Can we explore this universe

  1. Please ignore my question if you mock over stupid questions...

    Keeping in mind:
    1) The distance traveled by light in one year is one light year
    2) Material objects can not attain the speed of light
    3) Solar system is VAST, but at the same time it may be smaller than even a single star far far away from us. Imagine the size of that star system, and then the distance between solar system and that star system (simply billions of billions of billions of light years from us.)

    Now the question is :
    Can we happen to know what is out there in those systems (with todays technology we can't).
    But as stated earliier; it is impossible for a material object to attain the speed of light, so does that mean we can never have the technology to overcome this constraint.

    Is it the limit...?
  2. jcsd
  3. Ryan_m_b

    Staff: Mentor

    To accelerate to the speed of light would require either infinite energy or infinite time so yes, it is the limit. There are speculative proposals to get around this; wormholes and warp drives.

    It may be possible to create traversable wormholes to allow short cuts in space. However this requires exotic matter that may not even exist and you would still have to drag one of the wormholes to your destination of choice slower than light (you also have the tricky problem that you have now created a potential time machine but this could be resolved if Visser collapse or some other CPC held true).

    On the subject of warp drives this paper which is further discussed in this paper proposes ways of getting around the horrendous energy requirements outlined in this paper. The "trick" is to change the warp bubble so that it's exterior radius is microscopic yet the interior radius is large enough to accommodate your vehicle (essentially making a warp bubble that's bigger on the inside than on the out). Apparently this would greatly shrink the amount of energy needed to manageable levels. They don't outline how exactly a shell could be build around a ship in such a fashion nor how the ship could leave.

    However neither of these approaches fixes the other problems of a warp bubble such as requiring the construction of an exotic matter shell, superluminal signalling to steer/control the bubble and the huge amount of radiation a warp drive subjects you to. There are some interesting (but technical) objections in this paper that apparently show that a warp drive would only be capable of very low velocities as well as highlighting other problems.

    So without exotic matter that may not even exist we are stuck to trying to make slower than light vehicles. To make an interstellar vehicle would be fantastically complex though requiring horrific amounts of energy (even if we used an antimatter rocket we would need potentially thousands-millions of tonnes for a high fraction of c.) as well as a thorough understanding of ecology so as to make a stable environment in a closed system to keep the occupants alive.
    Last edited: Jul 18, 2011
  4. If we build ever bigger and stronger telescopes, we can explore the universe just fine without going anywhere.

    Yes, the distance between stars makes exploration through transportation difficult.. but not impossible. The less massive a particle, the easier it is to accelerate. We as a human species routinely accelerate objects to 99.9999% the speed of light in particle accelerators. I think the future of space exploration is accelerating intelligent microscopic probes close to the speed of light.
  5. Ryan_m_b

    Staff: Mentor

    To add to what chrisbaird has said we could build a network of telescopes arranged in a sphere multiple AUs wide to create an array of fantastic resolution (as described in this thread) and/or develop the technology to make beam powered starwisp probes.
  6. sophiecentaur

    sophiecentaur 14,717
    Science Advisor
    Gold Member

    There is, however, a limit to the distance you can 'see' light from. This is because the Universe is expanding and the recession of distant objects causes their light to get 'red shifted' so that its wavelength increases. This red shift eventually turns light into radio waves of increasingly long wavelength and eventually makes them undetectable - so you just couldn't detect things beyond this 'horizon' where the recession speed approaches c (and this c speed IS allowed because it's not objects travelling at c - it's just the space between that is expanding).

    I am never very convinced about discussions of wormholes etc., as a way of 'getting about' at FTL speeds. Whilst you could perhaps shove a few particles through a wormhole (if you could just find one) but just imagine how disruptive that could be on a living organism. The distortion to a body in the region of a black hole would be pretty fatal so this wormhole would, I think, need to be very big (millions of km across) so that you could go down the middle and be nowhere near the sides.
  7. Ryan_m_b

    Staff: Mentor

    I'm always sceptical about the horrendous energy requirements, need for exotic matter etc especially since it cost a significant fraction of the worlds richest nation just to put a few canned monkeys on the moon...
  8. Despite being limited by the speed of light, you could still theoretically get across the entire universe and back in a lifetime while undergoing an acceleration of g or not that much greater. This is because if you're going close enough to the speed of light, relativity causes distances to shrink.

    The problem with this is, of course, accelerating at g for decades is, right now, impossible. Perhaps eventually some technology will be developed that allows this, but it will most likely have to rely on some outside power/ mass source.

    The other problem is that if you actually did go across the universe and back, the same relativity that shortens your distances also insures that most likely the earth (and possibly sun/ universe) would not be here anymore.
  9. I have long pondered this question. I thought about it from the standpoint of a large array of ion drives. Let's say you get enough drives on the back of a ship to produce a .5 g acceleration, and a large fission plant to power all those ion drives. You constant boost ship could reach an external viewed speed of maybe .01 C. But what happens on the ship is the question, how much time dilation, the ions and now a lot heaver, and may continue to produce equal thrust. If ion drives can be improved to get to .9 c, then the ships time could dilate enough to pass the speed of light from the people on the ships point of view. A trip to a star 100 light years away might be just 10 years ships time. The down side is earth would age almost 150 years in such a trip.
    The first step would be a probe launched perpendicular to earth's southern orbital plane.
    The probe would have imaging equipment and a data link laser. The protocol could be any di-phase, manchester2 comes to mind. Observatories in the dry valleys of Antarctica could monitor it's speed by the cell sizes of it's clocked data stream.
    the data itself could be images the prob sees, and radiation levels at speed.
    might be a good place to start.
  10. sophiecentaur

    sophiecentaur 14,717
    Science Advisor
    Gold Member

    But that doesn't solve the problem of how much energy you need and how much mass you need to eject in order to produce the motive force (even with ion drives). Even a Fusion plant has limits to its energy capacity, too.
    The sums give you extremely big numbers for energy requirement, you know, because, in the end, you are approaching E = mcsquared.
  11. Ryan_m_b

