If Traveling At Light Speed Towards a Planet...

[p1t1o]

13 hours ago, Green Baron said:

Well, the original question was "if we could travel at the speed of light".

I understand it like this: as the traveler approaches c space contracts ever more and time passes ever faster, relative to an outside observer. At c (or better at the speed limit, which is strongly assumed to be c but might be just a little bit above) space is infinitely contracted and time infinitely compressed. Imagine, no space, no entropy, no time.

Edit: "10 years into the journey" indeed does not make sense since the journey at the speed of light does not take time. On the other hand, for an outside observer, it takes infinite time.

This is for a fictitious traveler at exactly the speed limit and does not contradict the calculations for a journey with a speed just below c.

Hope that was not totally wrong ...

I thiiiink that at 1.0c, (if the universe didn't implode) the trip would appear to take exactly 40 years for an outside observer.

For the traveller, the time it takes is not instant for time still flows normally within the ship  from the PoV of the traveler, but the "time it takes" is meaningless because the traveler observes time to have stopped outside his ship.

Time within and without the ship is completely independent, I think.

**

Of course all of that is wrong because its impossible, we are literally talking about something outside the rules. 

It would be just as correct to say that everything turns into chocolate at 1.0c, the laws of physics like that idea about the same.

Edited February 24, 2017 by p1t1o

[Green Baron]

Well, it was a play of thoughts. Yes, it's a bit like asking "what does physics say if we ignore physics ?" :-)

[p1t1o]

19 minutes ago, Green Baron said:

Well, it was a play of thoughts. Yes, it's a bit like asking "what does physics say if we ignore physics ?" :-)

lol really I was just covering my back in case someone has a much better idea lolol

[bewing]

OTOH, it's not as simple as the physics people here imply, quite. Their relativity calculations are good. The whole dilemma about reaching exactly lightspeed seems accurate. The causality violation with an FTL transmitter is indeed a problem. (With the caveat that it's not mass that increases to infinity at lightspeed -- it's momentum!) It's also true that the Lorentz equations break down at FTL speeds. You end up taking a square root of a negative number (but that's mathematically/physically fixable).

 

However, scientists have also known for more than half a century that when an atom decays radioactively and releases and alpha-particle -- the alpha particle is ejected from the nucleus at FTL speeds. Additionally, if you shoot a maser beam through a block of copper, the photons in the maser beam travel FTL while they are in the copper. They have even sent a Bach sonata FTL through a block of copper. In fact, it seems that any quantum tunneling process happens FTL. And the early universe also expanded at an FTL rate. (Astrophysicists call it "inflation" to dodge the issue.) That early universe expansion was probably also due to quantum tunneling effects (too much mass/energy confined to too small an area tends to violate the Uncertainty Principle.)

So all this about "FTL is impossible, blah, blah, blah" stuff is a bit head-in-the-sandish.

 

[p1t1o]

4 hours ago, bewing said:

However, scientists have also known for more than half a century that when an atom decays radioactively and releases and alpha-particle -- the alpha particle is ejected from the nucleus at FTL speeds. Additionally, if you shoot a maser beam through a block of copper, the photons in the maser beam travel FTL while they are in the copper. They have even sent a Bach sonata FTL through a block of copper. In fact, it seems that any quantum tunneling process happens FTL. And the early universe also expanded at an FTL rate. (Astrophysicists call it "inflation" to dodge the issue.) That early universe expansion was probably also due to quantum tunneling effects (too much mass/energy confined to too small an area tends to violate the Uncertainty Principle.)

So all this about "FTL is impossible, blah, blah, blah" stuff is a bit head-in-the-sandish.

No malice, but I feel 100% confident in telling you that you may have interpreted something incorrectly. No-FTL is one of the hardest-standing laws in the physical world.

Note that it is possible for a wave to have a phase or group velocity above c, but there is nothing actually travelling above c. It is analogous to how a shadow could be made to move across a surface above c.

There are also caveats that can be made with the expansion of space itself, but again, there is nothing that is moving locally faster than c.

I've never heard of alpha decay violating FTL, in fact they are known for being particularly slow. I'd love to see a source for that. Ah no, wait, its probably related to quantum tunelling and how the particle escapes the nucleus, see below.

In the quantum physics world, things get weird ok. But even with "spooky action at a distance" there has yet to be any sign of even information (lat alone some matter) being transmitted FTL. Einstein might not have liked the idea, but that doesn't mean that special relativity goes out the window.

Special Relativity is one of the most sturdy, supported, observed theories in the scientific world. I cannot state that highly enough.

The Heisenberg uncertainty principle is another source of confusion for many - when you dont know exactly where a particle, and then you suddenly find it somewhere unexpected, it can appear to have moved fast, but again, there has yet to be any known mechanism for moving mass FTL.

As for quantum tunneling, there have been some weird results, but whether or not something was actually travelling FTL is still highly spurious at this time. It has definitely been found, for example, that there is no causality violation, and another team found no violation of special relativity at all (something to do with very complicated particle physics that goes over my head).

