vega system.

You'd probably have to start with a spacecraft at a considerable distance from Earth, far enough that the parallax difference and the difference between a straight-line course and freefall couldn't be distinguished by coarse instruments. That would be very expensive, would take a very long time, and doing it surreptitiously might well be beyond the capabilities of 1980s technology altogether. Then you'd need to compromise perhaps a hundred radio telescopes and radio telescope arrays, either with the help of collaborators or more surreptitiously. In my amateur opinion, even if you could get this off the ground you'd almost certainly get caught sooner or later, but as they say, absence of evidence isn't evidence of absence.

Also, as Kitz points out (abridged):

"The Message stopped the moment we activated the Machine. The moment the bezels reached cruising speed. To the second. All over the world. The Message stopped in mid-bit. Now that was really foolish of you."

It has been suggested that the idea that Pi could have been engineered to contain a message is unreasonable, and by the standards of hard science-fiction that's certainly true; but any violation of causality is just as hard to swallow for the usual reasons - as soon as you can travel through time you can create paradoxes. Given the choice between the implausibility of a successful conspiracy to fake the message and the implausibility of time travel, if I was presented with this scenario in real life I'd be awfully tempted to decide in favour of the conspiracy, no matter how unlikely it sounds.

I speculated in the comments that it might even be possible to compromise the dishes remotely, by beaming a signal directly at each dish and modulating it as the dish moves. On second thoughts, I don't think you'd be able to measure the movement of the dish accurately enough from a distance to make this convincing. But if you've bugged the dish's control systems, and are able to intercept and replace the signal coming from the dish before it is processed, you might be able to make it work without collaboration by station staff.

My main doubt is whether they'd have had sufficient computing power in the 80s to pull this off, particularly if it was necessary for the equipment to be hidden or disguised. But no doubt Kitz would argue that Hadden had developed the necessary technology in secret, or that it was top-secret Russian equipment, or whatever. It can't be shown to be physically impossible, or at least, not to an amateur, so again, all that Ellie could argue is that it would be implausible. That might convince someone who was willing to be convinced. But it would never convince Kitz.

A few supporting quotes, added as I work my way through the book.

From chapter 5:

Television camera crews in fixed-wing air taxis and chartered helicopters began making low passes over the facility, sometimes generating strong radio interference easily detected by the telescopes. Some reporters stalked the officials from Washington when they returned to their motels at night. A few of the more enterprising had attempted to enter the facility unobserved - by beach buggy, motorcycle, and in one case on horseback. She had been forced to inquire about bulk rates on cyclone fencing.

This establishes that this one site, at least, wasn't particularly secure against possible intruders, even amateur ones. Professional spies would get in no trouble. Whether that was representative of the real world at the time Contact was written, I don't know, but if it was in fact a case of artistic license, it doesn't seem an unreasonable one.

From chapter 8, slightly abridged:

"There's also the question of personnel," Vaygay continued. "There are at most a few hundred really capable radio astronomers in the world."

This establishes that the number of people involved in Kitz's hypothetical conspiracy would not need to be excessively large. (For a real world analogy, consider the tobacco industry's suppression of evidence of the health risks of smoking. There were presumably at least several hundred people aware of this at the time, but it didn't become public knowledge until much later.)

From chapter 10, abridged:

Joss had insisted that the discussion be held here, at the Bible Science Research Institute and Museum in Modesto, California. Just outside was a plaster impression from a Red River sandstone of dinosaur footprints interspersed with those of a pedestrian in sandals, proving, so the caption said, that Men and Dinosaur were contemporaries. The conclusion drawn in the caption was that evolution was a fraud. The opinion of many paleontologists - that the sandstone was the fraud - remained, Ellie had noted earlier, unmentioned.

The main purpose of this chapter is to introduce the question of how God might make His existence unmistakable to the modern world, but I think it also serves as a foreshadowing of Kitz's later antagonism, establishing that many people really do consider scientists as a group to be inherently untrustworthy, just the sort of people that might be willing to conspire to fake a set of alien signals.

... and a final two quotes to finish off with. The first is from chapter 14, when the President is looking at Vega through a telescope:

"What if there was no turbulence, Ken? What would I see then?"

"Then it would be just like Space Telescope above the Earth's atmosphere. You'd see a steady, unflickering point of light."

"Just the star? Just Vega? No planets, no rings, no laser battle stations?"

"No, Ms. President. All that would be much too small and faint to see even with a very big telescope."

"Well, I hope your scientists know what they're doing," she said in a near whispher. "We're making an awful lot of commitments on something we've never seen."

Der Heer was a little taken aback. "But we've seen thirty-one thousand pages of text - pictures, words, plus a huge primer."

"In my book, that's not the same as seeing it. It's a little too ... inferential. Don't tell me about scientists all over the world getting the same data. I know all that. And don't tell me about how clear and unambiguous the blueprints for the Machine are. I know that too. And if we back out, someone else is sure to build the Machine. I know all those things. But I'm still nervous."

Here, we have more foreshadowing, as we see a mostly sympathetic non-scientist character still struggling to accept indirect evidence (such as parallax) as proof.

