Speed of light and shiny planets

[Miranda]

Please bear with me... I am a complete (yet fascinated) noob to all things starry and sciency, so you will have to excuse the random and bizarre nature of this question..

When I look at stars I'm see light that is from light years away, its really really old as it's travelled so far away to get to us.

So, if I look at a planet, the light is travelling from the sun to say Jupiter, and then that reflects light and we see it in our sky.

So how 'old' is that light that we actually see?

I'm just really curious and I know someone here will be clever enough to know the answer

[jimmyjamjoejoe]

Well, sun to earth is about 8 minutes. Jupiter to earth is about 30minutes...

edit - so i guess when looking at Jupiter the light could be anything from 38 minutes, to 68 minutes old (assuming perfectly round orbits etc, which they probably aren't, but you get the idea...).

second edit - Those photons have also been bouncing around the core of the sun for millions if not billions of years after being ripped from atoms, slowly working their way to the surface before making the journey to our eye.

[Miranda]

Wow!!! Thanks Jimmyjamjoejoe..

Just thinking about those bouncing billion year old photons that went an extra 38-68 mins to get to my eye...

Woah, now that is making me speechless.

[Shibby]

Here's a headscratcher for you... Some objects are so distant that the universe hasn't been around long enough for the light from them to reach us! This is what defines the edge of the observable universe!

[redgiantjohn]

heres another thing that confuses me... if a planet is found by keplar orbiting a star millions of lightyears away and lets just say there are people on it and with a telescope they see our planet orbiting the sun but we see them as they were millions of years ago and they see us as we were millions of years ago so their 'now' is millions of years ago compared to our 'now' and vice versa so whos now is actually right? probably a stipid thing to say right? the concept of time confuses me i mean how long is 'now' a billionth of a second? i dont think now even exists as soon as its here its gone maybe the only way to describe time is through entropy or describe it as a location in the space-time 'loaf' as brian greene said. anyway im rambling utter nonsense so..... carry on as you were

[foundaplanet]

heres another thing that confuses me... if a planet is found by keplar orbiting a star millions of lightyears away and lets just say there are people on it and with a telescope they see our planet orbiting the sun but we see them as they were millions of years ago and they see us as we were millions of years ago so their 'now' is millions of years ago compared to our 'now' and vice versa so whos now is actually right? probably a stipid thing to say right? the concept of time confuses me i mean how long is 'now' a billionth of a second? i dont think now even exists as soon as its here its gone maybe the only way to describe time is through entropy or describe it as a location in the space-time 'loaf' as brian greene said. anyway im rambling utter nonsense so..... carry on as you were

I like it, thats really good...:D:D

[wired2moon]

heres another thing that confuses me... if a planet is found by keplar orbiting a star millions of lightyears away and lets just say there are people on it and with a telescope they see our planet orbiting the sun but we see them as they were millions of years ago and they see us as we were millions of years ago so their 'now' is millions of years ago compared to our 'now' and vice versa so whos now is actually right? probably a stipid thing to say right? the concept of time confuses me i mean how long is 'now' a billionth of a second? i dont think now even exists as soon as its here its gone maybe the only way to describe time is through entropy or describe it as a location in the space-time 'loaf' as brian greene said. anyway im rambling utter nonsense so..... carry on as you were

The concept of now is a purely relative thing, in your example their then is our now, their now is our yet to be, our then is their now, our now is their yet to be...

[Miranda]

I like it, thats really good...:D:D

agree! I really like redgiantjohn. I love stuff like this

Great thread

[jimmyjamjoejoe]

You'd love the book "Why does E=MC2 (and why should we care)"

The first 100 pages or so are pretty basic, but kind of gets your mind back into the swing of things as far as math and grasping theories goes. After the first 100 pages though, it gets pretty deep, and really opened my eyes as far as relativity is concerned. Quite a few things needed to be read 2-3 times, and some analogies are slightly hard to grasp, but once understood, you come to realize there is no easy way to explain such things.

Thankfully, you ~can~ skip over the maths for most of it, but there is a somewhat deeper understanding to be had if you take the time to run through it. The section on the "master equation" though... good god...

[Miranda]

Oh will get a kindle sample and see how I get on Thank you

[ollypenrice]

Just to add a thought; there are objects out there whose light will never reach us because the Hubble Flow (the expansion of the Universe) is carrying us away from the advancing beam at more than the speed of light. Such objects form part of the unobservable universe.

I don't think that the idea of a delay in the exchange of information is really all that radical, though, and can come up in everyday life. You can imagine a pregnant daughter writing to her mum saying, 'I'm due tomorrow!' and the letter arriving the day after the birth took place.

Or think of watching village cricket from the safety of the pub over the road. You see the batsman whack the ball and a moment later you hear the sound. Sound travels far slower than light but even light took a measurable time to reach you so the actual strike came before you saw it. All informtion needs time to travel, except...

Ah! Now it does get scary... There are experiments which suggest that thare can be an instantaneous exchange of information in the quantum world. Maybe the whole idea of past-present-future is fundamentlally incorrect or, at least, highly incomplete.

