Craig Mayhew’s Blog

This follows on from my first article about harnessing time dilation. If you haven’t read my first article then I highly recommend you do before reading this one. I’ve included a spreadsheet so you can do these calculations yourself (available here). I’ve also improved the calculations accuracy and taken into account that there are not exactly 365 days in a year but instead 365.24219 days in a year. So this means the difference in seconds is slightly higher (more time!).

Time Dilation at the Earth’s equator:
Living on the equator means that due to the Earths spin you get an additional 465.1 m/s of velocity vs sitting on the pole (This does not take into account any wobble on the Earth’s axis). Compared to anyone sitting at the poles you would be 0.000038 seconds younger for each year that passes.

Over a 100 year life time: 3.8 milliseconds

Passenger Aircraft:
Flying in a plane can get you speeds of up to 917 m/s when in one of the latest Boeing 747s. Unfortunately that speed is not constant as it takes time to take off and get to the cruising speed. At 917 m/s if you cruise for 10 hours, you would be 0.168 microseconds younger than if you stayed on the ground. If you somehow managed to get a plane to fly non stop (refuel in the air?) then over a 1 year period you would be 0.0001476 seconds younger compared to if you were left on the ground.

Over a 100 year life time: 14.76 milliseconds

If we also take into account that you are flying east around the equator then we get 917 m/s from the plane and 465.1 m/s of velocity from the rotating Earth. At 1382.1 m/s you would gain 0.000335133072 seconds vs you sitting at one of the poles.

Over a 100 year life time: 33.54 milliseconds

Live on The International Space Station:
The ISS orbits the earth at 7706.6 m/s relative to the Earth’s center. If you had the money (or some serious negotiating skills) and managed to live on board the ISS each year you would be 0.0104198349888 seconds younger than if you had stayed on the north pole.

Over a 100 year life time: 1.043 seconds

Live on Mercury:
The planet Mercury orbits the sun at a fast paced 47.87 km/s. Although it would not be possible to live anywhere except on the poles due to high temperatures. Taking into account that the Earth is orbiting the Sun at 29.78km/s. At this speed (18.09 km/s) you would be 0.057 seconds younger per year than if you stayed back on Earth.

Over a 100 year life time: 5.75 seconds

If you were then able to get a satellite such as the ISS to be built around Mercury (obviously with some very effective heat/radiation shielding) You could gain an additional 6km/s in orbital speed giving you a difference of 24.09km/s compare to Earth.

Over a 100 year life time: 10.19 seconds

Hypothetical Limit to Orbital Velocity:
To hypothetically test the limitations of time dilation for an object in orbit around the sun we could create an artificial satellite with advanced heat shielding to allow us to get closer than mercury. We are limited by the fact that anything closer than 9 million km to the sun would not be in a stable orbit and would fall into the sun. We are also limited by the temperature being in excess of 1000 kelvin at 14 million km from the sun. So let’s go for 15 million km (0.1 AU) and hope our heat shielding holds out! At this distance we will get an orbital velocity of 91.96 km/s. With a difference of 62.18 km/s from Earth.

Over a 100 year life time: 67.88 seconds

Workings, Assumptions, Limitations:
Seconds in a year: 31556926 (taking into account leap years, seconds)
Speed of Light: 299792458 m/s
Velocity may be more complicated for objects orbiting planets. (Any input from someone in the field would be much appreciated)

When I have too many applications open or one of them eats all the memory I end up with a big chunk of my swap space used. The problem is that once I’ve closed a few programs or killed the offending program my computer still uses the swap space! I’ve read that the swap space will slowly be loaded back into RAM but only when it is next accessed. This results in sluggish system performance when the applications next read the memory in the swap space. To solve this problem you can empty the swap space and load it all back into RAM with one simple command. Please make sure you have enough RAM installed to load the memory in swap back into RAM…

This switches off swap memory and forces the system to load it back into RAM:

sudo swapoff -a

This switches swap back on incase you run out of RAM in the future:

sudo swapon -a

So now I can run those two commands, have the computer busy for 10-15 seconds and then know that it won’t slow down again due to needing to access the swap (Unless it runs out of RAM again).