I'll let Kitz have the final word:

"We're not unreasonable," Kitz had finally said in agreeing to the compromise. "You come back with a solid piece of evidence, something really convincing, and we'll join you in making the announcement. We'll say we asked you to keep the story quiet until we could be absolutely sure. Within reason, we'll support any research you want to do. If we announce the story now, though, there'll be an initial wave of enthusiasm and then the skeptics will start carping."

  • You may wish to add that Ellie herself (earlier in the book) admits that it might somehow be a hoax
    – Valorum
    Commented Mar 8, 2017 at 9:19
  • Thanks. I'll have to dig into the book again to find the quote, though. Maybe this weekend. Realistically, it could be some sort of hoax. You'd have to have collaborators at every radio dish, or compromise them in some other way, so it seems pretty darned implausible. But not logically impossible. Commented Mar 8, 2017 at 20:15
  • (I suspect that a beamed transmission aimed directly at a radio dish, and modulated in real-time as the dish moves, could in fact fake the parallax. You'd almost certainly be able to detect such an attack, but only if you thought to look for it. There's a quote I can't place at the moment, about scientists being used to fighting a universe that played fair, and easily fooled when faced with a conman who isn't. In the context of paranormal studies, I think.) Commented Mar 8, 2017 at 20:21
  • @HarryJohnston Aiming the transmission directly at the dish won't fake parallax. It's simple to check. All you do is ask somebody at a different radio dish thousands of miles away to point their dish at Vega. If they get the same signal, then you know it's from Vega. If they don't get the signal, you know it has a terrestrial origin.
    – RichS
    Commented Mar 11, 2017 at 22:40
  • @RichS: the point is that other dish would also be compromised, one way or another. There's only a finite number of them, after all. Any conspirator worth his salt would have made sure he had them all covered before attempting the fraud. Commented Mar 11, 2017 at 22:45

The answer is that there is no good answer to this question.

The author of the book, Carl Sagan, was a very smart man with a lot of knowledge of radio astronomy - or more to the point, radio astrometry. (Astrometry is the branch of astronomy related to measuring the positions and motions of stars and other celestial objects.) When you're talking about parallax, you're dealing with astrometry rather than other branches of astronomy.

Before I continue, I want to point out that I really admire and respect Carl Sagan. He inspired my interest in science. His dedication to rigorously using the scientific method and exposing fallacies and superstitious nonsense helped raise the conversation about science and skepticism worldwide. Several of his books, The Demon Haunted World, Pale Blue Dot, Cosmos, and The Dragons of Eden show his deep commitment to skepticism and rigorous thinking.

As somebody who published science articles on radio astronomy research, he was likely aware of using a simple parallax test to distinguish interstellar radio sources from terrestrial interference. And that the same simple parallax test could also separate signals from Earth orbit from those from other planets in our Solar System. And parallax could also separate signals from within our Solar System from those outside it.

Since Sagan was writing a science fiction novel that was meant to be scientifically rigorous and since he was probably aware of basic techniques for simple signal confirmation, there is no excuse for any discussion in the book of the signal being a hoax. To those who have done radio astronomy, the use of a Hadden driven hoax as a possible explanation for the origin of the signal is as blatantly wrong as any discussion of a person hiding messages deep inside Pi.

Perhaps he did it for a non-science minded audience who could better relate to ideas about hoaxes than they could rigorously prove such a hoax was impossible.

For those of us familiar with Sagan and who are also familiar with the basic protocols among astronomers, it is disheartening to see this in his book. When he first published Contact, I remember conversations among other astronomers about what was wrong with the book. We talked about how it is impossible to modify the digits of Pi to hide a message. Not even God can change the digits of Pi. We also saw the subtler errors in the book that lay people probably missed.

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    Clearly some of the characters felt differently. This question was asking why they might think that.
    – Valorum
    Commented Mar 5, 2017 at 22:52
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    And the title of this post is "Why weren't they able to use parallax to corroborate Ellie's story?", not "Why do some characters in Contact believe the signal is a hoax despite evidence?" If that is what you really want to ask, please modify the original question and its title. :-)
    – RichS
    Commented Mar 6, 2017 at 0:24
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    The whole point of the "digits of Pi" thing was that it is impossible - for a person. (The claim that "not even God" can do it is unfalsifiable and hence meaningless IMO.) Commented Mar 7, 2017 at 23:50
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    I don't see why I should be restricted to an arbitrary list, but Formalism appears to meet the necessary criteria. Probably most anything but Platonism, really. Perhaps even that; I don't know whether Plato thought mathematical truths were prior to divinity or not. (I really don't know why you're getting so wound up about this; does it really matter to you that much whether Mathematics came before or after God?) Commented Mar 8, 2017 at 2:24
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    [Minor quibble, mentioned only because it means that I might be misunderstanding you: the premise of the story as I understood it is not that Pi is changeable or that it was modified, but that the laws of mathematics were designed in such a way that it had always and would always contain a message.] Commented Mar 8, 2017 at 2:39

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