8 ms·

It's never wrong to confirm by experiment, but there was never really any doubt among professional physicists that antimatter falls down. Similar doubts are exp

It's never wrong to confirm by experiment, but there was never really any doubt among professional physicists that antimatter falls down. Similar doubts are expressed about the feasibility of the warp drive by Alcubierre himself: https://twitter.com/malcubierre/status/362011821277839360 https://twitter.com/malcubierre/status/362011821277839360

marcosdumay 3y ago
I don't think anybody expects a wrap driver to be possible. It's just one of those odd things where the math says something, and it's well work looking at just in case. (Just like negative mass matter is something that nobody expects to exist, but likes to appear on equations here and there.) That said, I don't follow it closely, but didn't somebody recently worked out one that works without negative mass matter?
- distract8901 3y ago
  >That said, I don't follow it closely, but didn't somebody recently worked out one that works without negative mass matter? Yes. There was recently a few papers published showing that a static warp field is mathematically possible without negative energy. However, the field doesn't move or impart acceleration on its own. The best you can do is drag the warp field behind your ship with normal thrusters. Such a field seems to be pretty useless right now, but maybe that research will lead to something else in a few years
  - lawlessone 3y ago
    >The best you can do is drag the warp field behind your ship with normal thrusters. Ok we can build a warp trebuchet.
    - distract8901 3y ago
      The static warp field doesn't allow you to go faster than light because it doesn't move relative to the generator. You can drag the field around at sublight speeds but that's about it. Though IIRC they played around with some different geometries that did move, but the energy required was many times more than the entire universe contains.
      - renewiltord 3y ago
        Without reading any of the mathematics, I propose the warplev equivalent of maglev trains. We build a long train of these devices that we then turn on and off at the right times in order to propel something. It's genius and I will be making a wikipedia page, .io domain, and putting up an Angelist RUV.
  - I_Am_Nous 3y ago
    Perhaps not useless, but definitely not as convenient as we hope warp technology will be someday. Could such a device be used as a way to improve thruster efficiency? If you can drag a large enough warp bubble with conventional thrusters, and it "slopes" space in front of you, could it make moving in the direction of the slope easier so you use less fuel?
    - distract8901 3y ago
      I don't remember the details, but they explored some different field geometries which were more useful, but required an impossible amount of energy. Like, more energy than the entire universe.
  - stouset 3y ago
    What exactly is this “warp field”, then?
    - nathan_compton 3y ago
      spacetime.
    - distract8901 3y ago
      It's pretty much what it says on the tin. A field which warps nearby space into a different shape. What that means is complicated to explain, but the gist of a warp drive is that you expand space behind you and compress space in front of you. The normal space in between gets pushed forward, ideally at speeds faster than light. There's lots of good explainers on YouTube if you want to learn more.
    - Prickle 3y ago
      There are generally speaking, two interpretations in scifi. I don't really understand the physics, so apologies if I get it wrong. 1. Better known as the "Alcubierre Drive", Compress space infront of you and expand the space behind. Essentially inching forward like the inch worm. (If we presume that visually, the inch worm stays in the hunched position and slides forward because our eyes cannot see it's movement) Doing this smoothly in theory lets you accelerate and decelerate infinitely. https://en.m.wikipedia.org/wiki/Alcubierre_drive https://en.m.wikipedia.org/wiki/Alcubierre_drive 2. Warp space infront of you to create gravity, and pull you forward. Essentially, you make a pot hole in space time, and "fall" into it. This is basically the same Alcubierre Drive, but without the expansion at the rear. 2.1: One version holds that pothole at a specified distance infront of the ship. 2.2: The other version creates the pothole, then removes it before you reach it.
      - geoffmunn 3y ago
        I've often wondered about option 2, but wouldn't that be very risky if you were near something/someone and you created a large gravitational field? Also, if this was common and you had lots of ships warping the gravity field then would that not be some kind of space pollution? I know space is big and all that, but this seems like an irresponsible option.
- jaybrendansmith 3y ago
  I always liked the neat dodge of hyperspace proposed by Larry Niven. Idea was that humans never noticed it in their experiments, because they always ran their tests on Earth, too close to a gravity well, where it resolved to a singularity. At this point I believe the hands on the other foot. It's not the speed of light - but causality itself - that's not allowed to be broken by the universe.
NoGravitas 3y ago
Even among people who hold out hope that a warp drive is physically possible (as opposed to merely mathematically possible), I don't think anyone ever suggested that antimatter was a candidate for the negative mass required by the equations. It's always been some kind of unobtainium.
