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Space and Astronomy Thread
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njp
14-02-2016
Originally Posted by MinaH:
“So for interstellar travel - time dilation would be something relevant to take into account when estimating the ages of the spaceship occupants when arriving at various stellar systems having travelled close to the speed of light during the course of the trip.”

Except that the prospects of getting close enough to the speed of light for time dilation to matter are not good. The amount of energy required is the killer. And the engineering. That's a killer too.
FIN-MAN
14-02-2016
Originally Posted by WhatJoeThinks:
“Good call. I'm not a big fan of his documentaries but here, ad libbing, he was on great form. +1

I've been thinking a lot about gravitational waves and this video kind of confirmed it. LIGO was essentially a highly-advanced seismometer, but where all of the seismic data has to be removed so that we can concentrate on the 'background noise'. Considering the cacophony that their supercomputers are having to sift through it bodes very well for future space-based gravitational-wave observatories.

The Hubble Space Telescope was a huge improvement over ground-based observatories, even though the atmosphere represents a relatively low-noise medium that adaptive optics can do a great job of attenuating. Even the human eye does a good job of picking stars out of the night sky. Gravitational waves on the other hand seem to be almost lost among the sounds of the Earth. The benefits of sending a GWO into orbit will be enormous.”

That was just a snippet from an hour long talk. They covered several scientific topics. It's really fascinating and as you said NGT ad-libbing is much better than when he is trying to follow a script.
Full Interview: https://www.youtube.com/watch?v=8RkyZvrHgOw
FIN-MAN
14-02-2016
Originally Posted by WhatJoeThinks:
“If I may..

If you were in interstellar space, for example, more time would have passed compared to that measured on Earth. And if you had been travelling along with the wave at the speed of light then no time would have seemed to have passed at all.

Is that what you meant, MinaH?

[Edit] It's fairly meaningless to equate light-years of distance to years of light travel, in my opinion. It completely misses the point that spacetime only conforms to human norms on human scales of space and time. It adds nothing to say, for example, that this distant collision between two black holes happened at the same time that stromatolites were the dominant lifeform on Earth, and it simply isn't true. Simultaneity, especially at such enormous distances, is an illusion. It assumes a universal 'now' that doesn't exist.”

Originally Posted by MinaH:
“WhatJoeThinks: Yes I think so. There is something called time dilation which means the faster you go the slower are your clocks relative to the "slower" reference frames. So if you were surfing the gravity wave at the speed of light you wouldn't age 1.3 billion years, I don't think you would age at all. But I am not sure you could physically be accelerated up to the speed of light only towards and close to it - so there would be some aging.

So for example super-accurate timepieces have been shown to be behind in time (running slow) after having travelled on the space shuttle or after having taken a number of trips on aircraft.

So for interstellar travel - time dilation would be something relevant to take into account when estimating the ages of the spaceship occupants when arriving at various stellar systems having travelled close to the speed of light during the course of the trip.”

Thank you both.

[Edit] My educational background is business and finance so I find science very fascinating. But I have to admit after listening to some of these scientists it gets to a point that it starts to sound like I'm listening to my stoner friend ponder about the meaning of things and I stop and say "what the hell did you just say"?
WhatJoeThinks
14-02-2016
Originally Posted by njp:
“Well, light years of distance are years of light travel, by definition...

I understand your point about simultaneity being illusory - different celestial observers will disagree about the ordering of these events - but I don't see why this should stop us talking about what was happening on Earth (one specific location) when the gravitational waves from these two distant black holes coalescing embarked on its journey.”

Because there is no 'when'! *Keanu Reeves' voice implied*

From the point of view of somebody living in the vicinity of the black hole merger, pointing their telescopes towards the Earth, the event would seem to have occurred during the neoarchean era (2.6 Gya), not the mesoproterozoic era (1.3 Gya). In reality, events are local phenomena by definition. The merger was one event, the LIGO detection was another, and the spacetime distance between them was a number of lightyears.
WhatJoeThinks
14-02-2016
Originally Posted by FIN-MAN:
“That was just a snippet from an hour long talk. They covered several scientific topics. It's really fascinating and as you said NGT ad-libbing is much better than when he is trying to follow a script.
Full Interview: https://www.youtube.com/watch?v=8RkyZvrHgOw”

Thanks for the link.
WhatJoeThinks
14-02-2016
Originally Posted by njp:
“Except that the prospects of getting close enough to the speed of light for time dilation to matter are not good. The amount of energy required is the killer. And the engineering. That's a killer too.”

Durrr... You forgot about warp drive!
Gordie1
14-02-2016
Originally Posted by MinaH:
“I think that 1.3 billion years is according to measurements in our reference frame (the earth). If you were surfing that gravitational ripple at the speed of light then it would be much much less than 1.3 billion years.”