Olly

[redgiantjohn]

well said olly, i read something about probability wave and one electron somehow communicating with another across a distance instantly!! this kind of blew my mind!?!? faster than light transmission of information? there was talk of tachyons sending the information but think they are only theoretical. the quantum world does not make sense but at the same time its the most fascinating subject

[sowspace]

Then, if this is the case then if we travel 13.7 billion light years away then can we see the Big Bang ?

[themos]

whos now is actually right

There is no "right" now across the universe. That idea went down once Einstein was done with it. But there's a convenient reference frame for all inhabitants of the universe that places the Big Bang 13.7 billion years in the past. That is the so-called "comoving" frame. Somebody correct me if I'm wrong.

Then, if this is the case then if we travel 13.7 billion light years away then can we see the Big Bang ?

We cannot see the big bang. The universe was opaque for hundreds of thousands of years after it. What we can see is the moment when the universe became transparent, that receding wall of opaqueness is called the cosmic microwave background radiation.

I know that there is a huge emotional attraction to the idea that out retina see very old light when we look at a galaxy. However, we can never do this. Think about it: either your telescope or your eye lens had to curve light to make it focus. The way the bending is done is by some matter absorbing the photon (sorry, that long-lived photon is gone!), the energy going into an electron and then the electron radiating another photon. What you see are always photons emitted from inside your eye.

[jimmyjamjoejoe]

Ah! Now it does get scary... There are experiments which suggest that thare can be an instantaneous exchange of information in the quantum world. Maybe the whole idea of past-present-future is fundamentlally incorrect or, at least, highly incomplete.

Olly

Mmmmmm spooky action at a distance, that was a fun read

[symesie04]

Ah! Now it does get scary... There are experiments which suggest that thare can be an instantaneous exchange of information in the quantum world. Maybe the whole idea of past-present-future is fundamentlally incorrect or, at least, highly incomplete.

Olly

Its called Nonlocality. Which suggests that particles are able to transfer information instantly without any thus discovered form of interference. This is big news at the moment and large corporations and defence budgets are being spent on research as it is deemed this will lead to a unbreakable encryption code.

[Miranda]

I know that there is a huge emotional attraction to the idea that out retina see very old light when we look at a galaxy. However, we can never do this. Think about it: either your telescope or your eye lens had to curve light to make it focus. The way the bending is done is by some matter absorbing the photon (sorry, that long-lived photon is gone!), the energy going into an electron and then the electron radiating another photon. What you see are always photons emitted from inside your eye.

really?? Now that is another thing I didnt know - although not sure I wanted to know that! Kinda like the emotional/romantic option lol.

[themos]

Luckily, photons are indistinguishable from each other so it doesn't matter!

[Shibby]

Ah! Now it does get scary... There are experiments which suggest that thare can be an instantaneous exchange of information in the quantum world. Maybe the whole idea of past-present-future is fundamentlally incorrect or, at least, highly incomplete.

But not useful (classical) information, unfortunately! Very interesting potential application of quantum entanglement in encryption, but no instantaneous transmission of information is possible because you can't actually affect the state of the qubit. Bummer.

Edit: sorry - to clarify/correct that - by "affect" I mean "choose"

[Space Bat]

Interesting thought process Olly

Your views have changed over the time I have known -

Just need George and Thermos to hop over to the dark side now

[ollypenrice]

Then, if this is the case then if we travel 13.7 billion light years away then can we see the Big Bang ?

Remember that the universe is expanding so during the 13.7 billion years of light travel time the point from which the photon was sent and your eye have been moving apart at a rate of knots. The point of emission at the end of the 13.7 billion years is several times more than 13.7 billion LY. An object which sent a photon to you with a flight time of 13.7 billion years would be 13.7 billion light years away only if the both you and it were stationary with respect to each other and the universe were not expanding.

Olly

[Miranda]

Remind me to drink more tea before reading your posts Olly

And a translation guide for the physics challenged ones like myself.

[Space Bat]

Remember that the universe is expanding so during the 13.7 billion years of light travel time the point from which the photon was sent and your eye have been moving apart at a rate of knots. The point of emission at the end of the 13.7 billion years is several times more than 13.7 billion LY. An object which sent a photon to you with a flight time of 13.7 billion years would be 13.7 billion light years away only if the both you and it were stationary with respect to each other and the universe were not expanding.

Olly

That may be possible Olly - however who says Space and Time is uniform ?? Because if it isn't then that changes things somewhat

[ollypenrice]

That may be possible Olly - however who says Space and Time is uniform ?? Because if it isn't then that changes things somewhat

Ah yes. Its uniformity was just an assumption uncle Albert had to make in order to make a start. Perhaps this will be the next big revision? Do you think so?

Olly

[Space Bat]

After watching Steven Birkoff and infinity and beyond was quite a refreshing documentary - did you see it??? worth taking a look on iplayer...

For me I can't for the life of me think why the universe expanded both as space/spacetime and time in a uniform manner....