Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_imaging_challenge_banner_lunar_landings.thumb.jpg.b50378d0845690d8a03305a49923eb40.jpg

Patrick2568422

What happens if the universe expands faster than the speed of light?

Recommended Posts

Eventually, due to "dark energy", the universe will be expanding so quickly that it will break the speed of light. This, if I am not wrong, already happened at the beginning of the universe for 10 to the power of -43 seconds.  So, what will happen once the universe is expanding at that speed. Will the laws of objects moving faster than the speed of light apply (mass increasing, time slowing down ect.)?

I have to stress I am my no means an expert on the matter, if anyone could point out mistakes in this question please do. All answers would be much appreciated. 

Edited by Patrick2568422
  • Like 2

Share this post


Link to post
Share on other sites

No idea what the mass and time dilation issues would be but it would certainly limit the extent of the observable Universe.   :icon_biggrin:

  • Like 2

Share this post


Link to post
Share on other sites

I guess eventually we would be all alone in a freezing cold expanse !!

  • Like 1

Share this post


Link to post
Share on other sites

Presumably parts of it already are in relation to ourselves. Anything outside the Hubble Radius will be receeding from us at greater then C.

But get it understood that the objects are not themselves moving greater then C, but the gap between us and them is expanding at greater then C.

Look at it this way, place a box - nice stationary item - on one of the rubber walkway belts at Heathrow. How fast it is going?

It is stationary, the thing it is on is moving but it is not.

Spacetime is expanding and the distant galaxies are "on" that (as a stationary box is on the rubber belt), so they get carried away with it.

  • Like 2

Share this post


Link to post
Share on other sites

Not an expert, not by a long shot, but think of the universe like a glass of water, a big giant glass of nothing-water. In order for the universe to create mass and expand, it must occupy the nothing, similar to how a pebble enters water in a glass. It displaces the water, pushing its way through just as the universe displaces the "nothing" as it expands...so in theory...somewhere out there, there's a whole lot of nothing that's moving faster than the speed of light to make way for the universe as it expands.

 

Doesn't answer your question...but still interesting.  FYI this came from "how the universe works"....not my own brain lol 

  • Like 1

Share this post


Link to post
Share on other sites

exactly, nothing is actually moving through space faster than the speed of light. Those objects are near stationary in relation to space around them. There is no actual movement through space.
And this is happening right now. There are parts of the universe that are actually being "stretched out" away from us right now faster than the speed of light. And from their point of view, we-earthlings are also being stretched out away at FTL speeds. Do you feel any different? :)

Share this post


Link to post
Share on other sites
39 minutes ago, ronin said:

Presumably parts of it already are in relation to ourselves. Anything outside the Hubble Radius will be receeding from us at greater then C.

But get it understood that the objects are not themselves moving greater then C, but the gap between us and them is expanding at greater then C.

Look at it this way, place a box - nice stationary item - on one of the rubber walkway belts at Heathrow. How fast it is going?

It is stationary, the thing it is on is moving but it is not.

Spacetime is expanding and the distant galaxies are "on" that (as a stationary box is on the rubber belt), so they get carried away with it.

So the particles we not behave like they are moving faster than c - because they are stationary?

Also, why would anything outside the hubble radius "recced from us greater than c"?

1 hour ago, Peter Drew said:

No idea what the mass and time dilation issues would be but it would certainly limit the extent of the observable Universe.   :icon_biggrin:

I would really suck, the light will not be able to catch up with the expansion of the universe - so we wouldn't see it . :( 

Share this post


Link to post
Share on other sites

The name "Big bang" makes you think of a universe expanding or exploding into an universe, already being there. This is not the case, universe and the "emptyness" between galaxies was created (and still is) during Big Bang. There is no place from where this expansion started. It started from everywhere. Every place is the center of universe.

Share this post


Link to post
Share on other sites

The universe is already expanding at more than the speed of light if the distance over which the expansion is measured is large enough. That is what defines the 'observable universe' mentioned by Peter. Beyond that distance the expansion carries away light sources at more than c so we never receive their light. In a hyper-expanding universe the number of sources whose light will reach us gets ever smaller, as Peter said.

In the present situation gravitationally bound systems like galaxies are not expanding. However, perhaps if the value for the expansion became high enough galaxies themselves would be torn apart?

Remember that speed = distance/time. A distance has to be specified, so over what distance does the expansion of the universe exceed c?

Olly

  • Like 1

Share this post


Link to post
Share on other sites
On 3/28/2017 at 09:03, ollypenrice said:

The universe is already expanding at more than the speed of light if the distance over which the expansion is measured is large enough. That is what defines the 'observable universe' mentioned by Peter. Beyond that distance the expansion carries away light sources at more than c so we never receive their light. In a hyper-expanding universe the number of sources whose light will reach us gets ever smaller, as Peter said.

This is a very common misconception. The sphere which defines the point at which the recessional velocity is c is called the Hubble sphere but it is not the horizon of the observable universe. The CMB is the furthest we can see back. The sphere on which the CMB we observed today was emitted is receding from us at about 3.2c. At the time it was emitted it was receding at 58.1c! 

I have posted before a link to a paper that covers all this but I admit it is not easy going. So here is a "pop science"  explanation.  

Consider a star say 50 light years outside the Hubble sphere emitting a pulse of light towards us. We can certainly see stars 50 light years from us so there is no problem with the light moving towards the Hubble sphere in our direction. Eventually it will cross the Hubble sphere and continue on it's way towards us. It is now in a region moving away from us at less than the speed of light and so makes "real" progress towards us. 

