
Ways to travel at nearly the speed of light - dnetesn
https://phys.org/news/2019-05-ways.html
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cheerlessbog
Interestingly if we can find a way to accelerate at a gentle constant 1g it is
possible to take a round trip to the edge of the universe in the lifetime of
the traveler [1].

This neglects the expansion of the universe, the health and safety effects of
traveling near to the speed of light, and the fact that we do not know how to
do this (you would not be able to bring your own fuel). Nevertheless we do not
know why it should be physically impossible.

[1]
[https://en.m.wikipedia.org/wiki/Space_travel_using_constant_...](https://en.m.wikipedia.org/wiki/Space_travel_using_constant_acceleration?wprov=sfti1)

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jbotz
This a key fact that a lot of people seem to misunderstand, even a lot of
popular science journalists trying to explain relativity. But to me it really
illuminates the connection between space and time and the inviolability of c.
From your own perspective you can travel arbitrarily fast in terms of how much
you age inside your spaceship... but as you move faster in space, time in the
the Universe outside your ship appears to be moving faster as well such that
always more than a year will have passed outside for every lightyear you've
traveled, even if it was only days, hours, or minutes for you.

~~~
mirimir
Vernor Vinge does a great job with this in _A Fire Upon the Deep_ and _A
Deepness in the Sky_. I do wish that he had written more about Pham Numen and
the Qeng Ho, back in their Slow Zone heyday.

Alastair Reynolds also does a great job with this in his _Revelation Space_
trilogy, with his lighthuggers.

~~~
newsbinator
One of the most interesting parts to me of Pham Nuwen's character was his
relationship to his distant descendants.

Humans just aren't wired to consider family members beyond 3 or 4 generations
up and down.

Perhaps I'd feel the same general apathy as Pham Nuwen 20 generations down.
Then again, he had other familial issues that played a part.

~~~
mirimir
One started with him hiding in a nursing home, after faking his death. I don't
recall specifics, but I suppose that it's possible that _all_ of the other
characters are his descendants. And they had spent a _long_ time looking for
him.

In the other, he'd been resurrected by some godlike AI as a meatspace agent.
Millennia after the Qeng Ho era, I think.

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lucidguppy
What I always found interesting was you can go as fast as you want - to you,
going from here to alpha centauri could take just weeks for you if you had
enough energy - it's just that time would speed up around you so no matter
what everyone else would see you get there in 4.5 - 5 years.

And if I'm wrong, I apologize and would gladly hear the correct answer.

~~~
pixelHD
Isn’t it the opposite - time slows down for you when you move at relativistic
speeds, and hence you end up getting to alpha Centauri in 5years w.r.t clocks
at Centauri or earth?

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zamadatix
An object's relative speed to itself is always 0 (by definition) and so the
passage of time is always constant for every object. As you can guess by the
name of the theory there is also no "universal clock" or "0 speed" in the
universe to compare against, it's only possible to measure speed and the flow
of time relatively between objects.

For these reasons "time slows down for you when you move at relativistic
speeds" is really a bad way to think of it (and not how the math of the theory
actually works). It's much more proper to say things in the form "To <observer
a> it appeared as if the clock of <observer b> was <sped up|slowed down>".
E.g.:

To the traveler it appeared as if the clock of Alpha Centauri was sped up. To
Alpha Centauri it appeared as if the clock of the traveler was slowed down.

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saagarjha
> Yet all across space, from black holes to our near-Earth environment,
> particles are, in fact, being accelerated to incredible speeds, some even
> reaching 99.9% the speed of light.

Or that, but with a dozen more 9s in it: [https://en.wikipedia.org/wiki/Oh-My-
God_particle](https://en.wikipedia.org/wiki/Oh-My-God_particle)

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mLuby
Shielding at the speed of light is an interesting challenge.

The beginning of Alastair Reynolds's short story "Weather" (in "Galactic
North") addresses this.

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NotSammyHagar
The easy way to achieve this is get the other party to travel toward you at
.99c. Slightly more seriously, it's always interesting to think about how you
can have the universe expanding faster than c, and so you can't see it all.
You can also approach someone else at faster closing speed than c if both
parties are traveling where the sum of their velocities toward each other is
greater than c (like both are going at .6c).

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IIAOPSW
>You can also approach someone else at faster closing speed than c if both
parties are traveling where the sum of their velocities toward each other is
greater than c (like both are going at .6c).

In neither your reference frame or the other person's will it appear to be
true that your closing speed is faster than c.

However due to the speed of light delay you may perceive the other person as
going much faster than c, but this is strictly an illusion. For example, if I
were watching a near-light speed ship approaching earth in a telescope, I
might see it begin its journey and then see it arrive a few seconds later and
my monkey brain would conclude it made the whole trip in the time I was
watching it. In reality the light from when it started the trip is a few years
old.

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rightbyte
Would you expect a 0.99c spaceship to be "brighter" in the telescope than a
0.01c? I mean, the average power of the bouncing light on it should be higher,
right? Since it's gonna be years of light in a shorter time.

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jcims
There would be a doppler blueshift out of the visible spectrum i believe, but
quantity wouldn’t change much IIRC from this Myhrthbusters episode
[https://youtu.be/HtbJbi6Sswg](https://youtu.be/HtbJbi6Sswg)

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zamadatix
Note that Mythbusters video was revisited later in the series and the claims
reversed:
[https://mythresults.com/episode38](https://mythresults.com/episode38)

It's not an equivalent question either, the question is intensity not sum.

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jcims
Very cool, need to check that out.

However, isn't intensity equal to sum when it comes to light? At least in the
visible spectrum, more energy just shifts the wavelength...perceived intensity
comes from photon count.

~~~
zamadatix
Photons sent on a 5 year near c journey would arrive over e.g. 5 days instead
of 5 years, hence the intensity. I.e. it doesn't take 5 years for the light
you emitted 5 light days ago to arrive but the light you emitted 5 years ago
may only be 5 light day ahead.