Brian may wrote as song about that on Queens A night at the opera album.

https://www.youtube.com/watch?v=kE8kGMfXaFU
njp
14-02-2016
Originally Posted by WhatJoeThinks:
“From the point of view of somebody living in the vicinity of the black hole merger, pointing their telescopes towards the Earth, the event would seem to have occurred during the neoarchean era (2.6 Gya), not the mesoproterozoic era (1.3 Gya). In reality, events are local phenomena by definition.”

Your reasoning eludes me. Where did the 2.6 Gya figure come from?
MinaH
14-02-2016
Originally Posted by njp:
“Your reasoning eludes me. Where did the 2.6 Gya figure come from?”

I think what joe thinks meant is that from Earth the event happened 1.3 billion years ago. Now 1.3 billion years ago at the actual event, light from Earth falling in the vicinity of the actual event would have taken 1.3 billion years (assuming no universal expansion?) - so that is where the doubling occurs. I think that is what Joe meant but am not 100% certain.

Originally Posted by Gordie1:
“Brian may wrote as song about that on Queens A night at the opera album.

https://www.youtube.com/watch?v=kE8kGMfXaFU”

Thank you for posting this.
TelevisionUser
14-02-2016
Plan(et) Nine from Outer Space - on TV and online:

In California, Chris Lintott meets the astronomers whose study of the distant Kuiper Belt led them to predict the existence of the planet. And while some scientists are still sceptical, Maggie Aderin-Pocock discovers how our models of the formation of the solar system and the discovery of similar exoplanets around other stars all support the existence of Planet 9.

Mike Brown and Konstantin Batygin fully expect a new and undemotable ninth planet will be found in the outer reaches of the solar system. The Caltech researchers talk about their findings and much more. Emily Lakdawalla has made a wealth of Chinese lunar lander images much more accessible.
WhatJoeThinks
14-02-2016
Originally Posted by njp:
“Your reasoning eludes me. Where did the 2.6 Gya figure come from?”

Like MinaH said, if the black hole merger occurred 1.3 billion years ago, 1.3 billion lightyears from Earth, then the Earth would have appeared (to those in the vicinity of the merger with powerful telescopes) as it was 2.6 Gya - long before any stromatolites appeared.
njp
14-02-2016
Originally Posted by WhatJoeThinks:
“Like MinaH said, if the black hole merger occurred 1.3 billion years ago, 1.3 billion lightyears from Earth, then the Earth would have appeared (to those in the vicinity of the merger with powerful telescopes) as it was 2.6 Gya - long before any stromatolites appeared.”

This makes no sense to me.
WhatJoeThinks
15-02-2016
Originally Posted by njp:
“This makes no sense to me.”

If you view the Earth from 1.3 billion lightyears away it will look how it was 1.3 Gya. People living near the (merged) black hole 'today' would see the Earth teeming with stromatolites, but their ancestors living 1.3 Gya (who were there when the black holes merged) would have seen the Earth as it was 2.6 Gya.
brangdon
15-02-2016
Originally Posted by Rich Tea.:
“I've heard a couple of people wondering aloud about why we have not already discovered for definite this new and huge Planet 9 if it exists when it is in our comic backyard compared to those galaxies we can spot that are over 10 billion light years distant. To be honest and as much as I take an interest and knowledge in the subject I really do not have a decent answer to that question.”

Because galaxies are bigger and brighter than planets?
atg
15-02-2016
Originally Posted by WhatJoeThinks:
“If you view the Earth from 1.3 billion lightyears away it will look how it was 1.3 Gya. People living near the (merged) black hole 'today' would see the Earth teeming with stromatolites, but their ancestors living 1.3 Gya (who were there when the black holes merged) would have seen the Earth as it was 2.6 Gya.”

What is "Gya"? Bya would be more understandable.
njp
15-02-2016
Originally Posted by WhatJoeThinks:
“If you view the Earth from 1.3 billion lightyears away it will look how it was 1.3 Gya. People living near the (merged) black hole 'today' would see the Earth teeming with stromatolites, but their ancestors living 1.3 Gya (who were there when the black holes merged) would have seen the Earth as it was 2.6 Gya.”

But that's just a rather extreme example of observers in different places disagreeing about the order of events - as I acknowledged earlier. An observer midway between Earth and the black holes would see stromatolites and black holes coalescing as simultaneous events. Anyone elsewhere will disagree (I am of course pretending that 'stromatolites' were a comparably brief chronological blip!).

What remains true is that the gravitational waves recently observed on Earth embarked on their voyage across the cosmos 1.3 billion years ago. So I still don't understand why you would object to that way of putting the timescales involved into an Earthly context.
WhatJoeThinks
15-02-2016
Originally Posted by atg:
“What is "Gya"? Bya would be more understandable.”