Light can't reach the Hubble sphere on its way to us if it is emitted so far away from the Hubble sphere that it can't approach it i.e. it is receding from the Hubble sphere at c or greater. You might conclude that we could thus see back to a distance where the recessional velocity was 2c but we can in fact see further back as the Hubble sphere is in fact expanding away from us leading to the current 3.2c.

The exact figures are model dependent and the above is based on the currently accepted LCDM model.

Regards Andrew

The paper can be got from here https://arxiv.org/abs/astro-ph/0310808

 

Edited by andrew s
  • Like 1

Share this post


Link to post
Share on other sites
7 minutes ago, andrew s said:

This is a very common misconception. The sphere which defines the point at which the recessional velocity is c is called the Hubble sphere but it is not the horizon of the observable universe. The CMB is the furthest we can see back. The sphere on which the CMB we observed today was emitted is receding from us at about 3.2c. At the time it was emitted it was receding at 58.1c! 

I have posted before a link to a paper that covers all this but I admit it is not easy going. So here is a "pop science"  explanation.  

Consider a star say 50 light years outside the Hubble sphere emitting a pulse of light towards us. We can certainly see stars 50 light years from us so there is no problem with the light moving towards the Hubble sphere in our direction. Eventually it will cross the Hubble sphere and continue on it's way towards us. It is now in a region moving away from us at less than the speed of light and so makes "real" progress towards us. 

Light can't reach the Hubble sphere on its way to us if it is emitted so far away from the Hubble sphere that it can't approach it i.e. it is receding from the Hubble sphere at c or greater. You might conclude that we could thus see back to a distance where the recessional velocity was 2c but we can in fact see further back as the Hubble sphere is in fact expanding away from us leading to the current 3.2c.

The exact figures are model dependent and the above is based on the currently accepted LCDM model.

Regards Andrew

The paper can be got from here https://arxiv.org/abs/astro-ph/0310808

 

Indeed, I take your point. Thanks for a good explanation.

Olly

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.

  • Similar Content

    • By Kronos831
      Hi there! I’m looking forward towards purchasing a new wide FOV eyepiece from FLO (first light Optics ) and I do to know which one to pick!
      i will be using it on my f/6 8” Skywatcher dob and hoping to get good views of the Orion’s nebula , (large nebulae in general) andromeda and others.
      I ve heard the panaview 32mm is a good choice but I d like to know about the other options as well. I would like the budget to be around 100€
      Clear skies, Kronos.
    • By J47
      Hello stargazers, welcome. I had posted a picture yesterday of Uranus that had appeared to show its rings. I am using a Nexstar 4se, a 2x Barlow, and my Neximage Burst Color and capturing hundreds of photos and stacking them for my results. But still had me and others curious to if I were actually seeing the rings of Uranus or maybe just a glare of some sort.
      So I got back out there this morning, might I note I live in FL where the weather tends to stay hot so clear imaging during this time of year can be difficult, but not impossible as this image that I stacked 150 out of 300 images taken may show that statement holds true..............or I could just be mistaken the object in the image, but all in all I am feeling pretty confident that I have a decently clear image(stacked 150 images) of Uranus, its rings, and one of it's distant moons. It may be necessary to zoom in on my photo in order to see the moon it should be down and to the right of the planet a good distance in relation to the size of planet, I noticed that looking at Uranus in the photo helped bring the moon out just like stargazing in real-time. 
      If anyone can better distinguish what I might have done right or wrong here any help would be appreciated (also forgot to change format save for my images so I am stuck with .bmp and setting it as a download, sorry for any inconvenience.) - - - J47(JAY)
      uranusringmoon.bmp
    • By Kronos831
      Sooo after coming back from holidays(have been gone for a month and a half) i discovered that i had forgotten to use the lens caps to protect my Panaview 32mm from dust....
      turns out, its dirty.Me having no idea what a "multiple element lens eyepiece " meant , learnt the hard way. I unscrewed the bottom part of the eyepiece and 2 lenses and a tiny ring came out... not knowing in how to put them in, tried a bunch of different ways, and still the eyepiece view was still bad.(couldnt even focus on daylight objects) after messing with it for a bit 3-5 more lenses came out. Now my 100$ eyepiece is totally screwed up and i have No idea how to fix it. I m panicking so much and i have absolutely no idea what to do. I hope i ddnt screw the lens up...
        if anyone thinks they can help me, i m gonna make a system in which you can tell me how to put the lenses back
      So lets name the first group of parts depending on their place from left to right : A(The first lens ), B(the ring) and C( The Thrid lens) , now, these i have no idea how to place them correctly (have in mind that A Is curved , if it gives you any information)
      The next 4 pieces you see are D(The thick ring), E(The big lens) F (the other ring) and G(the final lens)
      Here is a picture of each piece from both up side and bottom side
      First will be up and second would be down
      If anyone could give me instructions to as how i can put everything back together , i would be greatful
      (Uploading pictures in a bit)
    • By Kronos831
      Hey guys! Its been 8 months since i ve started the hobby of astronomy.I would like to dig deeper now,i am looking for a book in astrophysics that involves mostly formulas and mathematics.With so many books in the market its hard to defferentiate science books from just books with information about the subject 
      Thanks!
      -Kronos
×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.