National Geographic: Fake News?

[Dan]

Today I read an article in National Geographic claiming that a quarter of the 4000 exoplanets discovered by the Kepler space telescope are Earth-sized planets situated in the habitable zone of their stars. Assuming that each of the 100 billion stars in the Milky Way galaxy has at least one planet, that gives at least 25 billion Earth-sized planets in the habitable zone in our galaxy!

However I then read an article in New Scientist saying that only 49 of the discovered exoplanets are in the habitable zone (where water can exist as a liquid) and of these only 8 are in the abiogenesis zone (where the amount of UV light is just right). Of these 8, 7 are believed to be gaseous (as their radii are greater than the 1.7 Earth radius limit), leaving only one planet out of 4000, Kepler 452B, as potentially harbouring life!

Also, over half of the exoplanets are candidates yet to be confirmed, including Kepler 452B. So we really know of only two Earth-sized planets in both the habitable and abiogenesis zones, Earth and Mars.

How can National Geographic print something so misleading?

[rprosperi]

(04-05-2019 06:54 AM)Dan Wrote:  How can National Geographic print something so misleading?

I don't follow this closely, just an armchair fan that reads Astronomy magazine, but I'm quite sure the New Scientist summary is much closer to the facts.

Perhaps a closer reading of the Nat Geo article will reveal some additional qualifiers, even if stated poorly, to make the "about half" number closer to the truth.

While it's true that various sources quote very different numbers and types of habitable exoplanets, all I've read imply the number is quite small when all factors are included.

[Eddie W. Shore]

I would love to get to the day we are traveling in space like Star Trek so we can find the actual number for ourselves. That's a long way away though.

[David Hayden]

(04-05-2019 12:41 PM)Eddie W. Shore Wrote:  I would love to get to the day we are traveling in space like Star Trek so we can find the actual number for ourselves. That's a long way away though.

I don't know if we'll ever travel through space like in Star Trek, but we might make phone calls that way. The theory of relativity says that you can't travel at the speed of light, but it doesn't say you can't travel faster. Quantum mechanics says that everything happens in quanta, including velocity.

So imagine if we could accelerate atomic particles to just below the speed of light, and then cause its velocity to make a leap to just above the speed of light? Such a thing could then be accelerated even faster and used as a communications carrier.

[Thomas Okken]

(04-07-2019 01:34 PM)David Hayden Wrote:  I don't know if we'll ever travel through space like in Star Trek, but we might make phone calls that way. The theory of relativity says that you can't travel at the speed of light, but it doesn't say you can't travel faster.

The time dilation formula suggests you can't...
\[Δt' = \frac{Δt}{\sqrt{1-\frac{v^2}{c^2}}}\]
When \(v=c\) you get a division by zero, so that's clearly no good, but when \(v>c\), the time dilation (and relativistic mass) become imaginary, so how is that supposed to correspond to any physical reality?

[Csaba Tizedes]

(04-07-2019 01:57 PM)Thomas Okken Wrote:  

(04-07-2019 01:34 PM)David Hayden Wrote:  The theory of relativity says that you can't travel at the speed of light...

The time dilation formula suggests you can't...
\[Δt' = \frac{Δt}{\sqrt{1-\frac{v^2}{c^2}}}\]
When \(v=c\) you get a division by zero...

Hmm..., because we can't to divide anything with zero we can't travel with the speed of light? Strange.
BTW we have some information about imaginary numbers, therefore we can travel above?!

[rprosperi]

(04-07-2019 01:57 PM)Thomas Okken Wrote:  When \(v=c\) you get a division by zero, so that's clearly no good, but when \(v>c\), the time dilation (and relativistic mass) become imaginary, so how is that supposed to correspond to any physical reality?

If one can devise a method to surpass the speed of light, you get a free pass on breaking other laws. Also I imagine traveling beyond the speed if light is cool.

[mfleming]

(04-07-2019 01:57 PM)Thomas Okken Wrote:  When \(v=c\) you get a division by zero, so that's clearly no good, but when \(v>c\), the time dilation (and relativistic mass) become imaginary, so how is that supposed to correspond to any physical reality?

Jump to Hyperspace! Then we can make the Kessel Run in less than twelve parsecs!

[Valentin Albillo]

(04-07-2019 02:10 PM)rprosperi Wrote:  

(04-07-2019 01:57 PM)Thomas Okken Wrote:  When \(v=c\) you get a division by zero, so that's clearly no good, but when \(v>c\), the time dilation (and relativistic mass) become imaginary, so how is that supposed to correspond to any physical reality?

If one can devise a method to surpass the speed of light, you get a free pass on breaking other laws. Also I imagine traveling beyond the speed if light is cool.

Indeed. Besides, travelling faster than the speed of light, while not forbidden by relativity, implies being able to time-travel to the past, which would then potentially generate all kind of causality paradoxes, which is deemed physical laws wouldn't allow as it would destroy consistency wholesale.

Some of the paradoxes are much worse from a logical point of view than simply killing your own grandfather, see:

Tachyonic antitelephone

Best regards and have a nice remaining weekend.

V.
.

[Thomas Okken]

(04-07-2019 10:08 PM)Valentin Albillo Wrote:  travelling faster than the speed of light, while not forbidden by relativity, implies being able to time-travel to the past

How so? It's a popular sci-fi trope, sure, but the way I see it, traveling to the past would require negative time dilation. Imaginary time dilation would do what, exactly? Going sideways in time? Hmm, that sounds like the title of a sci-fi story I read many years ago.

[toml_12953]

(04-07-2019 01:34 PM)David Hayden Wrote:  

(04-05-2019 12:41 PM)Eddie W. Shore Wrote:  I would love to get to the day we are traveling in space like Star Trek so we can find the actual number for ourselves. That's a long way away though.

I don't know if we'll ever travel through space like in Star Trek, but we might make phone calls that way. The theory of relativity says that you can't travel at the speed of light, but it doesn't say you can't travel faster. Quantum mechanics says that everything happens in quanta, including velocity.

So imagine if we could accelerate atomic particles to just below the speed of light, and then cause its velocity to make a leap to just above the speed of light? Such a thing could then be accelerated even faster and used as a communications carrier.

You don't have to travel faster than the speed of light to get from one point to another faster than light would. If you could compress or fold space in front of you, it would seem like you were traveling faster than light (it would take less than a year to travel one light-year) but Einstein's calculations would be intact. Here's one report: https://www.space.com/2129-research-warp...drive.html I don't think I'll live to see it but maybe the near ancestors of a Kirk, Picard or Janeway are alive today.

[Valentin Albillo]

(04-07-2019 11:01 PM)Thomas Okken Wrote:  

(04-07-2019 10:08 PM)Valentin Albillo Wrote:  travelling faster than the speed of light, while not forbidden by relativity, implies being able to time-travel to the past

How so?

The link I posted explains it in great detail and includes several extensively detailed examples, even all the way to numeric results. I suggest you have a look at it. Rudy Rucker also explains this in very understandable terms in several of his books.

The conclusion is clear: at FTL speeds effects can precede causes, which is likely to result in paradoxes. By way of contradiction, if paradoxes can't actually occur in the physical Universe, then information can't travel at FTL speeds and both matter/energy and messages are but information.

Speaking of sci-fi novels I've been pretty fond all my life of Asimov's and he usually had its starships going from one point in the galaxy to another by means of instantaneous hyperspace jumps, a la Battlestar Galactica, explicitly pointing that FTL speeds in normal space were impossible in his fiction universe.

V.
.