Physics Stack Exchange Question

I posted a [Physics Stack Exchange](http://physics.stackexchange.com/questions/171077) question about mass being lost in the universe and a possible consequence on the expansion of the universe. The original question was: How confident are we that mass is not being lost in the universe? After reading about the latest super-massive black hole in [Nature 518, 512–515 (26 February 2015)](http://www.nature.com/nature/journal/v518/n7540/full/nature14241.html), I couldn't help but wonder if the accelerating expansion is a result of mass being lost. My reasoning is as follows: 1. If the early universe had a particular (greater) mass than at present, 2. Then "space-time" could have had a "momentum" (determined by that mass) [1], 3. And that post-big-bang expansion was being retarded by existing mass [2], 4. But since then mass has been lost to the universe [3] 5. Which reduces the (retarding) due to gravity (less mass) [2] 6. Resulting in the "space-time" of the universe expanding faster [4] I was never a cosmologist, so please point out which of my assumptions are provably invalid! [1] Does spacetime have a "mass" value? or What is "Spacetime" made out of? [2] I'm struggling to remember my undergrad physics - would two particles each with an initial velocity moving away from each other in a gravitational field (relatively) speed up if the gravitational field is reduced? [3] Major assumption on my part! [4] Maybe! So I guess there are two questions here: A. How confident are we that mass is not being lost in the universe? and B. Would such a mass-loss be able to explain the observed accelerating expansion? --- It's been interesting to see how the question was edited down, and the resulting discussion!
@ 07:46 PM on March 19 | 0 Comments

Linux stuff: Adding WiFi access point to share 3G modem

The following changes were needed to share a 3G modem's internet connection via my laptop's WiFi acting as Access Point (AP). Assumptions: That all dependencies are installed and configured (hostapd, dnsmasq, 1. Disable NetworkManager from managing the WiFi Since laptop is running Ubuntu Trusty Tahr, I had to first disable network manager from managing the WiFi. Use the nm applet to disable WiFi. Note: editing the /etc/network/interfaces achieves this after next reboot. 2. Edit /etc/network/interfaces
iface wlan0 inet static
        address 192.168.0.1
        netmask 255.255.255.0
        broadcast 192.168.0.255
        post-up sleep 2 ; hostapd -B /etc/hostapd/minimal-wpa.conf ; service dnsmasq restart
        down pkill hostapd ; service dnsmasq restart
3. Configure hostapd /etc/hostapd/minimal-wpa.conf
#change wlan0 to your wireless device
interface=wlan0
driver=nl80211

# hostapd event logger configuration
#
# Two output method: syslog and stdout (only usable if not forking to
# background).
#
# Module bitfield (ORed bitfield of modules that will be logged; -1 = all
# modules):
# bit 0 (1) = IEEE 802.11
# bit 1 (2) = IEEE 802.1X
# bit 2 (4) = RADIUS
# bit 3 (8) = WPA
# bit 4 (16) = driver interface
# bit 5 (32) = IAPP
# bit 6 (64) = MLME
#
# Levels (minimum value for logged events):
#  0 = verbose debugging
#  1 = debugging
#  2 = informational messages
#  3 = notification
#  4 = warning
#
logger_syslog=-1
logger_syslog_level=3
logger_stdout=-1
logger_stdout_level=1

ctrl_interface=/var/run/hostapd
ctrl_interface_group=adm
country_code=ZA

ieee80211d=1
hw_mode=g

#ignore_broadcast_ssid=1
ignore_broadcast_ssid=0

ssid=ap_ssid
channel=6

#macaddr_acl=0
macaddr_acl=1
accept_mac_file=/etc/hostapd/hostapd.accept
deny_mac_file=/etc/hostapd/hostapd.deny


