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Imagine we have a faster-than-light drive which costs ~$250,000 USD per drive and can propel an ISS-sized craft at 1000 times the speed of light. It is reliable and has safeguards that stop it from plowing into things at high speed. How the FTL drive works is irrelevant; it could be an Alcubierre drive or powered by lalalaicanthearyouium.

The drive has its own included fuel/power supply which, for all intents and purposes, is infinite. (eg: unlimited or easily replenish-able, etc.) Additionally, this universe has no FTL communications other than mail carriers fitted with FTL drives.

Would there still be any value in building and operating (optical/radio/whatever) telescopes for (e.g.) locating exoplanets, studying stars, etc.?

Would telescopes be gradually retired and replaced by exploration ships?

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Without telescopes, how do you know where to go? – iAdjunct Feb 13 at 15:12
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Telescopes let you see the past; FTL lets you visit the future. – iAdjunct Feb 13 at 15:14
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Note that with FTL, you can watch the same event over and over again now that you know where to look. – Richard Feb 13 at 22:14
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Not only that, @Richard, you could collect thousands of years of data in a relatively short time by alternately hopping forward and taking images. You could watch a supernova unfold into a stellar nursery (assuming that is actually what happens) within a human lifetime! You just have to put the telescope ON the FTL ship. – starrise Feb 14 at 0:07
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I've thought it would be a fun idea in a future where we have FTL to travel a couple thousand light-years out and point a telescope back at Earth in order to watch the events of history unfold live from a birds-eye view. I think telescopes would become more useful with FTL. – Slipp D. Thompson Feb 14 at 13:35

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1000 times the speed of light means you can visit something 500 lightyears away in a one-year round trip. 5000 lightyears would take a decade and you are still not even leaving our galaxy. In contrast some things that can be observed with telescopes are millions or even billions of light years away. So astronomy would still need telescopes!

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This is correct. Fast FTL is great for zipping around the galaxy, but telescopes even now are looking at far away galaxies, or even towards the edge of the universe (which is really a means of saying looking back to the beginning of time). In some ways an FTL drive allows you to use a telescope to look at things at any point in time. Want to see what the sun looked like 2000 years ago? Use your 1000c FTL drive for 2 years, stop, turn around and point your telescope at the sun. – Scott Whitlock Feb 13 at 22:35
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This is actually incorrect. Thanks to the wonders of relativity, an FTL ship that left earth, visited (say) M31, then turned around came back, would actually arrive before it left. If there were any people on that ship, eons would have passed for them--but for us here on earth, it would appear faster than instant. physics.stackexchange.com/a/54242/48740 – Jerry Coffin Feb 14 at 15:54
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I would think that any FTL drive would render relativity laws as the stand obsolete. – Keith L Feb 14 at 16:43
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@KeithL Well, that still leaves you to explain how come relativity seems to work perfectly, except that the inherent "speed limit" is removed. Relativity isn't just a neat mathematical trick - it also works, and is responsible for a huge amount of stuff everywhere around you. The usual solution (other than handwaving) is in the form of "Relativity, FTL, causality - pick any two". Jerry's comment throws out causality, which might be perfectly fine in our universe; yours wants to throw out relativity, while keeping all the things predicted (and solved) by relativity. That's... tricky. – Luaan Feb 15 at 9:05
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I guess that since the premise here violates everything we know about the laws of nature, you're free to make up your own rules about what happens in the fantasy world where this is possible. – Max Williams Feb 15 at 9:10

Yes and no.

It'd be worth keeping some of the larger telescopes around, simply because they have a wider area of coverage. A large radio telescope can cover a significant portion of its sky and listen for incoming signals from that zone. This is an advantage, because you then don't have to send an exploration ship out to every possible area that the telescope would have covered to get the same information.

However, for more detailed explorations of a target identified as interesting by the telescopes, exploration ships would be incredibly useful - you can get to the target in no time flat, get some good images of it, and get back home again in the same no time flat.