It means "gigayears ago". Both are equally understandable, but the use of giga avoids any confusion as to whether billion refers to 10^9 or 10^12.
WhatJoeThinks
15-02-2016
Originally Posted by njp:
“But that's just a rather extreme example of observers in different places disagreeing about the order of events - as I acknowledged earlier. An observer midway between Earth and the black holes would see stromatolites and black holes coalescing as simultaneous events. Anyone elsewhere will disagree (I am of course pretending that 'stromatolites' were a comparably brief chronological blip!).

What remains true is that the gravitational waves recently observed on Earth embarked on their voyage across the cosmos 1.3 billion years ago. So I still don't understand why you would object to that way of putting the timescales involved into an Earthly context.”

Because it adds nothing to our understanding of spacetime to claim that a particular cosmic event happened "when Jesus was alive" or "when dinosaurs roamed the Earth" or whatever. What we know is that these gravitational waves have travelled 1.3 billion lightyears to get here. How long that journey took isn't necessarily a simple, euclidean corollary of that. The light from the 'edge' of the visible Universe some 46 billion lightyears away only took about 13.8 billion years to get here, for example, due to universal expansion.

The tabloid press like to convert things to earthly scales for their readers, presumably to make things simpler to understand, but what they really do is propagate the lack of comprehension of the journalist. Relativity isn't that difficult to understand really, it's just that nobody tries to educate children about it other than to instil the notion that such things are barely comprehensible and you'll have to be some kind of super brain if you ever expect to understand it. Which is a load of b*llocks, of course.
atg
15-02-2016
Originally Posted by WhatJoeThinks:
“It means "gigayears ago". Both are equally understandable, but the use of giga avoids any confusion as to whether billion refers to 10^9 or 10^12.”

There's no confusion over usage of the word "billion", except for people who are being deliberately obtuse. And I don't ever remember hearing the word "gigayear" either.

In fact you yourself used the phrase "billion lightyears away" in the same post as "Gya", so how confusing is that?
WhatJoeThinks
15-02-2016
Originally Posted by atg:
“There's no confusion over usage of the word "billion", except for people who are being deliberately obtuse. And I don't ever remember hearing the word "gigayear" either.

In fact you yourself used the phrase "billion lightyears away" in the same post as "Gya", so how confusing is that?”

To be clear, I don't find either confusing in the slightest. I was using what I understand to be standard terminology. When you asked why I used "Gya" instead of "Bya", which you said was "more understandable", I gave you the standard reasoning. I didn't invent that reasoning though.

I suppose I could have used "Gly" (gigalightyears) too, but it isn't a common abbreviation as far as I know, whereas "Gya" is. That isn't at all confusing unless, as you say, you are being deliberately obtuse.
swingaleg
16-02-2016
I still haven't got it clear in my mind why these gravitational waves travel at the speed of light

Are they thought to be some kind of electro-magnetic wave ?

I don't think that's the case as I understood the science has been trying for a century to find a relationship between gravity and electromagnetism and the other forces

I suspect that these waves not actually composed of waves of gravity but ripples in the fabric of the universe.........in the same way that 'gravity' doesn't really exist but is merely a handy description of the distortions in spacetime caused by mass

Does this sound as though I'm on the right track ?
atg
16-02-2016
Originally Posted by swingaleg:
“I still haven't got it clear in my mind why these gravitational waves travel at the speed of light

Are they thought to be some kind of electro-magnetic wave ?

I don't think that's the case as I understood the science has been trying for a century to find a relationship between gravity and electromagnetism and the other forces

I suspect that these waves not actually composed of waves of gravity but ripples in the fabric of the universe.........in the same way that 'gravity' doesn't really exist but is merely a handy description of the distortions in spacetime caused by mass

Does this sound as though I'm on the right track ?”

Definitely, yes.

Generally I think anything will travel at the speed of light unless there is a reason for it not to, such as having mass.

Since forces are associated with transmission particles, such as the photon for the electromagnetic force, there is a theoretical particle called a graviton which would transmit gravity. Since gravity waves travel at the speed of light this must presumably also be massless, like the photon.
MinaH
16-02-2016
Hi whatjoethinks , if you are happy with your previous comment, sometimes there is no need to keep explaining, as sometimes that takes one in circles.

For what it is worth I attach the following for atg, which provides adequate description of the various terminologies associated with prefixes used with the SI system of metrics:
https://en.wikipedia.org/wiki/Metric_prefix
MinaH
16-02-2016
Originally Posted by swingaleg:
“I still haven't got it clear in my mind why these gravitational waves travel at the speed of light

...

I suspect that these waves not actually composed of waves of gravity but ripples in the fabric of the universe.........in the same way that 'gravity' doesn't really exist but is merely a handy description of the distortions in spacetime caused by mass

Does this sound as though I'm on the right track ?”

Sounds reasonable. Although "gravity" not really existing is probably a play on words and the meaning ascribed to words ...
RobinOfLoxley
16-02-2016
46 billion! That's a lot of Nelson's Columns.
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