##### WPA/IEEE 802.11i configuration ##########################################

# Enable WPA. Setting this variable configures the AP to require WPA (either
# WPA-PSK or WPA-RADIUS/EAP based on other configuration). For WPA-PSK, either
# wpa_psk or wpa_passphrase must be set and wpa_key_mgmt must include WPA-PSK.
# For WPA-RADIUS/EAP, ieee8021x must be set (but without dynamic WEP keys),
# RADIUS authentication server must be configured, and WPA-EAP must be included
# in wpa_key_mgmt.
# This field is a bit field that can be used to enable WPA (IEEE 802.11i/D3.0)
# and/or WPA2 (full IEEE 802.11i/RSN):
# bit0 = WPA
# bit1 = IEEE 802.11i/RSN (WPA2) (dot11RSNAEnabled)
#wpa=1
wpa=3

# WPA pre-shared keys for WPA-PSK. This can be either entered as a 256-bit
# secret in hex format (64 hex digits), wpa_psk, or as an ASCII passphrase
# (8..63 characters) that will be converted to PSK. This conversion uses SSID
# so the PSK changes when ASCII passphrase is used and the SSID is changed.
# wpa_psk (dot11RSNAConfigPSKValue)
# wpa_passphrase (dot11RSNAConfigPSKPassPhrase)
#wpa_psk=0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef
wpa_passphrase=secret passphrase
4. dnsmasq configuration /etc/dnsmasq.conf
# global

# For debugging purposes, log each DNS query as it passes through
# dnsmasq.
log-queries

# wlan0
interface=wlan0
listen-address=192.168.0.1
dhcp-option=44,192.168.0.1     # set netbios-over-TCP/IP nameserver(s) aka WINS server(s)
dhcp-option=3,192.168.0.1

dhcp-range=net:wlan0,192.168.0.100,192.168.0.219,12h

dhcp-host=AA:BB:CC:DD:EE:FF,andy,192.168.0.212,600m
...etc...

5. Script to re-enable radio, start AP and enable NAT Assumes 3G modem is on wwan0.
#!/bin/bash
rfkill unblock `rfkill list | gawk '/phy0:/ {print substr($1,0,1)}'`
ifup wlan0
sleep 10
echo "1" > /proc/sys/net/ipv4/ip_forward
iptables --table nat --append POSTROUTING --out-interface wwan0 -j MASQUERADE
iptables --append FORWARD --in-interface wlan0 -j ACCEPT

@ 09:19 PM on August 10 | 0 Comments

Useful *nix command-line stuff

I'm capturing here a few hints and URLs to pages that contain useful *nix (Unix/Linux/etc) commands. Sometimes I forget a command that was once useful, so here I am capturing them for my long-term memory! [Linux Commands - A practical reference](http://www.pixelbeat.org/cmdline.html) # Simple Commands To do something with files in a directory, [easy syntax](http://www.cyberciti.biz/faq/bash-loop-over-file/): `` $ for f in *.c; do cmd $f; done `` I find this simpler than `find *.c -exec cmd {} \;`, which has the habit of including the file path (e.g. `./filename` in the command).
@ 02:59 PM on January 18 | 0 Comments

Toaster Pop-up fix

No, this is a real toaster (the thing that makes bread slices nice and crispy). I bought this cheap "SIMPEX" toaster from H&M in Ljubljana. Type 12415 1233 according to the label on the underside. Anyway, the thing stopped popping (actually, it stopped staying down.. I had to manually hold it down to toast my bread this morning). So I took it apart to see what was the matter.. Initially I found some dry joints. The electromagnet that magnetically keeps the toaster tray down was being stressed by the toaster tray, and two of the connecting pads lifted off the PCB. I fixed this by soldering some splices from the pins to other, more stable, locations on the PCB. But that didn't fix the problem... (well, it might have, originally, but my repair caused another issue..) It turns out that the "Cancel" button was always been pressed! The screws that hold the PCB with the cancel button on it seems to be able to tighten too much, causing the "cancel" button to be pressed in all the time, and hence prevent the latch mechanism from operating. The fix was a simple case of inserting an extra spacer under the PCB to stop the screws from pulling the PCB so far onto the plastic side thingy that it is mounted to. Having taken it apart, I can confirm that the latch mechanism is electromagnetic - there is an electromagnet that energizes and latches onto a plate attached to the toaster arm (this is a relief, I didn't want a purely mechanical system that could wear out).
@ 04:56 PM on August 31 | 0 Comments