Essentially, the two would work together. The telescopes have a wide area but little detail; the ships have a narrow area but lots of detail. It's a perfect complement. Things like SETI and the search for other habitable planets would become easier by orders of magnitude.

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But 1,000 times the speed of light is useless for close-up examination of the things that are seen by large telescopes, which are typically many millions of light years away and so would need many thousands of years of travel time. It would be great for studying common things like exoplanets and typical stars, but no good for anything else. Even the centre of our own galaxy would be a sixty year round-trip. – Mike Scott Feb 14 at 8:05
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Actually, a radio telescope only listens to a tiny portion of the sky at any one time (ignoring offset feeds and such). Radio telescopes are built the way they are because it is quite easy in UHF and up to get high gain with parabolic reflectors, which means you can listen to very weak signals (remember that EM signal strength falls with the square of the distance). However, because that energy must come from somewhere, as you increase gain (build bigger dishes) for a given frequency, the reception angle becomes smaller, requiring more accurate aiming. Compare aiming a home TV satellite dish. – Michael Kjörling Feb 14 at 12:21
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@MichaelKjörling Yes, but in relative terms compared to an exploration ship, they're looking at far more. – ArtOfCode Feb 14 at 12:47

Fly telescopes faster than light, then point them toward the Earth. Now you can see the past. Any time in the past.

I don`t think we could get the resolution to solve crimes and disambiguate historical events of humans on the ground, but I suppose the detailed formation of the Solar System would give up its mysteries pretty fast.

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You'd have to get farther and farther away to see further and further into the Solar System's past. Eventually - and I would think quite quickly - you get to a distance where you can't detect anything meaningful. – HDE 226868 Feb 13 at 19:43
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Not to mention, it would take 4.5 million years each way. There are probably better ways to figure out how the earth formed. – Daniel M. Feb 14 at 0:37
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@HDE226868 I was thinking that too, but then I got to thinking somebody would probably invent some kind of FTL telescope that works by travelling somewhat perpendicular to the object being observed so as to intercept the same moment (light emitted as the same time) from a number of different locations, sort of like a trans-luminal interferometry. – Michael Feb 14 at 20:29

We'd have a lot more telescopes, because they would be much more useful, and they'd be fitted with FTL drives. Just for example, imagine a fleet of telescopes searching for a visual signature associated with the recent gravitational wave detection. Just going there wouldn't be possible, because we don't know where it is and it would still take over a million years at 1,000 times the speed of light, but we could move steadily further from Earth and examine different parts of the sky at the exact instant.

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Very Destiny! – Lightness Races in Orbit Feb 13 at 20:42

Well I'm surprised no one has provided the most obvious answer yet:

No, we would still need telescopes because you may want to look at something while not actually being there, such as a dangerous, uninhabitable planet or even looking at stars.

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Or to have a look at what's there before deciding to go there. You don't travel on vacation without taking a look at the brochure beforehand :) - Or more specifically: With about 1e8 stars in our galaxy alone, which should you head to? – JimmyB Feb 15 at 10:57
    
That is really an annoying statement : Well I'm surprised no one has provided the most obvious answer yet – Vincent Feb 27 at 20:24

Not quite.

Plusses of faster-than-light travel for astronomy:

  • You can see events happening in the present. Astronomers can only observe objects in the past. Even our observations of the closest star system Alpha Centauri, are four years out of date. Sometimes, the finite speed of light really sucks. But with faster-than-light travel, you can get to the stars and then transmit the information back to astronomers on Earth very quickly.
  • We can actually get up close and personal with astronomical objects. Earth-like exoplanets are hard to detect because they're hard to find from so far away. But traveling to another star system would make confirming detection easy. Like the first point, any space travel has these plusses, but only faster-than-light travel makes it really feasible for astronomers on Earth.
  • It's cool, and will get funding. Seriously, it's going to be much easier to convince people, companies, and governments to fund a faster-than-light starship than the convince them to fund a telescope. Telescopes are really cool, but, to most people, spaceships that can outrun a photon are cooler. So astronomers will get a lot more money, I would predict.
  • There's no atmosphere or Sun to block observations. This is a problem for astronomers on Earth, which is why space telescopes are so popular. Sure, the central star in a system would still make observations tricky. But there's plenty of places a faster-than-light ship could go to mitigate this, assuming adequate fuel and piloting ability.