    Staff: Mentor

    Taking antimatter rockets as having the highest Isp (1megasecond) to get to 99% of the speed of light would take 30 parts fuel to every 1 part ship! Bearing in mind you are still going to need a ship of such huge complexity so as to hold a stable ecology and industrial base that could mean millions of tonnes of antimatter. That's a ridiculous amount of energy.
  12. With even a short discussion of the Pros, we learn a lot more than weeks of lectures.
  13. I admit there are quite a few unanswered questions.
    Given a fixed power supply and ION drives, the ship should make an asymptotic approach to it's maximum outside observed speed. I was thinking around 30 km/sec. .01c.
    From the point of view of the ship, nothing has changed,(maybe a slight doppler shift.)
    It would be difficult to go faster the the ions being ejected.
    The experiment would come in after the ship hits is maximum outside speed.
    How much does time slow down?
    based on outside time am I throwing more ions out per second than I was before?
    Do those ions have a greater mass, and thus greater thrust?
    On earth, is my self clocking data stream showing a broader clock frame?
    We think we know some of the answers, but some will wait until we experiment.
  14. Ryan_m_b

    Staff: Mentor

    You can use an online calculator to figure out time dilation. Ion drives obviously need fuel, the limit to how long they can accelerate is determined by the quality of the engineering (keeping an engine going for years takes some good technology) and the amount of fuel available. From the view of the person on the ship nothing changes on the ship, the drive will operate at the same rate as normal. It will appear slower from someone on Earth however.
  15. I may be wrong or interpreted it wrong but this is what I think.
    In your frame of reference and that of the ions, nothing has changed in mass. The ions have the same mass as always and are providing the same thrust.
    In the frame of reference of someone on Earth, the ions have increased in mass, but so has the ship so acceleration will be unchanged.
  16. Ryan_m_b

    Staff: Mentor

    Emphasis mine. You are nearly correct but as I understand it from Earth they would see your acceleration slowed down because everything is slowed down. For me on the ship I may still observe myself accelerating at 10mps2 but for you on Earth I appear to be accelerating at 5mps2 because time dilation means that every minute for me is two for you.

    So acceleration doesn't change for the ship but because of time dilation you acceleration is perceived to be slower from an observer at rest.
  17. sophiecentaur

    sophiecentaur 14,717
    Science Advisor
    Gold Member

    I think that you can get over this quandry if you just discuss the momentum given to the ions. That's what would be conserved and provide the added momentum of the ship.
  18. What about instead of looking at it in terms of distance we look at it in terms of time. To the Universe all points of space and time are the same. If we could make a further point in space closer to us in time we would not need to travel such long distances, which may not be possible at all.

    And although we cannot reach the speed of light we can keep getting closer, and eventually we'll reach speeds where we can reach mars in hours, yet we never come close to the speed of light.
  19. There is a 'Plan B': Come the day your descendant can upload him/her/itself into a 'computer', that can be sent off at modest sub-light speed, but with the system clock set to 'very slow' so 'apparent' time is tolerable. Yes, okay, that runs right into the Fermi paradox...
  20. Ryan_m_b

    Staff: Mentor

    Making a further point in space closer? This has no basis in any contemporary or speculative understanding. The only proposals for something similar are wormholes and warpdrives addressed at the start of this thread.

    This post is overly speculative. There have been discussions recently on mind uploading here, the issue is too filled in with self appointed experts who know nothing of the field (*cough Kurzweil *cough). It may be possible but it's crackpottery at the moment. If you wan't a specific discussion on this I would suggest you start another thread.
    Last edited: Jul 20, 2011
  21. There is some speculative understanding of this - although purely as a thought experiment. The basic premise involved somehow altering the curvature of space, to "squash" space in front and "expand" it in the back of a space ship. This allows for a stationary object to "move" through space by warping space/time, thereby C can be sidestepped by effectively using controlled expansion.

    This is called the Alcubbierre drive and relies on something called the Alcubbierre metric for spacetime modification.This is essentially a "warp drive" and is no way even a theory, it is just a thought expirement but holds for an interesting concept.

    Personally I do not think this has any bearing on the real physical world - and I do not think any level of technologies will allow a Star Trek type federation of humans. I just do not think we will EVER have interstellar travel capabilities at any point in our future, I also think it highly unlikely any species anywhere in the U can develop this level of physical control over our U. I do not refute alien lifeforms - I think it numerous in both simople and more advanced forms. However I believe the HUGE distances, IMMENSE energy, UNBELIEVABLE resources and technological deficiencies are all answers to Fermis great question.
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