Download VMWare Server from http://www.vmware.com/products/server/

Extract the tar file to somewhere convenient, in this case I’m going to extract it to the desktop.

Execute vmware-install.pl which is in the vmware-server-distrib folder that you just extracted. You will be prompted by questions about install directories. I managed to get away with pushing enter for the default value on all of these questions. It may need to recompile some files if it isn’t familiar with your kernel version. This isn’t normally a problem if you have a c/c++ compiler.

If you don’t have a c++ compile (here’s how to check and install one) then get one from synaptic packaged manager.

When asked, make sure you respond “yes” and give your ubuntu username when prompted to change the username (if this bit goes wrong then once VMWare Server is installed you will need to uninstall it and start over). After answering more prompts the installer will ask for your serial number. This can be obtained from the VMWare website for free.

Caveats:

1) If you accidentaly left the username blank then you will need to run the following command to uninstall the vmware server. You will then need to start the install again.

sudo /usr/bin/vmware-uninstall.pl

2) To access the server admin you need to visit either https://127.0.0.1:8333/ui/ or http://127.0.0.1:8222/ui/ in a browser. You can then login with your ubuntu account username and password.

Click the System Menu and then click “Synaptic Package Manger”:

Then type gcc into the quick search box. The list may make take a moment to update. Then if you don;t have a blue box next to gcc like I have in the example then click the empty box and click “Apply” to install the gcc package.

The new network manager is a massive improvement over the previous network tools in Ubuntu. Coming from a windows background I am used to routing tables being updated automatically. However, after connecting to a VPN using the Ubuntu 9.04 network manager I’m unable to access or even ping anything on the remote network, yet the VPN is connected. This is due to the computer not knowing about the computers on the VPN. This is where routing tables come into play. My works ip range is 192.168.10.* so this needs to be added to the routing table.

The easiest way to do this is to have the network manager handle it all by adding a setting in the network manager like so:

Click on the network manager icon then “VPN Connections” and the following menu should appear: Click “Configure VPN”.

Click the VPN tab. The VPN you have already created should appear in the list. Click your VPN and then click edit.

Another window should appear, click the “IPv4 Settings” tab. Then click the “Routes…” button.

Now you need to add a route so your computer can talk to other computers on the VPN. In this case I have added the address as 192.168.10.0 as all computers on the office network have an IP that begins with “192.168.10″ and a netmask of 255.255.255.0. The gateway is the IP of my home router, in this case my home router is “10.11.12.1″.

At this point it’s also worth mentioning as a side note that if “Use this connection only for resources on its network” is NOT ticked then all of your regular internet traffic will go via the VPN and not just when you want to access something on VPN like shared files and folders. This would really slow down your internet access. I personally would have this ticked.

And there you have it, that will now allow your computer to talk to other computers on the office/remote network.

For those of you who want a more hands on approach and really want to see whats going on behind the scenes (everyone else stop reading here):

Run the route command to view the routing table:

route

This is the route table with the missing route:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
office.mywork   my.router       255.255.255.255 UGH   0      0        0 eth2
10.11.0.0       *               255.255.0.0     U     1      0        0 eth2
link-local      *               255.255.0.0     U     1000   0        0 eth2
default         my.router       0.0.0.0         UG    0      0        0 eth2

The network manager automatically adds the correct route to the routing table when the VPN connection is created. You can achieve the same result with the following command. In this case we are using the network range 192.168.10.*:

sudo route add -net 192.168.10.0/24 ppp0

Now check the routes table again:

route

And here we have a route that allows us to access computers on the remote network:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
office.mywork   10.11.12.1      255.255.255.255 UGH   0      0        0 eth2
192.168.10.0    *               255.255.255.0   U     0      0        0 ppp0
10.11.0.0       *               255.255.0.0     U     1      0        0 eth2
link-local      *               255.255.0.0     U     1000   0        0 eth2
default         10.11.12.1      0.0.0.0         UG    0      0        0 eth2

Beth found this in the change of the BBQ takings at the Cowfold fair.

It’s one of the 2009 mismatched coins that has no date and we are auctioning it for charity.

The ebay auction can be found here http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=130316755681