Plusses of still using telescopes:

  • Observing via different wavelengths is easy. The Hubble Space Telescope is pretty much the number one source of visible and near-infrared images of astronomical objects. A lot of other images we get from telescopes are false color. You'll need to drag a telescope along on your ship anyway to properly detect objects in these wavelengths. In some cases, this is easy. But try dragging the Very Large Array or Arecibo Observatory on a trek across the stars. Logistically, it's hard to bring along something that big in a single spacecraft.

    Sure, you could try to put a bunch of radio telescopes in an array in space. eLISA will hopefully do that to search for gravitational waves. But eLISA involves only three different spacecraft. Coordination is relatively easy, and they'll be staying in a heliocentric orbit. Putting the 27 25-meter-wide telescopes of the VLA in space and then bringing them hundreds or thousands of light-years away is monumentally difficult.

  • They're (generally) not too complicated to use. These faster-than-light ships are apparently pretty cheap, but given that there's no faster-than-light communication besides using these ships, you either need a human crew (difficult) or an autonomous probe (a terrible idea, given that encounters with aliens would not go well, and I don't think people would trust it enough in those cases). Telescopes on or orbiting Earth are much better.

So no, these faster-than-light ships would not entirely replace telescopes immediately. You'd see a balance between the two, with radio telescopes being gradually phased out if (and only if) radio arrays were feasibly on these spacecraft. Eventually, you'd see only a few telescopes left on Earth or in Earth orbit. But I'd bet you anything that they'd be probing the sky for radio waves.

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I would a think a very large array is especially easy to deploy in space. No? – Samuel Feb 13 at 17:56
    
@Samuel I would disagree, because it would be difficult to keep that many telescopes perfectly aligned, especially after traveling hundreds or thousands of light-years to some other star system. Arrays on Earth are simple enough because they don't really move. In space, that's going to be different. It can be done with fewer telescopes, but with something the size of the VLA, that may be much harder. – HDE 226868 Feb 13 at 17:57
    
@Samuel Edited, by the way. – HDE 226868 Feb 13 at 18:08
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Telescope swarms would be less difficult than existing Earth-based drone swarms. Fly them out there, let them go, and they'll position themselves relative to each other. The size is not much of a problem in zero-gravity. – Samuel Feb 13 at 18:17
    
@Samuel I think it would still be much simpler and cheaper to just keep the telescopes on Earth. – HDE 226868 Feb 13 at 18:21

Sometimes people won't want to wait. Even at 1000c, the are only about five hundred systems you can go to and back in a month. Telescopes are still needed to observe systems farther away than that.

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Hi WGroleau and welcome to Worldbuilding.SE Can you elaborate your answer a bit more? Why do I need telescope for farther systems? I could just travel two months for example. (I know why, I read it in the other answers. Just want to point out where in my opinion your answer is lacking) – J_F_B_M Feb 14 at 1:40
    
WhenI posted this, I did not see any other addressing this factor. Now that two others have done so in more detail, I see no point in me repeating them. – WGroleau Feb 21 at 16:23

There would be still things that could not be done with FTL:

  • By using telescopes you observe the stars as they were when the light was emitted. Exploratory ships would see the star systems as they are at their moment of time.
  • Powerful telescopes allow observations of very distant objects. If building them on the opposite site of the Milky Way were possible it would be a much more tempting opportunity to use it for instance for studying nearby galaxy clusters, motion of galaxies in Laniakea (our) supercluster etc. Even if you had FTL capable of visiting e.g. Andromeda galaxy there would always be a lot of objects too distant to visit.
  • The two above connected give us one more opportunity completely unavailable for pure FTL based exploration: research of the past evolution of universe. By observing very distant galaxies we in fact observe what our universe has looked like in distant history. In fact observing background radiation is observing the moment just after big bang.