Just upgrade admin

I was looking for a way to write to my Chyrp blog from my droid phone.. and it seems that all I needed to do was upgrade my Chyrp admin pages as decsribed in the [Chyrp Development blog](http://chyrp.net/discuss/development)
@ 03:30 PM on August 31 | 0 Comments

WHCMS does not support "org.za"

I had an issue with WHCMS (the web host management system) not correctly identifying that unused "org.za" domains where actually available. Whatever "org.za" domain I used, they would all fail with "Domain not available". The solution is to edit the .../includes/whoisservers.php file and change the "org.za" line to:
`.org.za|http://org.za/cgi-bin/rwhois?format=full&domain=|HTTPREQUEST-Domain not found`
@ 09:45 PM on July 02 | 0 Comments

Disabling adverts on the Samsung Galaxy Y Pro (B5510)

Have a look at [my latest post](http://www.kmz.co.za/blog/about-me/disabling-adverts-on-the-samsung-galaxy-y-pro-b5510/ "http://www.kmz.co.za/blog/about-me/disabling-adverts-on-the-samsung-galaxy-y-pro-b5510/") for some notes on how I edited my Samsung Galaxy Y Pro's "/etc/hosts" file, and blocked Google's adverts!
@ 05:11 PM on March 06 | 0 Comments

Postfix relaying using mail hosts based on "From" address

Have a look at my most recent page [setting up postfix to use different mail relays based on the email's "From" address](http://www.kmz.co.za/blog/getting-postfix-to-support-relaying-based-on-sender-address/ "http://www.kmz.co.za/blog/getting-postfix-to-support-relaying-based-on-sender-address/")
@ 09:29 PM on March 02 | 0 Comments

Integrating svn with Nautilus

Finally! A plugin that lets you access all your favourite subversion commands that integrates with Nautilus. And that works! I previously tried [RabbitCVS](http://rabbitvcs.org/ "RabbitCVS") but found that it totally sucked when I navigated into the Isis parent directory - it seemed to immediately recursively investigate all directories. Anyway, after a serendipitous [StackOverflow](http://stackoverflow.com/questions/86550/is-there-a-linux-ubuntu-svn-client-that-doesnt-suck "StackOverflow") search, I found [PagaVCS](http://code.google.com/p/pagavcs/ "PagaVCS"). [PagaVCS](http://code.google.com/p/pagavcs/ "PagaVCS") works really well, and it even has a [version](http://code.google.com/p/pagavcs/wiki/PagaVCS14Series "version") that installs on my Ubuntu 10.10 machine.
@ 06:16 PM on February 24 | 0 Comments

Apache Isis version 0.2.0-incubating Released

New Functionality ================== Have a look at the [Release Notes](http://incubator.apache.org/isis/release-notes-0.2.0-incubating.html "Release Notes") for the full list, but a selected highlight list: SQL/JDBC Database related ------------------ - Persist and restore polymorphic classes - Allow users to override "isis_" table prefix Other useful stuff ------------------ - JSON viewer (for Restful Objects, up to v0.56). - New "onlinedemo" example to demonstrate combined html and json viewers as live example. Other Improvements ================== After some internal discussion, we have revamped the Isis home page - hopefully it should now be more apparent what Isis is for, and how you can use it.
@ 01:10 PM on February 23 | 0 Comments

Tip: Hiding webapp port 8080 behind port 80

Use the Apache Webserver (httpd) to hide a webapp running on port 8080 behind port 80 (and even put it behind SSL).

I needed this when I found that a corporate firewall prevented access to my Isis webapp.

@ 06:19 PM on January 11 | 0 Comments

Apache Isis pages

Added Apache Isis Mini-pages, providing detailed content, in a hierarchical structure.

@ 02:51 PM on January 09 | 0 Comments

Apache Isis

I am a contributor to the Apache Isis project. In particular, I have been working on the Isis SQL ObjectStore, to allow domain information to be saved to any database with JDBC drivers. These pages will contain hints and techniques that I have picked up.
@ 03:37 PM on December 16 | 0 Comments