- _3u10 3y ago
  Yeah in Star Trek lore isn’t matter antimatter reactions how they get the power for it and then “dilithium” crystals are what makes the field?
  - krapp 3y ago
    As I understand it, dilithium crystals control the matter/antimatter reaction somehow. Zephram Cochrane's first flight used a ship powered by a nuclear reactor, I think. The warp field is made with an array of "warp coils" which apparently require the large amount of energy from the matter/antimatter reaction to create a subspace distortion field that allows warp travel. What is subspace? It's never adequately explained, but sometimes monsters come out of it and kidnap you to a pocket dimension where they rearrange your organs.
    - matthewdgreen 3y ago
      At sufficient speeds it can also cause you to become a giant slug and have slug babies with your ship's captain, which nobody will ever mention again. https://en.wikipedia.org/wiki/Threshold_(Star_Trek:_Voyager) https://en.wikipedia.org/wiki/Threshold_(Star_Trek:_Voyager)
  - redwall_hp 3y ago
    Dilithium is a mediator for a deuterium/antimatter reaction that generates the fantastic amounts of power required. The warp field is generated by some sort of coils in the nacelles.
  - shiroiuma 3y ago
    Antimatter is only used because, when combined with matter, it has a higher energy density than anything else known, including fusion. That part is completely within known physics. The "dilithium" is used somehow to control the matter-antimatter reaction; they have nothing to do with the warp field. Why the writers came up with this I don't know, but it does make for a convenient plot device sometimes when they have some problem with dilithium mines on some distant planet. Like various hard-to-acquire materials today, there are political problems caused by the scarcity of dilithium, and this comes up in many episodes. And, conveniently, dilithium somehow can't be replicated by the regular matter replicators. The warp field is created by the warp nacelles. How? Who knows.
mst 3y ago
Agreed, though also I really appreciate this sort of "obvious" experiment, because the incentives really aren't set up to encourage it and we've been surprised often enough over the centuries that Actually Double Checking is probably something we should do more of. (there's a parallel here to 'more negative results' and 'more replications')
- mr_mitm 3y ago
  Yes, nobody expected to find a positive cosmological constant either. Well except Steven Weinberg kinda.
delecti 3y ago
It always seemed like a reasonable, but still big, assumption that antimatter behaved the same way under gravity. Anti-particles have opposite charge, so maybe it could have made sense that they have opposite "gravitational charge"? But also gravity doesn't have "charge". So yeah, agreed. A good thing to confirm, even if (especially if) they expected the result to be unexciting.
- PaulHoule 3y ago
  Not a big assumption at all. Gravity is believed to be a property of space as opposed to a property of matter. That is, a satellite orbiting around the Earth is really going in a straight line but space is curved. Seen that way it’s just insane that any kind of matter could fall up. See https://en.wikipedia.org/wiki/Equivalence_principle https://en.wikipedia.org/wiki/Equivalence_principle anti-matter falling up would be as crazy as superluminal neutrinos (which I have to admit I almost want to believe)
  - lIl-IIIl 3y ago
    Bu isn't it s property of matter (mass) that curves space?
    - blueprint 3y ago
      no, it is actually a property of the flux of energy density, which occurs across space and time, whatever those are.
      - PaulHoule 3y ago
        Antimatter is not to be confused with the hypothetical negative mass: https://en.wikipedia.org/wiki/Negative_mass https://en.wikipedia.org/wiki/Negative_mass A negative mass particle would repel a positive mass particle but be attracted by a positive mass particle so the two would accelerate to ever increasing speeds but the positive and negative kinetic energy would cancel out so energy would still be conserved.
    - 3y ago
OhNoNotAgain_99 3y ago
[dead]
blackkettle 3y ago
The author directly addresses this sentiment in the concluding paragraph: > Although there are physicists who wonder “Why did we even need to do this experiment; we all knew that antimatter has positive mass,” that sentiment is absolutely foolish. We must remember — and I say this as a theoretical physicist myself — that physics is 100% an experimental science. We can be confident in our theory’s predictions only insofar as we can test and measure what it predicts; as soon as we step outside of the realm of what’s been validated by experiment, we run the risk of stepping outside the realm of where our theory is valid. We just learned that Einstein’s general relativity passed another test, the antimatter test, and with it, our greatest science-fiction hope for achieving warp drive has completely evaporated.
- otikik 3y ago
  Indeed. "Why do we need to measure the speed of light coming from a moving source. We all know that the velocity of all objects compounds with the velocity of their emitter"

marcosdumay 3y ago

I don't think anybody expects a wrap driver to be possible. It's just one of those odd things where the math says something, and it's well work looking at just in case. (Just like negative mass matter is something that nobody expects to exist, but likes to appear on equations here and there.) That said, I don't follow it closely, but didn't somebody recently worked out one that works without negative mass matter?