Nevertheless FTL based exploration would shift science interest of telescope operators to new fields. I would expect them to be more interested in studying nearby galaxies and galaxy clusters (as it would be easier if you could build a network of telescopes located on every arm of Milky Way). It may be also tempting to look for exoplanets in nearby galaxies (like Magellanic Clouds) or deep in core of Milky Way (assuming the telescope technology developed enough).

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I think the history point is really important: if you want to study the Cosmic Microwave Background, you can't just walk over to the moment of photon decoupling, when the universe was aged approx 378k years, take your measurements, and walk back. Even if your FTL drive is also a time machine (because of relativity or otherwise) that's not a simple journey at 1000c. – Steve Jessop Feb 15 at 15:02

The greatest reason for keeping telescopes is because it's "inconvenient" if one's FTL-craft barges into a star. Or a planet. Or even an analogue to a dense asteroid field.

Until space is well-mapped, the only really safe way to FTL-it around the galaxy is to do what could be called "Nano-Jumps:" "Tiny" hops, (1-2 light-years, max.) followed by Loooong periods of looking very hard, [with telescopes!] to see if said stars/planets/asteroid fields/et. al. could be apt to get in the way.

I'd estimate that your FTL would need a series of "clean" corridors with a radius of at least an AU, each, to permit unrestrained, full-power, FTL flights to "mapped" destinations. And then, these "corridors" should be thoroughly re-examined at least every few decades, to be certain that wandering mass-bodies shall not endanger travel.

This would take quite a long time to establish such a network, and quite an active FTL fleet to maintain same.

Otherwise, there would be significant "attrition" among your home-world's FTL fleet, as leadfooted pilots turned stars into novas by trying to fly through 'em.

What's the danger? Look at our trans-Plutonian "hive" of dwarf planets (potentially, in the dozens, if not hundreds); then add in a smattering of wandering post-nova planetary bodies, proto-stars, rogue brown and black dwarves, plus "ordinary" stars and planets, as to what one's FTL might vaporize.

Very short hops, coupled with very long looks, happens to be the only way to be even remotely safe. At least until ones' "trade routes" are well-mapped.

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You could use telescopes with FTL not to come closer to observer objects, but farther away (to the past). So ie when we detected exploding star, you can fly away from it and observe preconditions in great detail.

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Obsolete? Surely not.

Does the existence of airplanes make telephones obsolete? Why should I call someone on the phone when I could just get on an airplane and fly to see him?

The obvious answer is, Because, even though airplanes are fast, they still take time to get there, much more time than it takes to call someone on the phone.

Even at 1000 times the speed of light, reaching a destination 1000 light years away -- what's that, 1% of the distance across the galaxy? -- would take a year.

Even if I wanted to study someplace close in cosmic terms, it's likely that a space flight would require non-trivial amounts of time. Consider air travel on Earth: Even if the flight itself took zero time, just the time it takes to drive to the airport, go through security, wait for the plane to arrive, get everybody on board, etc etc takes hours. For trips of a few hundred miles you spend more time on all these peripheral things than actually in the air.

Of course you could pile on more assumptions: Starships are so cheap that everyone can afford one, and you can launch it from your backyard so all you have to do is walk out and hop in. Controls and navigation are so simple any child can fly one. They never need to be refueled and they require no maintenance. They are 100% safe. Etc.

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Turning an FTL drive into a time travel machine is a simple high-school relativity problem.

So your FTL system supports time travel, causing a technological singularity (the ability to send information backwards in time). Predicting what happens after a singularity is difficult.

But, as time travel is invented at every time, we are already after the invention of time travel (if it is ever invented), and we use telescopes. So no, FTL does not mean that telescopes are never used.

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