Clearly what exactly is happening during quantum tunneling processes is not yet 100% understood, but that is a far far cray from "a bit head-in-the-sandish".

1 intriguing journal paper does not an overturning of special relativity make, same goes for any other physical concept. If anything, treating single results with such importance is putting your head in the sand. 

Im open to the idea of the FTL barrier being broken in a significant way, if that is the way it turns out, but we are far from that point. Not everything is possible, after all.

At this point, "No-FTL is one of the hardest-standing laws in the physical world." is one of the safest statements that you can make.

There is definitely a lot of interesting and weird stuff going on in the quantum world these days, but we are not at FTL yet

***

4 hours ago, bewing said:

(With the caveat that it's not mass that increases to infinity at lightspeed -- it's momentum!)

It is neither mass nor momentum. Both of those are classical concepts.

Relativistic-mass has been stated to be the increasing property, though this term has its problems.

It is probably safest, and most correct, to say that "Energy increases without bound as v->c".

***

Edited that last part a few times, think Im pretty happy with it now.

Edited February 24, 2017 by p1t1o
increased reasonableness and robustness

[Green Baron]

Yes, something must have been misinterpreted with the faster than light thing.

And it is actually the mass that increases with speed. The mass is as relative as time and distance with m(v) = m0 / sqrt( 1 - v²/c² ) or m0 times Lorentz-factor if you like, where m0 is rest mass and v is the speed of the reference system. Maybe it is easier to accept if we say that the rest mass (f.e. of a particle) is fixed in every reference system, but the v-dependent mass changes.

 

I could not find an explanation about relativity that states anything about what happens at the speed of light. The formulas only serve until very short before. It is nice to play with "everywhere at no time" at the speed of light, but right now i doubt it's still physics ...

I wish a physicist would show up :-)

 

p.s.: Bach, really ? I would have taken Beethoven.

 

Edit: as to the inflationary expansion: nothing moved in a relative sense during that phase, as the galaxies outside of our hubble sphere are not actually moving ftl. It is the space itself that expands, taking everything with it. So, if you accelerate in any direction, you will still take your personal "hubble sphere" with you, but it is at any speed impossible to catch up with this expansion. The last thing i read from cosmologists is that it might well be possible that there is no limit to the expansion of space. I know, it is against intuition, but nevertheless it is :-) Relativity is not harmed by the expansion, since any acceleration you give to an object ends short before c.

 

Edited February 24, 2017 by Green Baron

[p1t1o]

1 hour ago, Green Baron said:

I could not find an explanation about relativity that states anything about what happens at the speed of light. The formulas only serve until very short before. It is nice to play with "everywhere at no time" at the speed of light, but right now i doubt it's still physics ...

A good mathematical model will spit out garbage if you enter impossible conditions, I doubt there is an explanation anywhere!

Even the folks in the papers that describe what bewing was talking about (FTL in quantum tunelling) noted that a zero-time event "has no physical reality", because zero-time implies infinite enery (and probably lots more complex science and maths to that effect.) Hence their paper whilst interesting and apparently high-quality, does not disprove Special Relativity in one fell swoop.

Edited February 24, 2017 by p1t1o

[Steel]

To add to all of the above, if any of the things that @bewing raised earlier actually violated relativity then there would have been a HUGE uproar in the scientific community. There are experiments that appear FTLish, but I don't think there is a single one where anyone has reason to believe that relativity has been violated.

[K^2]

On 2/24/2017 at 9:19 AM, Green Baron said:

I could not find an explanation about relativity that states anything about what happens at the speed of light.

What you should be searching for is Light-Front Coordinates. That is the mathematics for limit v→c. It's not going to be terribly helpful for this discussion, though. The only practical ways of traveling at light speed involve event horizons, warp bubbles, wormholes, or some other distortions of space-time preventing a hard singularity that would arise otherwise if you tried to drag anything with a mass shell at these speeds.

[DrowElfMorwen]

Sorry, this is the OP. I feel no one saw my second, follow up post clarifying a better scenerip to ask my quastions. So I'm still not quite sure what the answers are.

[K^2]

9 minutes ago, DrowElfMorwen said:

Sorry, this is the OP. I feel no one saw my second, follow up post clarifying a better scenerip to ask my quastions. So I'm still not quite sure what the answers are.

Scientist A will only experience a few years during his trip. (A little less than 2 years at 0.999c) During these years, he will see planet he's flying towards age 80 years. 40 to account for distance and 40 more for duration of the trip. And yes, it will take scientist B 80 years to see scientist A arrive at destination planet, making the two observations consistent.

See Wikipedia's article on Twin Paradox for some notes on how to think through such an experiment.

[DrowElfMorwen]

Thank you K^2, I don't know why I didn't think to look up the Twin Paradox.

Now imagine how cool it would be to record such an aging of a planet on a ship. Sure, we might not see much change except for clouds and an ocean, if its there, but it'd still be cool.