distract8901 3y ago
>That said, I don't follow it closely, but didn't somebody recently worked out one that works without negative mass matter? Yes. There was recently a few papers published showing that a static warp field is mathematically possible without negative energy. However, the field doesn't move or impart acceleration on its own. The best you can do is drag the warp field behind your ship with normal thrusters. Such a field seems to be pretty useless right now, but maybe that research will lead to something else in a few years
- lawlessone 3y ago
  >The best you can do is drag the warp field behind your ship with normal thrusters. Ok we can build a warp trebuchet.
  - distract8901 3y ago
    The static warp field doesn't allow you to go faster than light because it doesn't move relative to the generator. You can drag the field around at sublight speeds but that's about it. Though IIRC they played around with some different geometries that did move, but the energy required was many times more than the entire universe contains.
    - renewiltord 3y ago
      Without reading any of the mathematics, I propose the warplev equivalent of maglev trains. We build a long train of these devices that we then turn on and off at the right times in order to propel something. It's genius and I will be making a wikipedia page, .io domain, and putting up an Angelist RUV.
- I_Am_Nous 3y ago
  Perhaps not useless, but definitely not as convenient as we hope warp technology will be someday. Could such a device be used as a way to improve thruster efficiency? If you can drag a large enough warp bubble with conventional thrusters, and it "slopes" space in front of you, could it make moving in the direction of the slope easier so you use less fuel?
  - distract8901 3y ago
    I don't remember the details, but they explored some different field geometries which were more useful, but required an impossible amount of energy. Like, more energy than the entire universe.
- stouset 3y ago
  What exactly is this “warp field”, then?
  - nathan_compton 3y ago
    spacetime.
  - distract8901 3y ago
    It's pretty much what it says on the tin. A field which warps nearby space into a different shape. What that means is complicated to explain, but the gist of a warp drive is that you expand space behind you and compress space in front of you. The normal space in between gets pushed forward, ideally at speeds faster than light. There's lots of good explainers on YouTube if you want to learn more.
  - Prickle 3y ago
    There are generally speaking, two interpretations in scifi. I don't really understand the physics, so apologies if I get it wrong. 1. Better known as the "Alcubierre Drive", Compress space infront of you and expand the space behind. Essentially inching forward like the inch worm. (If we presume that visually, the inch worm stays in the hunched position and slides forward because our eyes cannot see it's movement) Doing this smoothly in theory lets you accelerate and decelerate infinitely. https://en.m.wikipedia.org/wiki/Alcubierre_drive https://en.m.wikipedia.org/wiki/Alcubierre_drive 2. Warp space infront of you to create gravity, and pull you forward. Essentially, you make a pot hole in space time, and "fall" into it. This is basically the same Alcubierre Drive, but without the expansion at the rear. 2.1: One version holds that pothole at a specified distance infront of the ship. 2.2: The other version creates the pothole, then removes it before you reach it.
    - geoffmunn 3y ago
      I've often wondered about option 2, but wouldn't that be very risky if you were near something/someone and you created a large gravitational field? Also, if this was common and you had lots of ships warping the gravity field then would that not be some kind of space pollution? I know space is big and all that, but this seems like an irresponsible option.
jaybrendansmith 3y ago
I always liked the neat dodge of hyperspace proposed by Larry Niven. Idea was that humans never noticed it in their experiments, because they always ran their tests on Earth, too close to a gravity well, where it resolved to a singularity. At this point I believe the hands on the other foot. It's not the speed of light - but causality itself - that's not allowed to be broken by the universe.

NoGravitas 3y ago

Even among people who hold out hope that a warp drive is physically possible (as opposed to merely mathematically possible), I don't think anyone ever suggested that antimatter was a candidate for the negative mass required by the equations. It's always been some kind of unobtainium.

_3u10 3y ago
Yeah in Star Trek lore isn’t matter antimatter reactions how they get the power for it and then “dilithium” crystals are what makes the field?
- krapp 3y ago
  As I understand it, dilithium crystals control the matter/antimatter reaction somehow. Zephram Cochrane's first flight used a ship powered by a nuclear reactor, I think. The warp field is made with an array of "warp coils" which apparently require the large amount of energy from the matter/antimatter reaction to create a subspace distortion field that allows warp travel. What is subspace? It's never adequately explained, but sometimes monsters come out of it and kidnap you to a pocket dimension where they rearrange your organs.
  - matthewdgreen 3y ago
    At sufficient speeds it can also cause you to become a giant slug and have slug babies with your ship's captain, which nobody will ever mention again. https://en.wikipedia.org/wiki/Threshold_(Star_Trek:_Voyager) https://en.wikipedia.org/wiki/Threshold_(Star_Trek:_Voyager)
- redwall_hp 3y ago
  Dilithium is a mediator for a deuterium/antimatter reaction that generates the fantastic amounts of power required. The warp field is generated by some sort of coils in the nacelles.
- shiroiuma 3y ago
  Antimatter is only used because, when combined with matter, it has a higher energy density than anything else known, including fusion. That part is completely within known physics. The "dilithium" is used somehow to control the matter-antimatter reaction; they have nothing to do with the warp field. Why the writers came up with this I don't know, but it does make for a convenient plot device sometimes when they have some problem with dilithium mines on some distant planet. Like various hard-to-acquire materials today, there are political problems caused by the scarcity of dilithium, and this comes up in many episodes. And, conveniently, dilithium somehow can't be replicated by the regular matter replicators. The warp field is created by the warp nacelles. How? Who knows.

mst 3y ago

Agreed, though also I really appreciate this sort of "obvious" experiment, because the incentives really aren't set up to encourage it and we've been surprised often enough over the centuries that Actually Double Checking is probably something we should do more of. (there's a parallel here to 'more negative results' and 'more replications')

mr_mitm 3y ago
Yes, nobody expected to find a positive cosmological constant either. Well except Steven Weinberg kinda.

delecti 3y ago

It always seemed like a reasonable, but still big, assumption that antimatter behaved the same way under gravity. Anti-particles have opposite charge, so maybe it could have made sense that they have opposite "gravitational charge"? But also gravity doesn't have "charge". So yeah, agreed. A good thing to confirm, even if (especially if) they expected the result to be unexciting.

PaulHoule 3y ago
Not a big assumption at all. Gravity is believed to be a property of space as opposed to a property of matter. That is, a satellite orbiting around the Earth is really going in a straight line but space is curved. Seen that way it’s just insane that any kind of matter could fall up. See https://en.wikipedia.org/wiki/Equivalence_principle https://en.wikipedia.org/wiki/Equivalence_principle anti-matter falling up would be as crazy as superluminal neutrinos (which I have to admit I almost want to believe)
- lIl-IIIl 3y ago
  Bu isn't it s property of matter (mass) that curves space?
  - blueprint 3y ago
    no, it is actually a property of the flux of energy density, which occurs across space and time, whatever those are.
    - PaulHoule 3y ago
      Antimatter is not to be confused with the hypothetical negative mass: https://en.wikipedia.org/wiki/Negative_mass https://en.wikipedia.org/wiki/Negative_mass A negative mass particle would repel a positive mass particle but be attracted by a positive mass particle so the two would accelerate to ever increasing speeds but the positive and negative kinetic energy would cancel out so energy would still be conserved.
  - 3y ago

OhNoNotAgain_99 3y ago

[dead]

blackkettle 3y ago

The author directly addresses this sentiment in the concluding paragraph: > Although there are physicists who wonder “Why did we even need to do this experiment; we all knew that antimatter has positive mass,” that sentiment is absolutely foolish. We must remember — and I say this as a theoretical physicist myself — that physics is 100% an experimental science. We can be confident in our theory’s predictions only insofar as we can test and measure what it predicts; as soon as we step outside of the realm of what’s been validated by experiment, we run the risk of stepping outside the realm of where our theory is valid. We just learned that Einstein’s general relativity passed another test, the antimatter test, and with it, our greatest science-fiction hope for achieving warp drive has completely evaporated.

otikik 3y ago
Indeed. "Why do we need to measure the speed of light coming from a moving source. We all know that the velocity of all objects compounds with the velocity of their emitter"